Recent zbMATH articles in MSC 83https://zbmath.org/atom/cc/832024-02-28T19:32:02.718555ZWerkzeugFrom John Mitchell to Sagittarius A\(^*\): an equation holdshttps://zbmath.org/1527.010392024-02-28T19:32:02.718555Z"Funke, Klaus"https://zbmath.org/authors/?q=ai:funke.klausSummary: On the 12th of May 2022 a picture went around the globe. It was the image of the bright surroundings of the black hole which is situated at the galactic centre of the Milky Way, called Sagittarius A\(^*\) (Sgr A\(^*\)). The mass of Sgr A\(^*\) is about four million times that of the sun. Remarkably, this image is in perfect agreement with Einstein's theory of general relativity. In fact, the detected size of the event horizon is exactly the one predicted by that theory, thus confirming the validity of an equation published in 1916 by Karl Schwarzschild. Interestingly, the same equation had already been derived in the late eighteenth century, on the basis of Newtonian physics.Partial differential equations. III: Nonlinear equationshttps://zbmath.org/1527.350042024-02-28T19:32:02.718555Z"Taylor, Michael E."https://zbmath.org/authors/?q=ai:taylor.michael-eugenePublisher's description: The third of three volumes on partial differential equations, this is devoted to nonlinear PDE. It treats a number of equations of classical continuum mechanics, including relativistic versions, as well as various equations arising in differential geometry, such as in the study of minimal surfaces, isometric imbedding, conformal deformation, harmonic maps, and prescribed Gauss curvature. In addition, some nonlinear diffusion problems are studied. It also introduces such analytical tools as the theory of \(L^p\) Sobolev spaces, Holder spaces, Hardy spaces, and Morrey spaces, and also a development of Calderon-Zygmund theory and paradifferential operator calculus. The book is targeted at graduate students in mathematics and at professional mathematicians with an interest in partial differential equations, mathematical physics, differential geometry, harmonic analysis, and complex analysis.
The third edition further expands the material by incorporating new theorems and applications throughout the book, and by deepening connections and relating concepts across chapters. It includes new sections on rigid body motion, on probabilistic results related to random walks, on aspects of operator theory related to quantum mechanics, on overdetermined systems, and on the Euler equation for incompressible fluids. The appendices have also been updated with additional results, ranging from weak convergence of measures to the curvature of Kahler manifolds.
Michael E. Taylor is a Professor of Mathematics at the University of North Carolina, Chapel Hill, NC.
Review of first edition: ``These volumes will be read by several generations of readers eager to learn the modern theory of partial differential equations of mathematical physics and the analysis in which this theory is rooted.''
(Peter Lax, SIAM review, June 1998)
See the reviews of Vol. I--III of the first edition in [Zbl 0869.35002; Zbl 0869.35003; Zbl 0869.35004]. See the reviews of Vol. I--III of the second edition in [Zbl 1206.35002; Zbl 1206.35003; Zbl 1206.35004]. For Vol. I and II of the third edition see [Zbl 1527.35002; Zbl 1527.35003].Complex coupled dispersionless equations in Minkowski 3-spacehttps://zbmath.org/1527.353492024-02-28T19:32:02.718555Z"Eren, Kemal"https://zbmath.org/authors/?q=ai:eren.kemal"Ersoy, Soley"https://zbmath.org/authors/?q=ai:ersoy.soleySummary: In this study, we investigate the geometric and algebraic aspects of defocusing Complex Coupled Dispersionless (CCD) equations in Minkowski space. We give the conditions for obtaining CCD equations from moving spacelike or timelike space curves using the Frenet and Darboux frames. Besides, we present the Lax pairs that indicate that the corresponding CCD equations are integrable. Finally, we evaluate the conserved quantities for CCD equations from the geometric point of view.Betchov-Da Rios equation by null Cartan, pseudo null and partially null curve in Minkowski spacetimehttps://zbmath.org/1527.353762024-02-28T19:32:02.718555Z"Erdoğdu, Melek"https://zbmath.org/authors/?q=ai:erdogdu.melek"Li, Yanlin"https://zbmath.org/authors/?q=ai:li.yanlin"Yavuz, Ayşe"https://zbmath.org/authors/?q=ai:yavuz.ayseSummary: The aim of this paper is to investigate Betchov-Da Rios equation by using null Cartan, pseudo null and partially null curve in Minkowski spacetime. Time derivative formulas of frame of \(s\) parameter null Cartan, pseudo null and partially null curve are examined, respectively. By using the obtained derivative formulas, new results are given about the solution of Betchov-Da Rios equation. The differential geometric properties of these solutions are obtained with respect to Lorentzian causal character of \(s\) parameter curve. For a solution of Betchov-Da Rios equation, it is seen that null Cartan \(s\) parameter curves are space curves in three-dimensional Minkowski space. Then all points of the soliton surface are flat points of the surface for null Cartan and partially null curve. Thus, it is seen from the results obtained that there is no surface corresponding to the solution of Betchov-Da Rios equation by using the pseudo null \(s\) parameter curve.On the stability of relativistic perfect fluids with linear equations of state \(p=K\rho\) where \(1/3<K<1\)https://zbmath.org/1527.354162024-02-28T19:32:02.718555Z"Marshall, Elliot"https://zbmath.org/authors/?q=ai:marshall.elliot"Oliynyk, Todd A."https://zbmath.org/authors/?q=ai:oliynyk.todd-andrewSummary: For \(1/3<K<1\), we consider the stability of two distinct families of spatially homogeneous solutions to the relativistic Euler equations with a linear equation of state \(p=K\rho\) on exponentially expanding FLRW spacetimes. The two families are distinguished by one being spatially isotropic while the other is not. We establish the future stability of nonlinear perturbations of the non-isotropic family for the full range of parameter values \(1/3<K<1\), which improves a previous stability result established by the second author that required \(K\) to lie in the restricted range (1/3, 1/2). As a first step towards understanding the behaviour of nonlinear perturbations of the isotropic family, we construct numerical solutions to the relativistic Euler equations under a \(\mathbb{T}^2\)-symmetry assumption. These solutions are generated from initial data at a fixed time that is chosen to be suitably close to the initial data of an isotropic solution. Our numerical results reveal that, for the full parameter range \(1/3<K<1\), the density gradient \(\frac{\partial_x \rho}{\rho}\) associated to a nonlinear perturbation of an isotropic solution develops steep gradients near a finite number of spatial points where it becomes unbounded at future timelike infinity. This behavior of the density gradient was anticipated by \textit{A. D. Rendall} [Ann. Henri Poincaré 5, No. 6, 1041--1064 (2004; Zbl 1061.83008)], and our numerical results confirm his expectations.Local wellposedness of the relativistic Vlasov-Poisson equation in Besov spacehttps://zbmath.org/1527.354242024-02-28T19:32:02.718555Z"Wang, Yiliu"https://zbmath.org/authors/?q=ai:wang.yiliu"Zhang, Xianwen"https://zbmath.org/authors/?q=ai:zhang.xianwenSummary: We obtain the local existence and uniqueness of solution to the relativistic Vlasov-Poisson system in Besov space, extending the non-relativistic result to the relativistic case. Weaker regularity is required for the initial datum by optimizing the commutator estimates related to the field. Commutator estimates associated with relativistic velocity are proved by dyadic decomposition of the frequency space and the decreasing properties of Bessel potential.A fixed point approach for tuning circuit problem in dislocated \(b\)-metric spaceshttps://zbmath.org/1527.470172024-02-28T19:32:02.718555Z"Younis, Mudasir"https://zbmath.org/authors/?q=ai:younis.mudasir"Singh, Deepak"https://zbmath.org/authors/?q=ai:singh.deepak-kumar"Abdou, Afrah A. N."https://zbmath.org/authors/?q=ai:abdou.afrah-ahmad-noan(no abstract)Geometric aspects of quasi-local mass and Gromov's fill-in problemhttps://zbmath.org/1527.530292024-02-28T19:32:02.718555Z"Hu, Xue"https://zbmath.org/authors/?q=ai:hu.xue"Shi, Yuguang"https://zbmath.org/authors/?q=ai:shi.yuguangIn this chapter, the authors discuss the connection between the boundary geometry and the interior geometry of compact Riemann manifolds, with an emphasis on different aspects of the positive mass definition and its properties.
The first section of this chapter is devoted to a brief review of the problem of the extension of a Riemannian metric on the boundary of a compact manifold to a Riemannian metric of positive scalar curvature on the interior. This problem, formulated for the first time by Gromov, was answered positively by \textit{Y. Shi} et al. [J. Reine Angew. Math. 784, 215--250 (2022; Zbl 07502527)]. However, the non-negativity of the mean curvature for the boundary was left unanswered. The rest of the first section reviews the concepts and the main results from the formulation of the extension problem as a non-negative scalar curvature (NNSC) fill-in problem in terms of Bartnik data and the review of the ADM mass. The authors recall that they will restrict the discussion to the existence of NNSC fill-in, and list important properties that quasi-local mass of Bartnik data, an important concept in both mathematics and physics, will have when NNSC fill-ins exist. Section 1 ends with the review of the quantity \(\Lambda_{+} ( \Sigma^{n-1}, \gamma)\) introduced by \textit{C. Mantoulidis} and \textit{P. Miao} [Commun. Math. Phys. 352, No. 2, 703--718 (2017; Zbl 1375.58017)] and associated with a function \(H\) of the Bartnik data, which is actually interpreted as being the mean curvature. The quantity \(\Lambda_{+} ( \Sigma^{n-1}, \gamma)\) can be used as a criterion for the positive mass theorem. The known facts around this quantity and positive mass are listed for asymptotically hyperbolic and asymptotically flat manifolds.
Section 2 discusses the quasi-local mass and NNSC fill-in for Bartnik data. Hawking mass, Bartnik mass, Brown-York mass and the connection to NNSC fill-ins are reviewed in detail.
Section 3 focusses on NNSC-cobordism and its connection to the quasi-masses. It is recalled that the Hawking mass and the Brown-York mass can be used to establish a criterion for the non-existence of trivial NNSC-cobordisms. NNSC-cobordisms are important in this context because they connected to the fill-in problem.
The chapter represents a very interesting review of the topics mentioned in its title. The essential theorems to follow the connections among the concepts are clearly stated and commented. The references where proofs can be found are given. The results presented here are useful to both researchers in the field of mathematical relativity and to graduate students in this field.
For the entire collection see [Zbl 1517.53004].
Reviewer: Ion Vancea Vancea (Rio de Janeiro)Initial value problem for the constant mean curvature equation in the Reissner-Nordström spacetimehttps://zbmath.org/1527.530572024-02-28T19:32:02.718555Z"Lee, Kuo-Wei"https://zbmath.org/authors/?q=ai:lee.kuo-weiSummary: We characterize all spacelike and spherically symmetric constant mean curvature hypersurfaces in the maximally extended Reissner-Nordström spacetimes. These characterizations also provide a proof of the existence and uniqueness of the initial value problem for the spacelike and spherically symmetric constant mean curvature equation in the maximally extended Reissner-Nordström spacetimes.Hawking-Penrose black hole model. Large emission regimehttps://zbmath.org/1527.600582024-02-28T19:32:02.718555Z"Pechersky, E."https://zbmath.org/authors/?q=ai:pechersky.eugeny|pechersky.eugene-a"Pirogov, S."https://zbmath.org/authors/?q=ai:pirogov.sergei-a"Yambartsev, A."https://zbmath.org/authors/?q=ai:yambartsev.anatoly-aSummary: In this paper, we propose a stochastic version of the Hawking-Penrose black hole model. We describe the dynamics of the stochastic model as a continuous-time Markov jump process of quanta out and in the black hole. The average of the random process satisfies the deterministic picture accepted in the physical literature. Assuming that the number of quanta is finite the proposed Markov process consists of two components: the number of the quanta in the black hole and the amount of the quanta outside.
The stochastic representation allows us to apply large deviation theory to study the asymptotics of probabilities of rare events when the number of quanta grows to infinity. The theory provides explicitly the rate functional for the process. Its infimum over the set of all trajectories leading to large emission event is attained on the most probable trajectory. This trajectory is a solution of a highly nonlinear Hamiltonian system of equations. Under the condition of stationarity of the fraction of quanta in the black hole, we found the most probable trajectory corresponding to a large emission event.Problems of experimental verification of the theory of general relativityhttps://zbmath.org/1527.700202024-02-28T19:32:02.718555Z"Zhuravlev, V. F."https://zbmath.org/authors/?q=ai:zhuravlev.viktor-filippovich(no abstract)Electrodynamicshttps://zbmath.org/1527.780012024-02-28T19:32:02.718555Z"Petrascheck, Dietmar"https://zbmath.org/authors/?q=ai:petrascheck.dietmar"Schwabl, Franz"https://zbmath.org/authors/?q=ai:schwabl.franzDas gut geschriebene Buch von F. Schwabl und D. Petrascheck kann als Ergänzung der Lehrbuchreihe von \textit{F. Schwabl}
\begin{itemize}
\item Quantenmechanik. Eine Einführung [Zbl 1166.81003; Englisch: Zbl 1166.81002]
\item Quantenmechanik für Fortgeschrittene [Zbl 1088.81005; Englisch: Zbl 1039.81001]
\item Statistische Mechanik [Zbl 1113.82001; Englisch: Zbl 1131.82001]
\end{itemize}
gesehen werden. Das XVII + 615 Seiten umfassende und nach praktischen Gesichtspunkten gegliederte Lehrbuch besteht aus einem Vorwort, einem ausführlichen Inhaltsverzeichnis, einer Einleitung, 13 Kapiteln, 3 Anhängen und einem siebenseitigen Sachwortverzeichnis. In den Anhängen sind die für das Verständnis der physikalischen Themen nötigen mathematischen Hilfsmittel in einem Umfang zusammengestellt, wie sie im Allgemeinen in Vorlesungen für Studierende der Physik geboten werden. Vor allem aus Gründen der Konsistenz zu den oben genannten Lehrbüchern von F. Schwabl wird das Gaußsche System als Maßsystem verwendet. Eine Übersetzungstabelle vom Gaußschen zum SI-System befindet sich im Anhang. Am Ende eines jeden Kapitels werden dem Leser Übungsaufgaben angeboten. Zugehörige Musterlösungen können von einer Internetseite heruntergeladen werden.
In der Einleitung skizzieren die Autoren die historische Entwicklung der Elektrodynamik, beginnend mit dem Hinweis, dass bereits in der Antike einfache elektromagnetische Erscheinungen beobachtet wurden. Eine genaue Beschreibung der entscheidenden wissenschaftlichen Etappen startet mit der Erkenntnis des Erdmagnetismus durch W. Gilbert (1544--1603). Im Folgenden werden in gleicher Weise in Verbindung mit den Namen der Entdecker (C. A. de Coulomb, A. Volt, H. C. Ødter, A. M. Ampère, M. Faraday, J. C. Maxwell, H. Hertz, H. A. Lorenz und A. Einstein, um nur einige zu nennen) die wesentlichen Fortschritte skizziert.
Das Buch umfasst im Wesentlichen die klassische Elektrodynamik einschließlich der Speziellen Relativitätstheorie, unterscheidet sich aber gegenüber vergleichbaren Monografien durch eine ausführliche Behandlung bestimmter Themen. Dazu gehören die Potentialtheorie in der Elektrostatik, Gebiete der Festkörperphysik mit einem Bezug zur Elektrodynamik (z. B. Clausius-Mossotti-Formel und Hall-Effekt) und die dynamische Theorie der Röntgen- und Neutronenstrahlung. Ausführlich wird insbesondere die Spezielle Relativitätstheorie behandelt. Dagegen wird auf die geometrische Optik und technische Anwendungen in Netzwerken weniger eingegangen. Die nichtlineare Optik, Quantenoptik und die Quantenelektrodynamik sind nicht Gegenstand des Werkes. Für die für viele Spezialgebiete formulierten Maxwellschen Gleichungen werden analytische Lösungen hergeleitet, die numerische Behandlung der Gleichungen gehört nicht zu den Aufgaben der Publikation.
In dem ersten Kapitel werden die Maxwellschen Gleichungen eingeführt, beginnend mit der Aussage, dass in der Elektrodynamik ``die durch ruhende und bewegte Ladungen erzeugten elektrischen und magnetischen Felder und Bewegungen'' sowie ``die Wechselwirkung von geladenen Teilchen unter dem Einfluss elektromagnetischer Felder behandelt werden''.
Die Grundbegriffe Elektronen, Protonen, Ladungsträger, Elementarladung, Ordnungszahl der Ladung, Größe einer Ladung, CGS- und SI-Einheitensystem sowie die Ladungsdichte werden ausführlich dargestellt. Das Faradaysche Gesetz, die experimentelle Bestimmung des Wertes der Elementarladung durch Millikan, der Erhaltungssatz für Ladungen und die Behandlung der Ladungsträger als Punktteilchen (Vernachlässigung der Ausdehnung der Teilchen) werden beschrieben. Ausgehend von der Gesamtladung eines Atomkerns werden die Raumladungsdichte, die mikroskopische Ladungsdichte \( \rho(x,t) \) und die mikroskopische Stromdichte \( \vec{j}(x,t) \) eingeführt. Letztere erfüllen die Kontinuitätsgleichung. Die Stromdichte wird auch mit Hilfe einer mittleren Geschwindigkeit der Ladungsträger dargestellt. Im Folgenden wird nach Mittelungen der Begriffe der Übergang zu kontinuierlichen Ladungsverteilungen erklärt mit dem Ergebnis, dass im Allgemeinen nicht mehr zwischen mikroskopischen, mittleren und kontinuierlichen Dichten und Strömen unterschieden werden muss und nur noch \( \rho \) und \( \vec{j} \) verwendet werden. Unter Verwendung des Gaußschen Satzes erhält man neben der differentiellen Darstellung auch die integrale Form der Kontinuitätsgleichung.
Im zweiten Abschnitt des Kapitels wird das Coulombsche Gesetz für die Kraft, die zwei ruhende Ladungen aufeinander ausüben, beschrieben und hervorgehoben, dass für bewegte Ladungen neben der Coulomb-Kraft noch die Lorentz-Kraft zu berücksichtigen ist, die die Ablenkung bewegter Teilchen in einem Magnetfeld wiedergibt. Bewegte Ladungen erzeugen ein elektrisches Feld \( \vec{E} \) und ein magnetisches Feld \( \vec{B}\), ruhende Ladungen dagegen nur ein elektrostatisches Feld \( \vec{E} \). Zur Beschreibung der elektromagnetischen Vorgänge durch die Maxwellschen Gleichungen in Materie werden sogenannte Hilfsfelder eingeführt, die dielektrische Verschiebung \( \vec{D} \) und das Magnetfeld \( \vec{H} \). In den Maxwellschen Gleichungen wird das Magnetfeld \( \vec{B} \) (bekannt als magnetische Flussdichte oder magnetische Induktion) verwendet, dessen Wirkung auf bewegte Ladungen experimentell messbar ist. Die physikalische Bedeutung der Hilfsfelder \( \vec{D} \) und \( \vec{H} \) besteht darin, dass die von den gebundenen Ladungen herrührende Polarisation zu dem Feld \( \vec{E} \) und die von den gebundenen Strömen verursachte Magnetisierung zu dem Feld \( \vec{B} \) addiert wird.
Die Maxwellschen Gleichungen beschreiben das Verhalten geladener Teilchen in elektromagnetischen Feldern. Sie werden im dritten Abschnitt des Kapitels in differentieller und integraler Form ausführlich behandelt. Die Autoren weisen darauf hin, dass die Gleichungen auf Erfahrungen mit elektrodynamischen Phänomenen beruhen und daher in der Elektrodynamik eine ähnliche Bedeutung haben wie die Newtonschen Axiome in der Mechanik.
Nach der Definition der Begriffe ``Elektrischer und Magnetischer Fluss durch eine Fläche'' und ``Magnetische und Elektrische Ringspannung (Zirkulation)'' werden die vier Gesetze der Maxwellschen Gleichungen hergeleitet, das Gaußsche Gesetz, das Faradaysche Induktionsgesetz, das Ampére-Maxwellsche-Gesetz und die Divergenzfreiheit des Magnetfeldes \( \vec{B} \) (für dieses Buch in dieser Reihenfolge).
Des Weiteren wird das Superpositionsprinzip behandelt. Es werden weitere Gründe, neben den in der Einleitung genannten, für die Beibehaltung des Gaußschen Maßsystems in der Elektrodynamik und der speziellen Relativitätstheorie erläutert.
Am Ende des Kapitels werden die Maxwellschen Gleichungen zusammen mit der Kontinuitätsgleichung und der Lorentz-Kraft benutzt, um Gebiete der Elektrodynamik, die in den folgenden Kapiteln behandelt werden, in einem Flussdiagramm darzustellen.
Dazu gehört die Aufspaltung von gebundenen Ladungen und Strömen, die zu einer Aufteilung der Felder und einer Umstrukturierung der Maxwellschen Gleichungen führt. Als Beispiel wird ein einem starken elektrischen Feld ausgesetztes Atom genannt, bei dem sich die Elektronenhülle gegenüber dem Kern nur verschiebt und die Bindung zum Kern erhalten bleibt. Diese Elektronen sind anders zu behandeln als freie Elektronen.
Auch die Beachtung der Zeitskala, auf der sich die elektromagnetischen Vorgänge abspielen, führt zu Differenzierungen.
In zeitunabhängigen Fällen findet eine Entkopplung in elektrische und magnetische Anteile statt.
In zeitlich langsamen Veränderungen wird der Verschiebungsstrom vernachlässigt, der Strom ist dann quellenfrei, und es gibt keine radiative Strahlung. Als Beispiele für diesen Effekt werden elektrische Netzwerke, die London-Gleichungen (Supraleitung, Meissner-Effekt), der Skin-Effekt und die Magnetohydrodynamik genannt.
Zu den schnell veränderlichen Vorgängen zählen die elektromagnetischen Felder, Teile der Optik und die dynamische Theorie der Röntgen-Beugung.
Nicht zu den obigen Einteilungen, aber in diesem Buch behandelt, gehört die Bewegung des Elektrons in einem äußeren Feld. Hier werden die Euler-Lagrange-Gleichungen der klassischen Mechanik zusammen mit der Lorentz-Kraft behandelt.
Auch die zu behandelnde Spezielle Relativitätstheorie liegt außerhalb des obigen Rahmens. Hier sind ``die Maxwellschen Gleichungen kovariant unter der Lorentz-Transformation, nicht aber die Gesetze der klassischen Mechanik, so dass letztere umgeformt werden müssen''.
Erwähnt sei noch, dass die Autoren neben den durchgängig verwendeten Bezeichnungen der Begriffe auch auf alternativ übliche oder veraltete Termini hinweisen.
In den folgenden Kapiteln werden die in Kapitel 1 eingeführten allgemeinen Maxwellschen Gleichungen entsprechend dem oben genannten Flußdiagramm auf die verschiedenen Gebiete heruntergebrochen und teilweise mit anderen Gleichungen kombiniert. Für eine Vielzahl spezieller Aufgabenstellungen werden analytische Lösungen hergeleitet. Berechnungen werden teilweise mit großer Ausführlichkeit wiedergegeben, mit Hinweisen derart, dass der nur an einem eher grundsätzlichen Verständnis interessierte Leser diese übergehen kann. Die Wiedergabe des Umfangs der vielen Teilprobleme übersteigt den Sinn eines Reviews. Es werden daher im Folgenden nur die wesentlichen Belange der einzelnen Kapitel beschrieben.
In Kapitel 2 werden ruhende elektrische Ladungen und die Verteilung der Elektrizität auf Leitern behandelt. Im ersten Abschnitt geht es um die Elektrostatik, in der die Ladungsdichte \( \rho \) zeitunabhängig ist und die Stromdichte \( \vec{j} \) verschwindet. \( \vec{E} \) und \( \vec{B} \) sind dann auch zeitunabhängig. Ihre zeitliche Ableitung verschwindet daher, was zu einer Entkopplung der Maxwellschen Gleichungen mit den zwei Gebieten Elektrostatik und Magnetostatik führt. Für die Elektrostatik folgt dann aus dem Faradayschen Induktionsgesetz die Wirbelfreiheit des elektrischen Felds, das dadurch wiederum als Gradient eines skalaren Potentials \( \Phi \) dargestellt werden kann. Durch das Einsetzen des Gradienten in das Gaußsche Gesetz ergibt sich die Poissongleichung, für die mittels der Greenschen Funktion eine analytische Lösung ermittelt wird. Weitere Themen des Kapitels sind die Potentialdifferenz (Spannung), Ladungsverteilungen (Punktladung, elektrischer Dipol, Quadrupol, Linien- und Flächenladung), Feldlinien, Stetigkeitsbedingungen, Kondensatoren, Faraday-Käfig, Felder in besonderen Fällen, Wechselwirkungsenergien, Kräfte und Momente, die Ladungsverteilungen aufeinander ausüben, Satz von Thompson und die Multipolentwicklung.
Im dritten Kapitel werden Dirichletsche und Neumannsche Randwertprobleme der Elektrostatik in Kugel- und Zylinderkoordinaten untersucht. Die Eindeutigkeit der Lösung der Poissongleichung mit Randbedingung wird hergeleitet. Die Lösungen der Poisson- und Laplace-Gleichungen mit Hilfe Greenscher Funktionen mit den beiden Randbedingungen werden unter Einbeziehung gewählter Oberflächen entwickelt. Basierend auf diesen Ergebnissen werden auf 40 Seiten detaillierte Spezialfälle behandelt, auf die hier nicht weiter eingegangen wird.
Im letzten Abschnitt wird noch eine mit der Anwendung der konformen Abbildung in der Potentialtheorie verbundene funktionentheoretische Methode für spezielle zweidimensionale Probleme vorgestellt.
In Kapitel 4 werden folgerichtig die Grundgleichungen der Magnetostatik erörtert, die sich nur auf das Magnetfeld \( \vec{B} \) und die zeitunabhängige Stromdichte \( \vec{j} \) beziehen. Die Maxwellschen Gleichungen umfassen hier also nur die Ampére-Maxwell-Gleichung (ohne Verschiebungsstrom) und die Divergenzfreiheit von \( \vec{B} \). Aus letzterer folgt, dass \( \vec{B} \) durch das Vektorpotential \( \vec{A} \) dargestellt werden kann. Aus den beiden Gleichungen wird die Vektor-Poisson-Gleichung für \( \vec{A} \) hergeleitet, die komponentenweise analog zur Elektrostatik für das skalare Potential behandelt werden kann. Das Magnetfeld \( \vec{B} \) wird aus dem Vektorpotential \( \vec{A} \) berechnet (Biot-Savart-Gesetz).
Analog zur Elektrostatik werden anschließend, basierend auf diesen Ergebnissen, eine Vielzahl spezieller Probleme analysiert.
Der Titel des 5. Kapitels lautet ``Elektromagnetische Vorgänge in Materie''. In den beiden vorangegangenen Kapiteln wurden zeitunabhängige Prozesse betrachtet, die Materie spielte keine Rolle. Der Übergang zu den makroskopischen Gleichungen (Maxwellgleichungen in Materie) erfolgt durch Einführung mittlerer Felder, einer mittleren Ladungsverteilung und einer mittleren Stromverteilung. In Materie sind Atome und Moleküle nicht frei beweglich, sondern an ihre Gitterplätze gebunden. Sie haben die Eigenschaft neutral zu sein, Ionen zu sein oder permanente Dipol- oder auch Multipolmomente zu haben. Unter der Einwirkung elektromagnetischer Felder verschieben sich die Ladungen von Kern und Elektronenhülle gegeneinander, ohne die Bindung zu verlieren (gebundene Ladungen). Es entsteht ein induziertes Dipolmoment. Höhere Multipolmomente werden auf Grund ihrer relativen Kleinheit vernachlässigt. Es sind also freie und gebundene Ladungen und Ströme zu unterscheiden. In Materie wird nun die von den gebundenen Ladungen herrührende Polarisation \( \vec{P} \) zu dem Feld \( \vec{E} \) und die auf den gebundenen Strömen basierende Magnetisierung \( \vec{M} \) dem Feld \( \vec{H} \) hinzugefügt (Materialgleichungen), so dass sich nach einigen Umformungen schließlich die Maxwell-Gleichungen in Materie ergeben.
Ein geschlossenes System bilden die Maxwell-Gleichungen erst zusammen mit den Materialgleichungen (auch konstitutive Gleichungen genannt). Die Polarisation ist dabei proportional zu \( \vec{E} \) mit der sogenannten elektrischen Suszeptibilität als Proportionalitätsfaktor. Das Verschiebungsfeld \( \vec{D} \) wird entsprechend durch die Dielektrizitätskonstante (oder elektrische Feldkonstante) und die Magnetisierung \( \vec{M} \) durch die magnetische Permeabilität (oder magnetische Feldkonstante) definiert. Ein lineares Medium liegt vor, wenn die beiden Konstanten keine Funktionen von \( \vec{E} \) oder \( \vec{H} \) sind.
Von den Themen, die neben den Maxwell-Gleichungen in Materie in diesem Kapitel erörtert werden, seien hier einige aufgezählt:
Drude-Modell, Joulesche Wärme, Hall-Effekt, Hamiltonsches Prinzip, London-Gleichungen, Meissner-Ochsenfeld-Effekt, atomare, elektronische und ionische Polarisierbarkeit, Drude-Lorentz-Modell, Kramers-Kronig-Dispersionsrelationen, Energie- und Impulsbilanz.
In Kapitel 6 werden die Grundgleichungen für die Elektrostatik in Materie formuliert. Die Maxwellschen Gleichungen entkoppeln sich, da aufgrund der Zeitunabhängigkeit die zeitlichen Ableitungen von \( \vec{D} \) und \( \vec{B} \) verschwinden. Die Entkopplung wirkt sich auf die Stetigkeitsbedingungen aus. Im Unterschied zum Vakuum, in dem nur Stetigkeitsbedingungen an Grenzflächen zu Leitern und Flächenladungen betrachtet wurden, sind jetzt auch Grenzflächen zu Dielektrika zu beurteilen. Die Stetigkeitsbedingungen werden für zahlreiche Anwendungen diskutiert, zum Beispiel für das Dielektrikum im Plattenkondensator oder für die dielektrische Kugel in einem äußeren Feld. Im Abschnitt ``Clausius-Mossotti-Formel'' wird die makroskopisch messbare Dielektrizitätskonstante mit der atomaren Polarisierbarkeit in einem Kristall mit kubischer Symmetrie verknüpft.
In Kapitel 7 werden analog zu Kapitel 6 die Grundgleichungen der Magnetostatik hergeleitet. Die Übergangsbedingungen an Materialoberflächen werden diskutiert. Die Aussage, dass nach dem Helmholtzschen Zerlegungssatz (Hauptsatz der Vektoranalysis) ein gegebenes Vektorfeld eindeutig als Summe eines quellenfreien und eines wirbelfreien Anteils dargestellt werden kann, ist wesentlich in der Elektrodynamik. Der Satz wird formuliert und bewiesen. Weitere Themen des Kapitels sind u. a. die Induktion und verschiedene Formen des Magnetismus.
Ausgehend von den Maxwellschen Gleichungen im Vakuum werden im Kapitel 8 zunächst gekoppelte Differentialgleichungen für das skalare Potential \( \Phi \) und das Vektorpotential \( \vec{A} \) hergeleitet. Die Gleichungen entkoppeln sich, wenn sie der Lorentz-Bedingung genügen (Lorentz-Eichung genannt). Nach Einführung einiger Begriffe (Eichtransformation, Eichfunktion) wird schließlich gezeigt, dass die Eichfunktion der inhomogenen Wellengleichung genügt und dass zu jeder speziellen Wahl der Eichung, etwa auch der Coulomb-Eichung, zur Lösung der inhomogenen Gleichung die Lösung der homogenen Gleichung hinzugefügt werden kann. In der Coulomb-Eichung sind Quellen- und Wirbelanteile getrennt. Auf 110 Seiten werden anschließend noch die Lösung der homogenen Wellengleichung, Liénard-Wiechert-Potentiale, Fourierzerlegungen, Strahlungen bewegter Ladungsverteilungen, Dipol- und Quadrupolstrahlungen, Antennen und Strahlungsrückwirkungen analysiert.
In Kapitel 9 befassen sich die Autoren mit quasistationären Strömen. Es werden Systeme behandelt, in denen die elektrische Leitung auf aus dünnen Drähten bestehenden Leiterstrecken beschränkt ist. Die Leiterstrecken bestehen aus den Bauelementen eines elektrischen Netzwerkes (Widerstände, Induktivitäten, Kondensatoren und Spannungsquellen) und deren Verzweigungspunkten. Die zugehörigen Felder werden als langsam veränderlich betrachtet, das heißt, die charakteristische Zeit in einem System, multipliziert mit der Lichtgeschwindigkeit, ist viel kleiner als die Abmessung des Netzwerkes. Für die einzelnen Bestandteile des Netzwerkes werden quasistationäre Näherungen hergeleitet und so die zugehörigen Maxwellschen Gleichungen gewonnen. Die Themen Kirchhoffsche Regel, Maschenregel, Schwingungsgleichung, Gekoppelte Stromkreise, Wheatstone-Brücke, Signalübertragung mit Seekabeln, Telegraphengleichung seien u.a. genannt, um auf Folgerungen und Anwendungen in den weiteren Darstellungen hinzuweisen.
Im letzten Abschnitt des Kapitels wird die quasistationäre Näherung auf ionisierte Fluide (Plasmen) angewendet. Auch hier sind die zeitlichen Veränderungen, verglichen mit der Ausdehnung des Systems, langsam.
Zunächst werden die Grundgleichungen der Hydrodynamik formuliert, bestehend aus der Kontinuitätsgleichung mit der Bedingung für inkompressible Fluide und den Navier-Stokes-Gleichungen. Als Volumenkraft wird hier nur die Lorentz-Kraft berücksichtigt. Unter Vernachlässigung der Viskositäten ergibt sich die Eulersche Gleichung.
Auf Basis einiger Annahmen und Vernachlässigungen werden die zugehörigen Grundgleichungen der Elektrodynamik formuliert. Die entsprechende Euler-Gleichung ergibt sich schließlich aufgrund der Vernachlässigung des Terms \( \rho \vec{E} \) wegen \( |\vec{E}| \ll |\vec{B}| \). Für ruhendes Plasma (Hydrostatik) wird eine Diffusionsgleichung für das Magnetfeld hergeleitet. Für fließendes Plasma ergeben sich die hydrodynamischen Wellengleichungen, aus denen sich als Lösung transversale Wellen (sogenannte Alfvén-Wellen) bestimmen lassen, die sich mit einer Geschwindigkeit ausbreiten, die im Allgemeinen kleiner als die Schallgeschwindigkeit des Plasmas ist.
In Kapitel 10 werden elektromagnetische Wellen in verschiedenen Anwendungen analysiert. Im ersten Abschnitt wird die Wellengleichung für ebene Wellen (konstante Dielektrizitätskonstante und Permeabilität, Ladungsdichte \( \rho = 0 \) ) deduziert. Die partikulären Lösungen der Wellengleichung, die Fortpflanzungsrichtung, der zugehörige Poyntingvektor, die Energiedichte, Stokessche Parameter und monochromatisches Licht werden diskutiert.
Lineare, zirkulare und elliptische Polarisation und monochromatisches Licht sind Gegenstand des zweiten Abschnitts. Das Thema Reflektions- und Brechungsgesetz für Isolatoren umfasst das Brechungsgesetz von Snellius, Übergangsbedingungen für elektromagnetische Wellen unter Verwendung von Stetigkeitsbedingungen, Fresnelsche Formeln, Einfallsebene; Brewster-Winkel und Totalreflexion.
In der Geometrischen Optik (auch als Strahlenoptik bekannt) kann das monochromatische Licht durch ein skalares Wellenfeld beschrieben werden. Durch Einsetzen dieses Wellenfeldes in die Wellengleichung und Vernachlässigung der Variation der Amplitude ergibt sich die sogenannte Eikonalgleichung zur Berechnung des Strahls. Für die Ausbreitung des Strahls wird alternativ auch das Fermatsche Prinzip herangezogen. Außerdem werden Wellen in Leitern, Hohlraumresonatoren und Hohlleitern betrachtet (stehende Wellen, TE- und TM-Wellen).
Das Kapitel Röntgen-Streuung umfasst eine Vielzahl einzelner Themen, die hier nur skizziert werden. Im Abschnitt ``Streuung elektrischer Wellen'' werden die Thomson-Streuung, die Streuung an Elektronen (freie Elektronen, schwach gebundene Elektronen, Rayleigh-Streuung, Resonanzstreuung), die Streuung an einer Ladungsverteilung (Dispersionskorrekturen) und am Gitter (lineares Gitter, Bravais-Gitter) charakterisiert.
Im vorigen Abschnitt wurde angenommen, dass sich die Streuwellen ungehindert ausbreiten. In großen Idealkristallen müssen für die einfallenden und gebeugten Strahlen die Bewegungsgleichungen für die elektromagnetische Strahlung gelöst werden. Verfahren zur Lösung der fundamentalen Gleichungen werden behandelt. Als Anwendung der dynamischen Theorie wird die Beugung eines einfallenden Strahls an einer planparallelen Platte untersucht (Laue-Geometrie, Bragg-Geometrie).
Wie schon in den Ausführungen zu Kapitel 1 bemerkt, gelten für die klassische Mechanik und die Relativitätstheorie unterschiedliche Transformationsgesetze. Die Autoren beginnen daher zu Beginn des Kapitels 12 nach Einführung der Begriffe Inertialsystem und Relativgeschwindigkeit mit einer ausführlichen Diskussion des Universellen, des Galileischen (Relativitätsprinzip der klassischen Mechanik) und des Einsteinschen Relativitätsprinzips. In der Universellen Relativitätstheorie unterscheiden sich zwei Initialsysteme nur in der Relativgeschwindigkeit. In der Galileischen Relativitätstheorie sind die Zeitdifferenzen in allen Inertialsystemen und die räumlichen Abstände gleichzeitiger Ereignisse gleich. Das ist eine Einschränkung gegenüber der Universellen Theorie. In der Einsteinschen Theorie wird die Universelle Theorie durch die Gesetze der Elektrodynamik (etwa Wellengleichung) eingeschränkt. Die Wirkung der Transformationen auf die klassische Mechanik und die Elektrodynamik wird demonstriert. Die Eigenschaften der konstruierten Lorentztransformation werden diskutiert.
Anhand der historischen Entwicklung wird die Äthertheorie behandelt. Als Äther wurde zunächst ein Medium definiert, in dem sich das Licht ausbreitet. Die Autoren beschreiben Experimente und theoretische Überlegungen, die die Existenz eines ruhenden Äthers (Michelson-Morley-Experiment) als auch einer Äthermitführung widersprechen. Es wird dargelegt, dass aufgrund der Speziellen Relativitätstheorie ein Äther bei den beobachteten physikalischen Prozessen keine Rolle spielt.
Weitere Themen sind der Raum-Zeit-Begriff, die Synchronisation von Uhren, die Addition der Geschwindigkeiten, der Doppler-Effekt, die Lorentz-Kontraktion, die Zeitdilatation, die Eigenzeit und die Vierergeschwindigkeit.
Nach Einführung kovarianter Tensoren der Elektrodynamik werden die Maxwellschen Gleichungen unter Verwendung von Vierervektoren und Feldtensoren in kovarianter Form hergeleitet. Die Kovarianz wird bewiesen.
Im Kapitel 13, Relativistische Mechanik, werden für Gesetze der klassischen Mechanik, ausgehend von dem vorherigen Kapitel, kovariante Formen hergeleitet, das heißt, sie müssen umgeschrieben werden. Zunächst werden, ausgehend von der Geschwindigkeit, die kovarianten Vektoren für den Impuls, die Beschleunigung und die Lorentz-Kraft formuliert. Die Vierergeschwindigkeit ergibt sich unmittelbar aus der Annahme, dass in der relativistischen Mechanik, in der ein Körper ruht, unverändert die Gesetze der klassischen Mechanik gelten. Die Zeit in diesem System ist die sogenannte Eigenzeit, aus der gemäß Kapitel 12 die Vierergeschwindigkeit hergeleitet wurde. Durch Multiplikation mit der Masse erhält man auch den Viererimpuls. Auch die kovarianten Formen des Viererimpulses für Photonen, der Viererbeschleunigung und der Bewegungsgleichung werden erörtert. Weitere Themen betreffen die Abstrahlung in Linearbeschleunigern, die Linearbeschleunigung, das Synchrotron, die Strahlungsrückwirkung, die Lorentz-Gleichung, den Lagrange-Formalismus, das Hamilton-Prinzip, die elektromagnetischen Feldgleichungen, die Compton-Streuung und die Bewegung eines Elektrons um den Kern.
Abschließend sei gesagt, das mit diesem Buch nicht nur eine ausgezeichnete Publikation für Studenten der Physik und der Nachbargebiete vorliegt, sondern aufgrund der vielen ausführlichen Details auch ein Nachschlagwerk für Praktiker.
Reviewer: Georg Hebermehl (Berlin)A toy model for relativistic neutrino masseshttps://zbmath.org/1527.810752024-02-28T19:32:02.718555Z"Bruce, Stanley A."https://zbmath.org/authors/?q=ai:bruce.stanley-a(no abstract)Making relativistic quantum mechanics simplehttps://zbmath.org/1527.810762024-02-28T19:32:02.718555Z"de Peralta, Luis Grave"https://zbmath.org/authors/?q=ai:grave-de-peralta.luis"Poveda, Luis A."https://zbmath.org/authors/?q=ai:poveda.luis-a"Poirier, Bill"https://zbmath.org/authors/?q=ai:poirier.bill(no abstract)Holographic hadron masses in the language of quantum mechanicshttps://zbmath.org/1527.810992024-02-28T19:32:02.718555Z"Domokos, S. K."https://zbmath.org/authors/?q=ai:domokos.sophia-k"Bell, R."https://zbmath.org/authors/?q=ai:bell.robert-a|bell.robert-james|bell.rayna|bell.r-c|bell.robert-i|bell.ronald-p|bell.ralf|bell.renee|bell.robert-w|bell.rod-d|bell.robert-m|bell.rowen-b|bell.renelius"La, T."https://zbmath.org/authors/?q=ai:la.t"Mazza, P."https://zbmath.org/authors/?q=ai:mazza.paolo-p(no abstract)Equilibrium states for the massive sine-Gordon theory in the Lorentzian signaturehttps://zbmath.org/1527.811002024-02-28T19:32:02.718555Z"Bahns, Dorothea"https://zbmath.org/authors/?q=ai:bahns.dorothea"Pinamonti, Nicola"https://zbmath.org/authors/?q=ai:pinamonti.nicola"Rejzner, Kasia"https://zbmath.org/authors/?q=ai:rejzner.katarzynaSummary: In this paper we investigate the massive Sine-Gordon model in the ultraviolet finite regime in thermal states over the two-dimensional Minkowski spacetime. We combine recently developed methods of perturbative algebraic quantum field theory with techniques developed in the realm of constructive quantum field theory over Euclidean spacetimes to construct the correlation functions of the equilibrium state of the Sine-Gordon theory in the adiabatic limit. First of all, the observables of the Sine-Gordon theory are seen as functionals over the free configurations and are obtained as a suitable combination of the \(S\)-matrices of the interaction Lagrangian restricted to compact spacetime regions over the free massive theory. These \(S\)-matrices are given as power series in the coupling constant with values in the algebra of fields over the free massive theory. Adapting techniques like conditioning and inverse conditioning to spacetimes with Lorentzian signature, we prove that these power series converge when evaluated on a generic field configuration. The latter observation implies convergence in the strong operator topology in the GNS representations of the considered states. In the second part of the paper, adapting the cluster expansion technique to the Lorentzian case, we prove that the correlation functions of the interacting equilibrium state at finite temperature (KMS state) can be constructed also in the adiabatic limit, where the interaction Lagrangian is supported everywhere in space.GINGERhttps://zbmath.org/1527.830012024-02-28T19:32:02.718555Z"Altucci, Carlo"https://zbmath.org/authors/?q=ai:altucci.carlo"Bajardi, Francesco"https://zbmath.org/authors/?q=ai:bajardi.francesco"Barchiesi, Emilio"https://zbmath.org/authors/?q=ai:barchiesi.emilio"Basti, Andrea"https://zbmath.org/authors/?q=ai:basti.andrea"Beverini, Nicolò"https://zbmath.org/authors/?q=ai:beverini.nicolo"Braun, Thomas"https://zbmath.org/authors/?q=ai:braun.thomas-m|braun.thomas-r"Carelli, Giorgio"https://zbmath.org/authors/?q=ai:carelli.giorgio"Capozziello, Salvatore"https://zbmath.org/authors/?q=ai:capozziello.salvatore"Castellano, Simone"https://zbmath.org/authors/?q=ai:castellano.simone"Ciampini, Donatella"https://zbmath.org/authors/?q=ai:ciampini.donatella"Davì, Fabrizio"https://zbmath.org/authors/?q=ai:davi.fabrizio"De Luca, Gaetano"https://zbmath.org/authors/?q=ai:de-luca.gaetano"Devoti, Roberto"https://zbmath.org/authors/?q=ai:devoti.roberto"Di Giovambattista, Rita"https://zbmath.org/authors/?q=ai:di-giovambattista.rita"Di Somma, Giuseppe"https://zbmath.org/authors/?q=ai:di-somma.giuseppe"Di Stefano, Giuseppe"https://zbmath.org/authors/?q=ai:di-stefano.giuseppe"Di Virgilio, Angela D. V."https://zbmath.org/authors/?q=ai:di-virgilio.angela-d-v"Famiani, Daniela"https://zbmath.org/authors/?q=ai:famiani.daniela"Frepoli, Alberto"https://zbmath.org/authors/?q=ai:frepoli.alberto"Fuso, Francesco"https://zbmath.org/authors/?q=ai:fuso.francesco"Giorgio, Ivan"https://zbmath.org/authors/?q=ai:giorgio.ivan"Govoni, Aladino"https://zbmath.org/authors/?q=ai:govoni.aladino"Lambiase, Gaetano"https://zbmath.org/authors/?q=ai:lambiase.gaetano"Maccioni, Enrico"https://zbmath.org/authors/?q=ai:maccioni.enrico"Marsili, Paolo"https://zbmath.org/authors/?q=ai:marsili.paolo"Mercuri, Alessia"https://zbmath.org/authors/?q=ai:mercuri.alessia"Morsani, Fabio"https://zbmath.org/authors/?q=ai:morsani.fabio"Ortolan, Antonello"https://zbmath.org/authors/?q=ai:ortolan.antonello"Porzio, Alberto"https://zbmath.org/authors/?q=ai:porzio.alberto"Ruggiero, Matteo Luca"https://zbmath.org/authors/?q=ai:ruggiero.matteo-luca"Tallini, Marco"https://zbmath.org/authors/?q=ai:tallini.marco"Tasson, Jay"https://zbmath.org/authors/?q=ai:tasson.jay"Turco, Emilio"https://zbmath.org/authors/?q=ai:turco.emilio"Velotta, Raffaele"https://zbmath.org/authors/?q=ai:velotta.raffaeleSummary: We outline the scientific objectives, the experimental layout, and the collaborations envisaged for the GINGER (\emph{Gyroscopes in general relativity}) project. The GINGER project brings together different scientific disciplines aiming at building an array of ring laser gyroscopes (RLGs), exploiting the Sagnac effect, to measure continuously, with sensitivity better than pico-rad/s, large bandwidth (ca. 1\,kHz), and high dynamic range, the absolute angular rotation rate of Earth. We address the feasibility of the apparatus with respect to the ambitious specifications above, as well as prove how such an apparatus, which will be able to detect strong earthquakes, very weak geodetic signals, as well as general relativity effects like Lense-Thirring and de Sitter, will help scientific advancements in theoretical physics, geophysics, and geodesy, among other scientific fields.Order topology in Minkowski space and applicationshttps://zbmath.org/1527.830022024-02-28T19:32:02.718555Z"Koumantos, Panagiotis N."https://zbmath.org/authors/?q=ai:koumantos.panagiotis-nSummary: In this article, we consider and study the order topology in Minkowski spacetime of the special theory of relativity, \textit{i.e.} the finest locally convex topology \(\tau\) on spacetime for which every order bounded subset of spacetime is \(\tau\)-bounded. This order topology that is introduced into spacetime as an ordered vector space proves to be Hausdorff and differs from Zeeman's order topology. Applying the order topology we obtain new results by applying and extending previous results on the mean ergodic theorem and functional differential evolution equations in the Minkowski space.Complete super-sample lensing covariance in the response approachhttps://zbmath.org/1527.830032024-02-28T19:32:02.718555Z"Barreira, Alexandre"https://zbmath.org/authors/?q=ai:barreira.alexandre"Krause, Elisabeth"https://zbmath.org/authors/?q=ai:krause.elisabeth"Schmidt, Fabian"https://zbmath.org/authors/?q=ai:schmidt.fabianSummary: We derive the complete super-sample covariance (SSC) of the matter and weak lensing convergence power spectra using the power spectrum response formalism to accurately describe the coupling of super- to sub-survey modes. The SSC term is completely characterized by the survey window function, the nonlinear matter power spectrum and the full first-order nonlinear power spectrum response function, which describes the response to super-survey density and tidal field perturbations. Generalized separate universe simulations can efficiently measure these responses in the nonlinear regime of structure formation, which is necessary for lensing applications. We derive the lensing SSC formulae for two cases: one under the Limber and flat-sky approximations, and a more general one that goes beyond the Limber approximation in the super-survey mode and is valid for curved sky applications. Quantitatively, we find that for sky fractions \(f_{\mathrm{sky}} \approx 0.3\) and a single source redshift at \(z_S=1\), the use of the flat-sky and Limber approximation underestimates the total SSC contribution by \(\approx 10\)\%. The contribution from super-survey tidal fields to the lensing SSC, which has not been included in cosmological analyses so far, is shown to represent about 5\% of the total lensing covariance on multipoles \(\ell_1, \ell_2 \gtrsim 300\). The SSC is the dominant off-diagonal contribution to the total lensing covariance, making it appropriate to include these tidal terms and beyond flat-sky/Limber corrections in cosmic shear analyses.Weak lensing probe of cubic Galileon modelhttps://zbmath.org/1527.830042024-02-28T19:32:02.718555Z"Dinda, Bikash R."https://zbmath.org/authors/?q=ai:dinda.bikash-rSummary: The cubic Galileon model containing the lowest non-trivial order action of the full Galileon action can produce the stable late-time cosmic acceleration. This model can have a significant role in the growth of structures. The signatures of the cubic Galileon model in the structure formation can be probed by the weak lensing statistics. Weak lensing convergence statistics is one of the strongest probes to the structure formation and hence it can probe the dark energy or modified theories of gravity models. In this work, we investigate the detectability of the cubic Galileon model from the \(\Lambda\)CDM model or from the canonical quintessence model through the convergence power spectrum and bi-spectrum.General relativistic corrections in density-shear correlationshttps://zbmath.org/1527.830052024-02-28T19:32:02.718555Z"Ghosh, Basundhara"https://zbmath.org/authors/?q=ai:ghosh.basundhara"Durrer, Ruth"https://zbmath.org/authors/?q=ai:durrer.ruth"Sellentin, Elena"https://zbmath.org/authors/?q=ai:sellentin.elenaSummary: We investigate the corrections which relativistic light-cone computations induce on the correlation of the tangential shear with galaxy number counts, also known as galaxy-galaxy lensing. The standard-approach to galaxy-galaxy lensing treats the number density of sources in a foreground bin as observable, whereas it is in reality unobservable due to the presence of relativistic corrections. We find that already in the redshift range covered by the DES first year data, these currently neglected relativistic terms lead to a systematic correction of up to 50\% in the density-shear correlation function for the highest redshift bins. This correction is dominated by the fact that a redshift bin of number counts does not only lens sources in a background bin, but is itself again lensed by all masses between the observer and the counted source population. Relativistic corrections are currently ignored in the standard galaxy-galaxy analyses, and the additional lensing of a counted source populations is only included in the error budget (via the covariance matrix). At increasingly higher redshifts and larger scales, these relativistic and lensing corrections become however increasingly more important, and we here argue that it is then more efficient, and also cleaner, to account for these corrections in the density-shear correlations.Jacobi mapping approach for a precise cosmological weak lensing formalismhttps://zbmath.org/1527.830062024-02-28T19:32:02.718555Z"Grimm, Nastassia"https://zbmath.org/authors/?q=ai:grimm.nastassia"Yoo, Jaiyul"https://zbmath.org/authors/?q=ai:yoo.jaiyulSummary: Cosmological weak lensing has been a highly successful and rapidly developing research field since the first detection of cosmic shear in 2000. However, it has recently been pointed out in Yoo et al. that the standard weak lensing formalism yields gauge-dependent results and, hence, does not meet the level of accuracy demanded by the next generation of weak lensing surveys. Here, we show that the Jacobi mapping formalism provides a solid alternative to the standard formalism, as it accurately describes all the relativistic effects contributing to the weak lensing observables. We calculate gauge-invariant expressions for the distortion in the luminosity distance, the cosmic shear components and the lensing rotation to linear order including scalar, vector and tensor perturbations. In particular, the Jacobi mapping formalism proves that the rotation is fully vanishing to linear order. Furthermore, the cosmic shear components contain an additional term in tensor modes which is absent in the results obtained with the standard formalism. Our work provides further support and confirmation of the gauge-invariant lensing formalism needed in the era of precision cosmology.Real space lensing reconstruction using cosmic microwave background polarizationhttps://zbmath.org/1527.830072024-02-28T19:32:02.718555Z"Prince, Heather"https://zbmath.org/authors/?q=ai:prince.heather"Moodley, Kavilan"https://zbmath.org/authors/?q=ai:moodley.kavilan"Ridl, Jethro"https://zbmath.org/authors/?q=ai:ridl.jethro"Bucher, Martin"https://zbmath.org/authors/?q=ai:bucher.martinSummary: We develop a method of reconstructing the lensing field from lensed CMB temperature and polarization maps in real space as an alternative to the harmonic space estimators currently in use by extending an existing real space lensing estimator for temperature to polarization. Real space estimators have the advantage of being local in nature and they are thus equipped to deal with the nonuniform sky coverage, especially galactic cuts and point source excisions, found in experimental data. We characterize some of the properties and limitations of these estimators and test them on simulated maps with Planck, AdvACT and CMB-S4 noise. We show that the reconstructions for large-scale lensing fields are accurate, and that the polarization reconstructions improve on those from CMB temperature maps for future experiments as expected. High-fidelity lensing maps can be reconstructed with futuristic experiments like CMB-S4.On the conformal method for the Einstein constraint equationshttps://zbmath.org/1527.830082024-02-28T19:32:02.718555Z"Anderson, Michael T."https://zbmath.org/authors/?q=ai:anderson.michael-tSummary: In this work, we use the global analysis and degree-theoretic methods introduced by Smale to study the existence and multiplicity of solutions of the vacuum Einstein constraint equations given by the conformal method of Lichnerowicz-Choquet-Bruhat-York. In particular this approach gives a new proof of the existence result of Maxwell and Holst-Nagy-Tsogtgerel. We also relate the method to the limit equation of Dahl-Gicquaud-Humbert and the nonexistence result of Nguyen.A new bifurcation in the universehttps://zbmath.org/1527.830092024-02-28T19:32:02.718555Z"Hartmann, A. E. S."https://zbmath.org/authors/?q=ai:hartmann.a-e-s"Novello, M."https://zbmath.org/authors/?q=ai:novello.marco|novello.marioSummary: The combined system of general relativity with a non-minimally coupled electromagnetic field presents a bifurcation in a cosmic framework. In order to simplify our exposition in this chapter, we limit the proof to the case of an universe driven by a cosmological constant. In the same vein, we show the existence of states such that the resulting combined energy (the sum of the minimally and the non-minimally coupled energy momentum tensor of the electromagnetic field) vanishes in a sort of violation of the action-reaction principle.
For the entire collection see [Zbl 1448.68036].Dimensional analysis in relativity and in differential geometryhttps://zbmath.org/1527.830102024-02-28T19:32:02.718555Z"Mana, P. G. L. Porta"https://zbmath.org/authors/?q=ai:mana.p-g-l-porta(no abstract)Twisted self-similarity and the Einstein vacuum equationshttps://zbmath.org/1527.830112024-02-28T19:32:02.718555Z"Shlapentokh-Rothman, Yakov"https://zbmath.org/authors/?q=ai:shlapentokh-rothman.yakovSummary: In the previous works \textit{I. Rodnianski} and \textit{Y. Shlapentokh-Rothman} [``Naked singularities for the Einstein vacuum equations: the exterior solution'', Preprint, \url{arXiv:1912.08478}] and \textit{Y. Shlapentokh-Rothman} [``Naked singularities for the Einstein vacuum equations: the interior solution'', Preprint \url{arXiv:2204.09891}] we have introduced a new type of self-similarity for the Einstein vacuum equations characterized by the fact that the homothetic vector field may be spacelike on the past light cone of the singularity. In this work we give a systematic treatment of this new self-similarity. In particular, we provide geometric characterizations of spacetimes admitting the new symmetry and show the existence and uniqueness of formal expansions around the past null cone of the singularity which may be considered analogues of the well-known Fefferman-Graham expansions. In combination with results from Rodnianski and Shlapentokh-Rothman [loc. cit.] our analysis will show that the twisted self-similar solutions are sufficiently general to describe all possible asymptotic behaviors for spacetimes in the small data regime which are self-similar and whose homothetic vector field is everywhere spacelike on an initial spacelike hypersurface. We present an application of this later fact to the understanding of the global structure of Fefferman-Graham spacetimes and the naked singularities of Rodnianski and Shlapentokh-Rothman [loc. cit.] and Shlapentokh-Rothman [loc. cit.]. Lastly, we observe that by an amalgamation of the techniques from \textit{I. Rodnianski} and \textit{Y. Shlapentokh-Rothman} [Geom. Funct. Anal. 28, No. 3, 755--878 (2018; Zbl 1394.35501)], one may associate true solutions to the Einstein vacuum equations to each of our formal expansions in a suitable region of spacetime.Derivation of generalized Einstein's equations of gravitation in some noninertial reference frames based on the theory of vacuum mechanicshttps://zbmath.org/1527.830122024-02-28T19:32:02.718555Z"Wang, Xiao-Song"https://zbmath.org/authors/?q=ai:wang.xiaosongSummary: When solving Einstein's equations for an isolated system of masses, V. Fock introduced a harmonic reference frame and obtained an unambiguous solution. Further, he concluded that there existed a harmonic reference frame which was determined uniquely apart from a Lorentz transformation if suitable supplementary conditions were imposed. It is known that wave equations keep the same form under Lorentz transformations. Thus, we speculate that Fock's special harmonic reference frames may provide us with a clue to derive Einstein's equations in some special class of noninertial reference frames. Following this idea, generalized Einstein's equations in some special noninertial reference frames are derived based on the theory of vacuum mechanics. If the field is weak and the reference frame is quasi-inertial, these generalized Einstein's equations reduce to Einstein's equations. Thus, this theory may also explain all the experiments which support the theory of general relativity. There exist some differences between this theory and the theory of general relativity.Traveling wave and general form solutions for the coupled Higgs systemhttps://zbmath.org/1527.830132024-02-28T19:32:02.718555Z"Duran, Serbay"https://zbmath.org/authors/?q=ai:duran.serbay"Durur, Hülya"https://zbmath.org/authors/?q=ai:durur.hulya"Yokuş, Asıf"https://zbmath.org/authors/?q=ai:yokus.asif(no abstract)An exact solution for a rotating black hole in modified gravityhttps://zbmath.org/1527.830142024-02-28T19:32:02.718555Z"Filippini, Francesco"https://zbmath.org/authors/?q=ai:filippini.francesco"Tasinato, Gianmassimo"https://zbmath.org/authors/?q=ai:tasinato.gianmassimoSummary: Exact solutions describing rotating black holes can offer important tests for alternative theories of gravity, motivated by the dark energy and dark matter problems. We present an analytic rotating black hole solution for a class of vector-tensor theories of modified gravity, valid for arbitrary values of the rotation parameter. The new configuration is characterised by parametrically large deviations from the Kerr-Newman geometry, controlled by non-minimal couplings between vectors and gravity. It has an oblate horizon in Boyer-Lindquist coordinates, and it can rotate more rapidly and have a larger ergosphere than black holes in General Relativity (GR) with the same asymptotic properties. We analytically investigate the features of the innermost stable circular orbits for massive objects on the equatorial plane, and show that stable orbits lie further away from the black hole horizon with respect to rotating black holes in GR. We also comment on possible applications of our findings for the extraction of rotational energy from the black hole.Strong field lensing by Damour-Solodukhin wormholehttps://zbmath.org/1527.830152024-02-28T19:32:02.718555Z"Nandi, K. K."https://zbmath.org/authors/?q=ai:nandi.kamal-kanti"Izmailov, R. N."https://zbmath.org/authors/?q=ai:izmailov.ramil-nailevich"Zhdanov, E. R."https://zbmath.org/authors/?q=ai:zhdanov.e-r"Bhattacharya, Amrita"https://zbmath.org/authors/?q=ai:bhattacharya.amritaSummary: We investigate the strong field lensing observables for the Damour-Soludukhin wormhole and examine how small the values of the deviation parameter \(\lambda\) need be for reproducing the observables for the Schwarzschild black hole. While the extremely tiny values of \(\lambda\) indicated by the matter accretion or Hawking evaporation are quite consistent with the lensing observations, it turns out that \(\lambda\) could actually assume values considerably higher values and still reproduce black hole lensing signatures. The lensing observables for SgrA* can be interpreted to provide an upper bound on \(\lambda \sim 10^{-3}\) and until lower bound is established, all values of \(\lambda\) below the upper bound should be treated as equally probable.Isomorphism between the local Poincaré generalized translations group and the group of spacetime transformations \((\otimes\mathrm{LB}1)^4\)https://zbmath.org/1527.830162024-02-28T19:32:02.718555Z"Garat, Alcides"https://zbmath.org/authors/?q=ai:garat.alcidesSummary: We will prove that there is a direct relationship between the Poincaré subgroup of translations, and the group of tetrad transformations LB1 introduced in a previous paper. LB1 is the group composed of \(\mathrm{SO}(1, 1)\) plus two kinds of discrete transformations. Translations have been extensively studied under the scope of gauge theories. By using the geometric structures built to prove this elementary result we will generalize it to the case of what we might call local translations. A special case of the latter is the Bondi-Metzner-Sachs subgroup of supertranslations. In order to accomplish this goal and since the group of translations is four-dimensional we will prove first that it is isomorphic to \((\otimes\mathrm{LB}1)^4\). In order to prove this claim we will introduce a system of differential equations involving several kinds of fields -- abelian, non-abelian, spinor, gravitational. These fields will constitute the structure needed to build local tetrads of a new kind that allow for the proof to be carried out with simplicity. Results already obtained involving similar but not equal tetrads will be useful in our constructions and demonstrations. Translations and generalized translations isomorphic to tensor products of LB1 groups are not trivial results, because the LB1 group is composed of \(\mathrm{SO}(1, 1)\) and two discrete transformationsOn the motion of hairy black holes in Einstein-Maxwell-dilaton theorieshttps://zbmath.org/1527.830172024-02-28T19:32:02.718555Z"Julié, Félix-Louis"https://zbmath.org/authors/?q=ai:julie.felix-louisSummary: Starting from the static, spherically symmetric black hole solutions in massless Einstein-Maxwell-dilaton (EMD) theories, we build a ``skeleton'' action, that is, we phenomenologically replace black holes by an appropriate effective point particle action, which is well suited to the formal treatment of the many-body problem in EMD theories. We find that, depending crucially on the value of their scalar cosmological environment, black holes can undergo steep ``scalarization'' transitions, inducing large deviations to the general relativistic two-body dynamics, as shown, for example, when computing the first post-Keplerian Lagrangian of EMD theories.Traversable wormholes in four dimensionshttps://zbmath.org/1527.830182024-02-28T19:32:02.718555Z"Maldacena, Juan"https://zbmath.org/authors/?q=ai:maldacena.juan-m.1"Milekhin, Alexey"https://zbmath.org/authors/?q=ai:milekhin.alexey"Popov, Fedor"https://zbmath.org/authors/?q=ai:popov.fedor-kSummary: We present a wormhole solution in four dimensions. It is a solution of an Einstein Maxwell theory plus charged massless fermions. The fermions give rise to a negative Casimir-like energy, which makes the wormhole possible. It is a long wormhole that does not lead to causality violations in the ambient space. It can be viewed as a pair of entangled near extremal black holes with an interaction term generated by the exchange of fermion fields. The solution can be embedded in the Standard Model by making its overall size small compared to the electroweak scale.Hydrodynamic consequences of Vlasov-Maxwell-Einstein equations and their cosmological applicationshttps://zbmath.org/1527.830192024-02-28T19:32:02.718555Z"Vedenyapin, V. V."https://zbmath.org/authors/?q=ai:vedenyapin.victor-v"Fimin, N. N."https://zbmath.org/authors/?q=ai:fimin.nikolai-nikolaevich"Chechetkin, V. M."https://zbmath.org/authors/?q=ai:chechetkin.valerii-mikhailovichSummary: The paper proposes and implements a method of obtaining a closed set of Vlasov-Maxwell-Einstein equations (and its weakly relativistic and nonrelativistic analogues) based on variation of the generalized Hilbert-Einstein-Pauli action. This technique also makes it possible to obtain the exact form of the energy-momentum tensor in terms of particle distribution functions. Using a hydrodynamic substitution in the Vlasov equation, the Euler-Lamb equations are obtained, which can be transformed to the form of Hamilton-Jacobi equations. Exact solutions of cosmological type of the hydrodynamic system are demonstrated, and their physical consequences are analyzed (including a generalization of the Milne-McCrea model).Gauge fixing and regularity of axially symmetric and axistationary second order perturbations around spherical backgroundshttps://zbmath.org/1527.830202024-02-28T19:32:02.718555Z"Mars, Marc"https://zbmath.org/authors/?q=ai:mars.marc"Reina, Borja"https://zbmath.org/authors/?q=ai:reina.borja"Vera, Raül"https://zbmath.org/authors/?q=ai:vera.raulSummary: Perturbation theory in geometric theories of gravitation is a gauge theory of symmetric tensors defined on a Lorentzian manifold (the background spacetime). The gauge freedom makes uniqueness problems in perturbation theory particularly hard as one needs to understand in depth the process of gauge fixing before attempting any uniqueness proof. This is the first paper of a series of two aimed at deriving an existence and uniqueness result for rigidly rotating stars to second order in perturbation theory in General Relativity. A necessary step is to show the existence of a suitable choice of gauge and to understand the differentiability and regularity properties of the resulting gauge tensors in some ``canonical form'', particularly at the centre of the star. With a wider range of applications in mind, in this paper we analyse the gauge fixing and regularity problem in a more general setting. In particular we tackle the problem of the Hodge-type decomposition into scalar, vector and tensor components on spheres of symmetric and axially symmetric tensors with finite differentiability down to the origin, exploiting a strategy in which the loss of differentiability is as low as possible. Our primary interest, and main result, is to show that stationary and axially symmetric second order perturbations around static and spherically symmetric background configurations can indeed be rendered in the usual ``canonical form'' used in the literature while losing \textit{only} one degree of differentiability and keeping all relevant quantities bounded near the origin.Evaluating quasi-local angular momentum and center-of-mass at null infinityhttps://zbmath.org/1527.830212024-02-28T19:32:02.718555Z"Keller, Jordan"https://zbmath.org/authors/?q=ai:keller.jordan"Wang, Ye-Kai"https://zbmath.org/authors/?q=ai:wang.ye-kai"Yau, Shing-Tung"https://zbmath.org/authors/?q=ai:yau.shing-tungSummary: We calculate the limits of the quasi-local angular momentum and center-of-mass defined by \textit{P.-N. Chen} et al. [Commun. Math. Phys. 338, No. 1, 31--80 (2015; Zbl 1319.83011)] for a family of spacelike two-spheres approaching future null infinity in an asymptotically flat spacetime admitting a Bondi-Sachs expansion. Our result complements earlier work of \textit{P. Chen} et al. [Commun. Math. Phys. 308, No. 3, 845--863 (2011; Zbl 1269.83024)], where the authors calculate the limits of the quasi-local energy and linear momentum at null infinity. Finiteness of the center-of-mass limit requires that the spacetime be in the so-called center-of-mass frame, a mild assumption on the mass aspect function amounting to vanishing of linear momentum at null infinity. With this condition and the assumption that the Bondi mass is non-trivial, we obtain explicit expressions for the angular momentum and center-of-mass at future null infinity in terms of the observables appearing in the Bondi-Sachs expansion of the spacetime metric.Spin Hall effects in the skyhttps://zbmath.org/1527.830222024-02-28T19:32:02.718555Z"Andersson, Lars"https://zbmath.org/authors/?q=ai:andersson.lars-ake|andersson.lars-erik|andersson.lars-l"Oancea, Marius A."https://zbmath.org/authors/?q=ai:oancea.marius-aSummary: In many areas of physics, the propagation of wave packets carrying intrinsic angular momentum is generally influenced by spin-orbit interactions. This is the main mechanism behind spin Hall effects, which result in wave packets following spin-dependent trajectories. Spin Hall effects have been observed in several experiments for electrons in condensed matter systems and for light propagating in inhomogeneous optical media. Similar effects have also been predicted for wave packets propagating in inhomogeneous gravitational fields. We give a brief introduction to gravitational spin Hall effects, emphasizing the analogies with the spin Hall effect of light in optics. Furthermore, we review the most promising astrophysical avenues that could lead to experimental observations of the gravitational spin Hall effect.Probing non-Gaussian stochastic gravitational wave backgrounds with LISAhttps://zbmath.org/1527.830232024-02-28T19:32:02.718555Z"Bartolo, Nicola"https://zbmath.org/authors/?q=ai:bartolo.nicola"Domcke, Valerie"https://zbmath.org/authors/?q=ai:domcke.valerie"Figueroa, Daniel G."https://zbmath.org/authors/?q=ai:figueroa.daniel-g"Garcia-Bellido, Juan"https://zbmath.org/authors/?q=ai:garcia-bellido.juan"Peloso, Marco"https://zbmath.org/authors/?q=ai:peloso.marco"Pieroni, Mauro"https://zbmath.org/authors/?q=ai:pieroni.mauro"Ricciardone, Angelo"https://zbmath.org/authors/?q=ai:ricciardone.angelo.1"Sakellariadou, Mairi"https://zbmath.org/authors/?q=ai:sakellariadou.mairi"Sorbo, Lorenzo"https://zbmath.org/authors/?q=ai:sorbo.lorenzo"Tasinato, Gianmassimo"https://zbmath.org/authors/?q=ai:tasinato.gianmassimoSummary: The stochastic gravitational wave background (SGWB) contains a wealth of information on astrophysical and cosmological processes. A major challenge of upcoming years will be to extract the information contained in this background and to disentangle the contributions of different sources. In this paper we provide the formalism to extract, from the correlation of three signals in the Laser Interferometer Space Antenna (LISA), information about the tensor three-point function, which characterizes the non-Gaussian properties of the SGWB. This observable can be crucial to discriminate whether a SGWB has a primordial or astrophysical origin. Compared to the two-point function, the SGWB three-point function has a richer dependence on the gravitational wave momenta and chiralities. It can be used therefore as a powerful discriminator between different models. For the first time we provide the response functions of LISA to a general SGWB three-point function. As examples, we study in full detail the cases of an equilateral and squeezed SGWB bispectra, and provide the explicit form of the response functions, ready to be convoluted with any theoretical prediction of the bispectrum to obtain the observable signal. We further derive the optimal estimator to compute the signal-to-noise ratio. Our formalism covers general shapes of non-Gaussianity, and can be extended straightaway to other detector geometries. Finally, we provide a short overview of models of the early universe that can give rise to a non-Gaussian SGWB.Back-reaction of gravitational waves revisitedhttps://zbmath.org/1527.830242024-02-28T19:32:02.718555Z"Brandenberger, Robert"https://zbmath.org/authors/?q=ai:brandenberger.robert-h"Takahashi, Tomo"https://zbmath.org/authors/?q=ai:takahashi.tomoSummary: We study the back-reaction of gravitational waves in early universe cosmology, focusing both on super-Hubble and sub-Hubble modes. Sub-Hubble modes lead to an effective energy density which scales as radiation. Hence, the relative contribution of such gravitational waves to the total energy density is constrained by big bang nucleosynthesis. This leads to an upper bound on the tensor spectral slope \(n_T\) which also depends on the tensor to scalar ratio \(r\). Super-Hubble modes, on the other hand, lead to a negative contribution to the effective energy density, and to an equation of state of curvature. Demanding that the early universe is not dominated by the back-reaction leads to constraints on the gravitational wave spectral parameters which are derived.A cosmological signature of the SM Higgs instability: gravitational waveshttps://zbmath.org/1527.830252024-02-28T19:32:02.718555Z"Espinosa, J. R."https://zbmath.org/authors/?q=ai:espinosa.jose-r"Racco, D."https://zbmath.org/authors/?q=ai:racco.d"Riotto, A."https://zbmath.org/authors/?q=ai:riotto.a.1Summary: A fundamental property of the Standard Model is that the Higgs potential becomes unstable at large values of the Higgs field. For the current central values of the Higgs and top masses, the instability scale is about \(10^{11}\) GeV and therefore not accessible by colliders. We show that a possible signature of the Standard Model Higgs instability is the production of gravitational waves sourced by Higgs fluctuations generated during inflation. We fully characterise the two-point correlator of such gravitational waves by computing its amplitude, the frequency at peak, the spectral index, as well as their three-point correlators for various polarisations. We show that, depending on the Higgs and top masses, either LISA or the Einstein Telescope and Advanced-Ligo, could detect such stochastic background of gravitational waves. In this sense, collider and gravitational wave physics can provide fundamental and complementary informations. Furthermore, the consistency relation among the three- and the two-point correlators could provide an efficient tool to ascribe the detected gravitational waves to the Standard Model itself. Since the mechanism described in this paper might also be responsible for the generation of dark matter under the form of primordial black holes, this latter hypothesis may find its confirmation through the detection of gravitational waves.Primordial gravitational waves and perturbations during an inhomogeneous inflationhttps://zbmath.org/1527.830262024-02-28T19:32:02.718555Z"Gao, Xian"https://zbmath.org/authors/?q=ai:gao.xian"Kang, Chao"https://zbmath.org/authors/?q=ai:kang.chaoSummary: We investigate the inhomogeneous inflation, in which the space exponentially expands with inhomogeneities, and its cosmological perturbations. The inhomogeneous inflation is realized by introducing scalar fields with spacelike gradients that break the spatial symmetry. We find that the space can expand uniformly in different direction with the same rate. By using the perturbative method, we calculate the corrections to the power spectra of gravitational waves and curvature perturbation up to the linear order in the background inhomogeneities. Since the background is inhomogeneous, perturbations modes with different wave numbers get correlated. We show that generally the power spectra of perturbations depend on the ratio and the angle of wave numbers of the two correlated modes. In particular, the two circular polarization modes of the gravitational waves gain different powers when the background inhomogeneity is of vector or tensor type.Massive gravity and the suppression of anisotropies and gravitational waves in a matter-dominated contracting universehttps://zbmath.org/1527.830272024-02-28T19:32:02.718555Z"Lin, Chunshan"https://zbmath.org/authors/?q=ai:lin.chunshan"Quintin, Jerome"https://zbmath.org/authors/?q=ai:quintin.jerome"Brandenberger, Robert H."https://zbmath.org/authors/?q=ai:brandenberger.robert-hSummary: We consider a modified gravity model with a massive graviton, but which nevertheless only propagates two gravitational degrees of freedom and which is free of ghosts. We show that non-singular bouncing cosmological background solutions can be generated. In addition, the mass term for the graviton prevents anisotropies from blowing up in the contracting phase and also suppresses the spectrum of gravitational waves compared to that of the scalar cosmological perturbations. This addresses two of the main problems of the \textit{matter bounce} scenario.Observable chiral gravitational waves from inflation in string theoryhttps://zbmath.org/1527.830282024-02-28T19:32:02.718555Z"McDonough, Evan"https://zbmath.org/authors/?q=ai:mcdonough.evan"Alexander, Stephon"https://zbmath.org/authors/?q=ai:alexander.stephon-h-sSummary: We consider gravitational wave production during inflation in type IIB string theory, and the possibility of observable gravitational waves in small field inflation. We show that the gauge field excitations on a set of coincident D7 branes, itself critical for moduli stabilization and hence intrinsic to inflation in string theory, coupled with axion fields from bulk fluxes, can act as a spectator sector during inflation. This results in a large production of chiral gravitational waves, even for relatively small values of the axion-gauge field coupling. We extend this to include a monodromy for the axion, and demonstrate that in both cases an observable level of gravitational waves is produced in small field inflation in string theory, with a spectrum that is maximally chiral. Finally, we demonstrate the consistency with moduli stabilization and with arbitrary (large or small field) inflationary dynamics of the host model, considering as an explicit example Kahler Moduli Inflation.Circularly polarized EM radiation from GW binary sourceshttps://zbmath.org/1527.830292024-02-28T19:32:02.718555Z"Shakeri, Soroush"https://zbmath.org/authors/?q=ai:shakeri.soroush"Allahyari, Alireza"https://zbmath.org/authors/?q=ai:allahyari.alirezaSummary: We consider the polarization characteristics of the electromagnetic (EM) counterpart of the gravitational wave (GW) created by coalescence of the binary sources. Here, we explore the impact of the photon-graviton interaction on the polarization evolution of X-ray emission of Gamma-Ray Bursts (GRBs). We show that significant circular polarization can be generated due to the gravitational wave from the binary merger. The circular polarization besides photon energy depends on parameters of GW source such as the chirp mass of the binary, frequency of the GWs and radial distance from the source. Our predicted signal can be used as an indirect probe for GW events and also the nature of photon-graviton interaction. We argue that this polarization signal might be in sensitivity range of upcoming X-ray polarimetry missions.Post-Newtonian-accurate pulsar timing array signals induced by inspiralling eccentric binaries: accuracy, computational cost, and single-pulsar searchhttps://zbmath.org/1527.830302024-02-28T19:32:02.718555Z"Susobhanan, Abhimanyu"https://zbmath.org/authors/?q=ai:susobhanan.abhimanyuSummary: Pulsar Timing Array (PTA) experiments are expected to be sensitive to gravitational waves (GWs) emitted by individual supermassive black hole binaries (SMBHBs) inspiraling along eccentric orbits. We compare the computational cost of different methods of computing the PTA signals induced by relativistic eccentric SMBHBs, namely approximate analytic expressions, Fourier series expansion, post-circular expansion, and numerical integration. We show that the fastest method for evaluating PTA signals is by using the approximate analytic expressions, which provides up to \(\sim 50\) times improvement in computational speed over the alternative methods. We investigate the accuracy of the approximate analytic expressions by employing a mismatch metric valid for PTA signals. We show that this method is accurate within the region of the binary parameter space that is of interest to PTA experiments. We introduce a spline-based method to further accelerate the PTA signal evaluations for narrowband PTA datasets. The efficient methods for computing the eccentric SMBHB-induced PTA signals were implemented in the GWecc.jl package and can be readily accessed from the popular ENTERPRISE package to search for such signals in PTA datasets. Further, we simplify the eccentric SMBHB PTA signal expression for the case of a single-pulsar search and demonstrate our computationally efficient methods by performing a single-pulsar search in the 12.5 year NANOGrav narrowband dataset of PSR J1909-3744 using the simplified expression. These results will be crucial for searching for eccentric SMBHBs in large PTA datasets.Adiabatic regularization of power spectrum and stress tensor of relic gravitational wave without low-frequency distortionhttps://zbmath.org/1527.830312024-02-28T19:32:02.718555Z"Zhang, Yang"https://zbmath.org/authors/?q=ai:zhang.yang.4"Wang, Bo"https://zbmath.org/authors/?q=ai:wang.bo.21|wang.bo.1|wang.boSummary: Adiabatic regularization is a method to remove UV divergences in quantum fields in curved spacetime. For relic gravitational wave generated during inflation, regularization on all \(k\)-modes of the power spectrum to 2nd adiabatic order, and of the energy density and pressure to 4th order, respectively, causes low-frequency distortions. To avoid these, we regularize only the short modes inside the horizon during inflation (corresponding to the present frequencies \(f \gtrsim 10^9\) Hz), and keep the long modes intact. Doing this does not violate the energy conservation since the \(k\)-modes of RGW are independent of each other during inflation. The resulting spectra are UV convergent and simultaneously free of low-frequency distortion, and these properties remain in the present spectra after evolution, in contrast to regularization at the present time which has some distortion or irregularities. The spectra generally exhibit quick oscillations in frequency domain, even if the initial spectra during inflation have no oscillations. This pattern is due to the interference between the positive and negative frequency modes developed during cosmic expansion, and may be probed by future RGW detections.\(f(R,\Sigma,T)\) gravityhttps://zbmath.org/1527.830322024-02-28T19:32:02.718555Z"Bakry, M. A."https://zbmath.org/authors/?q=ai:bakry.m-a"Ibraheem, Shymaa K."https://zbmath.org/authors/?q=ai:ibraheem.shymaa-kSummary: We used the absolute parallelism geometry to obtain a new formula for the Ricci scalar. We consider \(f(R,\Sigma,T)\) modified theories of gravity, where the gravitational Lagrangian is given by three arbitrary functions of the Ricci scalar \(R\), Ricci torsion scalar \(\Sigma\), and the trace of the stress-energy tensor \(T\). We obtain the gravitational field equations in the metric formalism. The evolution of the function \(f(R)\) withr time is studied, and we discuss the parameters that make up the function and impose constraints on these parameters. The solution of the \(f(R,\Sigma,T)\) gravity equations are obtained under a varying polynomial deceleration parameter. The effect of torsion on cosmological models is also discussed. Physical aspects of the energy density, pressure, and energy conditions of the cosmological models proposed in this article are studied, and the evolution of the physical parameters is shown in figures. Evolution of the fluid pressure and energy density parameter as a function of redshift has been obtained. The \(f(R)\) gravity and \(f(R,T)\) gravity theories as special cases could be inferred from \(f(R,\Sigma,T)\) gravity. Several special cases have been studied, with illustrations for each case.The classical and quantum implications of the Raychaudhuri equation in \(f(T)\)-gravityhttps://zbmath.org/1527.830332024-02-28T19:32:02.718555Z"Chakraborty, Madhukrishna"https://zbmath.org/authors/?q=ai:chakraborty.madhukrishna"Chakraborty, Subenoy"https://zbmath.org/authors/?q=ai:chakraborty.subenoySummary: The present work deals with the classical and quantum aspects of the Raychaudhuri equation (RE) in the framework of \(f(T)\)-gravity theory. In the background of homogeneous and isotropic Friedmann-Lemaître-Robertson-Walker space-time, the RE has been formulated and used to examine the focusing theorem and convergence condition for different choices of \(f(T)\). Finally in quantum cosmology, the wave function of the Universe has been shown to be the energy eigen function of the time-independent Schrödinger equation of a particle. Also probability measure on the minisuperspace has been examined at zero volume for singularity analysis in the quantum regime. Lastly, the Bohmian trajectory for the present quantum system has been explicitly determined for some particular choices.\(T\)-dual solutions and infinitesimal moduli of the \(G_2\)-Strominger systemhttps://zbmath.org/1527.830342024-02-28T19:32:02.718555Z"Clarke, Andrew"https://zbmath.org/authors/?q=ai:clarke.andrew.1"Garcia-Fernandez, Mario"https://zbmath.org/authors/?q=ai:garcia-fernandez.mario"Tipler, Carl"https://zbmath.org/authors/?q=ai:tipler.carlSummary: We consider \(G_2\)-structures with torsion coupled with \(G_2\)-instantons, on a compact 7-dimensional manifold. The coupling is via an equation for 4-forms which appears in supergravity and generalized geometry, known as \textit{the Bianchi identity}. First studied by Friedrich and Ivanov, the resulting system of partial differential equations describes compactifications of the heterotic string to three dimensions, and is often referred to as the \(G_2\)-\textit{Strominger system}. We study the moduli space of solutions and prove that the space of infinitesimal deformations, modulo automorphisms, is finite dimensional. We also provide a new family of solutions to this system, on \(T^3\)-bundles over \(K3\) surfaces and for infinitely many different instanton bundles, adapting a construction of Fu-Yau and the second named author. In particular, we exhibit the first examples of \(T\)-dual solutions for this system of equations.Exact geometries from boundary gravityhttps://zbmath.org/1527.830352024-02-28T19:32:02.718555Z"Gupta, Rohit K."https://zbmath.org/authors/?q=ai:gupta.rohit-k"Kar, Supriya"https://zbmath.org/authors/?q=ai:kar.supriya-k"Nitish, R."https://zbmath.org/authors/?q=ai:nitish.r"Verma, Monika"https://zbmath.org/authors/?q=ai:verma.monikaSummary: We show that the extremal Reissner-Nordström type multi-black holes in an emergent scenario are exact in General Relativity. It is shown that an axion in the bulk together with a geometric torsion ensures the required energy momentum to source the \((3 + 1)\) geometry in the Einstein tensor. Analysis reveals a significant role of dark energy in curved space-time.Static Weyssenhoff fluid sphere models in Einstein-Cartan theory of gravitationhttps://zbmath.org/1527.830362024-02-28T19:32:02.718555Z"Katkar, L. N."https://zbmath.org/authors/?q=ai:katkar.l-n"Phadatare, D. R."https://zbmath.org/authors/?q=ai:phadatare.d-rSummary: Three physically reasonable static Weyssenhoff fluid sphere models have been obtained by solving the relevant field equations of the Einstein-Cartan theory of gravitation, when Weyssenhoff fluid is the source of spin and gravitation. The spin of the gravitating matter influences the fields of these fluid sphere models. The gravitational field of two of the models is proved to be of Petrov type \(D\), while the interpretation of the gravitational field of the remaining model fails due to the influence of the spin component \(s_0\). One of the fluid sphere models is accelerating and rotating, while the other two are only rotating. Gravity in each of these models repels and prevents the collapse.Varying without varying: reparameterizations, diffeomorphisms, general covariance, Lie derivatives, and all thathttps://zbmath.org/1527.830372024-02-28T19:32:02.718555Z"Kothawala, Dawood"https://zbmath.org/authors/?q=ai:kothawala.dawood-a(no abstract)Pointwise decay for the wave equation on nonstationary spacetimeshttps://zbmath.org/1527.830382024-02-28T19:32:02.718555Z"Looi, Shi-Zhuo"https://zbmath.org/authors/?q=ai:looi.shi-zhuoSummary: This first article in a two-part series (the second article being [the author, ``Pointwise decay for the energy-critical nonlinear wave equation'', Preprint, \url{arXiv:2205.13197}]) assumes a weak form of the integrated local energy decay estimate and proves that solutions to the linear wave equation with variable coefficients in \(\mathbb{R}^{1+3}\), first-order terms, and a potential decay at a rate depending on how rapidly the vector fields of these functions decay at spatial infinity. Roughly speaking, given metric perturbation terms and first-order terms whose vector fields decay at least as rapidly as the rate \(r^{-1-a}\), and potentials whose vector fields decay at least as rapidly as the rate \(r^{-2-a}\), our results imply that \(|Z^J\phi(t,x)|\leq Ct^{-2-a}\) for bounded \(|x|\), where \(Z\) denotes vector fields and \(J\) is a multi-index. We expect that this is a sharp decay rate. We prove results for both stationary and nonstationary metrics and coefficients. The proof uses integrated local energy decay to achieve an initial decay rate, and then uses an iteration involving the one-dimensional reduction (due to the positivity of the fundamental solution of the wave equation in three spatial dimensions) to achieve the full decay rate. For second-order perturbations of the Minkowski metric with coefficients that are not necessarily spherically symmetric, we analyze these coefficients' decay rates in a novel way to obtain a higher rate of pointwise decay for the solution than might be expected, assuming only weak pointwise decay on up to two time derivatives of the coefficients (and vector fields thereof); the latter weak decay is satisfied if, for example, the metric is stationary.The geodesic flow of the BGPP metric is Liouville integrablehttps://zbmath.org/1527.830392024-02-28T19:32:02.718555Z"Maciejewski, Andrzej J."https://zbmath.org/authors/?q=ai:maciejewski.andrzej-j"Przybylska, Maria"https://zbmath.org/authors/?q=ai:przybylska.maria"Valent, Galliano"https://zbmath.org/authors/?q=ai:valent.gallianoSummary: We prove that the geodesics equations corresponding to the BGPP metric are integrable in the Liouville sense. The \(\mathrm{SO}(3, \mathbb{R})\) symmetry of the model allows to reduce the system from four to two degrees of freedom. Moreover, solutions of the reduced system and its degenerations can be given explicitly or reduced to a certain quadrature. In degenerated cases BGPP metric coincides with the Eguchi-Hanson metric and for this case the mentioned quadrature can be calculated explicitly in terms of elliptic integrals.Triple interference, non-linear Talbot effect and gravitization of the quantumhttps://zbmath.org/1527.830402024-02-28T19:32:02.718555Z"Berglund, Per"https://zbmath.org/authors/?q=ai:berglund.per"Geraci, Andrew"https://zbmath.org/authors/?q=ai:geraci.andrew"Hübsch, Tristan"https://zbmath.org/authors/?q=ai:hubsch.tristan"Mattingly, David"https://zbmath.org/authors/?q=ai:mattingly.david-m"Minic, Djordje"https://zbmath.org/authors/?q=ai:minic.djordjeSummary: Recently we have discussed a new approach to the problem of quantum gravity in which the quantum mechanical structures that are traditionally fixed, such as the Fubini-Study metric in the Hilbert space of states, become dynamical and so implement the idea of gravitizing the quantum. In this paper we elaborate on a specific test of this new approach to quantum gravity using triple interference in a varying gravitational field. Our discussion is driven by a profound analogy with recent triple-path interference experiments performed in the context of non-linear optics. We emphasize that the triple interference experiment in a varying gravitational field would deeply influence the present understanding of the kinematics of quantum gravity and quantum gravity phenomenology. We also discuss the non-linear Talbot effect as another striking phenomenological probe of gravitization of the geometry of quantum theory.Identifying universality in warm inflationhttps://zbmath.org/1527.830412024-02-28T19:32:02.718555Z"Berera, Arjun"https://zbmath.org/authors/?q=ai:berera.arjun"Mabillard, Joel"https://zbmath.org/authors/?q=ai:mabillard.joel.1"Pieroni, Mauro"https://zbmath.org/authors/?q=ai:pieroni.mauro"Ramos, Rudnei O."https://zbmath.org/authors/?q=ai:ramos.rudnei-o.1Summary: Ideas borrowed from renormalization group are applied to warm inflation to characterize the inflationary epoch in terms of flows away from the de Sitter regime. In this framework different models of inflation fall into universality classes. Furthermore, for warm inflation this approach also helps to characterise when inflation can smoothly end into the radiation dominated regime. Warm inflation has a second functional dependence compared to cold inflation due to dissipation, yet despite this feature, it is shown that the universality classes defined for cold inflation can be consistently extended to warm inflation.Cosmological hydrodynamics with relativistic pressure and velocityhttps://zbmath.org/1527.830422024-02-28T19:32:02.718555Z"Noh, Hyerim"https://zbmath.org/authors/?q=ai:noh.hyerim"Hwang, Jai-chan"https://zbmath.org/authors/?q=ai:hwang.jai-chan"Park, Chan-Gyung"https://zbmath.org/authors/?q=ai:park.chan-gyungSummary: We present hydrodynamic equations with relativistic pressure and velocity in the presence of weak gravity, in a cosmological context. Previously we consistently derived special relativistic hydrodynamic equations with weak gravity in Minkowski background. With the relativistic pressure and velocity one cannot derive the cosmological counterpart by a simple transformation from equations in the Minkowski background. Here we present a proper derivation. We point out the potential importance of relativistic pressure and velocity in gravitational lensing.A generic instability in clustering dark energy?https://zbmath.org/1527.830432024-02-28T19:32:02.718555Z"Hassani, Farbod"https://zbmath.org/authors/?q=ai:hassani.farbod"Adamek, Julian"https://zbmath.org/authors/?q=ai:adamek.julian"Kunz, Martin"https://zbmath.org/authors/?q=ai:kunz.martin"Shi, Pan"https://zbmath.org/authors/?q=ai:shi.pan"Wittwer, Peter"https://zbmath.org/authors/?q=ai:wittwer.peterSummary: In this paper, we study the effective field theory (EFT) of dark energy (DE) for the \(k\)-essence model beyond linear order. Using particle-mesh \(N\)-body simulations that consistently solve the DE evolution on a grid, we find that the next-to-leading order in the EFT expansion, which comprises the terms of the equations of motion that are quadratic in the field variables, gives rise to a generic instability in the regime of low speed of sound (high Mach number). We rule out the possibility of a numerical artefact by considering simplified cases in spherically and plane symmetric situations analytically. If the speed of sound vanishes exactly, the non-linear instability makes the evolution singular in finite time, signalling a breakdown of the EFT framework. The case of finite (but small) speed of sound is subtle, and the local singularity could be replaced by some other type of behaviour with strong non-linearities. While an ultraviolet completion may cure the problem in principle, there is no reason why this should be the case in general. As a result, for a large range of the effective speed of sound \(c_s\), a linear treatment is not adequate.Dark beam excitations in the defocusing \((2+1)\)-dimensional Zakharov systemhttps://zbmath.org/1527.830442024-02-28T19:32:02.718555Z"Zhong, Wei-Ping"https://zbmath.org/authors/?q=ai:zhong.weiping"Yang, Zhengping"https://zbmath.org/authors/?q=ai:yang.zhengping"Belić, Milivoj"https://zbmath.org/authors/?q=ai:belic.milivoj-rSummary: The defocusing \((2+1)\)-dimensional Zakharov system describes beams that involve three independent variables: the propagation distance and two orthogonal coordinates. Consequently, it can be inferred from the system characteristics that such beams exhibit considerably richer nonlinear behavior than the \((1+1)\)-dimensional systems. In this paper, using the Hirota bilinear method, we found analytical dark beam solutions of the defocusing \((2+1)\)-dimensional Zakharov system, describing beams in normal regions of nonlinear media. Based on the parameters describing dark beam solutions, some characteristics are discussed, and the impact of these parameters on the propagation of such beams is analyzed. Our results indicate that the shape of dark beams can be completely controlled by adjusting these physical parameters. In addition to finding order-1 dark beams, we also obtain the analytical order-2 dark beam solutions and the order-n dark beam solutions of the system mentioned above, and discuss those in special cases. Interestingly, it turned out that such solutions can be simplified to breathers and rogue waves. An interesting special case is that of the dark Peregrine soliton, which can be considered as the basic dark rogue wave. The basic idea of nonlinear wave control that was used in this paper can be extended to other higher-dimensional nonlinear systems.On the photon motion near a five-dimensional Schwarzschild black holehttps://zbmath.org/1527.830452024-02-28T19:32:02.718555Z"Alatas, Husin"https://zbmath.org/authors/?q=ai:alatas.husin"Nuraeni, Siti A."https://zbmath.org/authors/?q=ai:nuraeni.siti-a"Saptiani, Ilma L."https://zbmath.org/authors/?q=ai:saptiani.ilma-l"Gunara, Bobby E."https://zbmath.org/authors/?q=ai:gunara.bobby-eka(no abstract)Corrigendum to: ``Numerical solutions for the \(f(R)\)-Klein-Gordon system''https://zbmath.org/1527.830462024-02-28T19:32:02.718555Z"Beckering Vinckers, Ulrich K."https://zbmath.org/authors/?q=ai:vinckers.ulrich-k-beckering"de la Cruz-Dombriz, Álvaro"https://zbmath.org/authors/?q=ai:de-la-cruz-dombriz.alvaro"Pollney, Denis"https://zbmath.org/authors/?q=ai:pollney.denisFrom the text: Here, the authors correct five typographical errors and one computational error.
Corrigendum to the authors' paper [ibid. 40, No. 17, Article ID 175009, 30 p. (2023; Zbl 1519.83066)].Primordial black holes from inflation and quantum diffusionhttps://zbmath.org/1527.830472024-02-28T19:32:02.718555Z"Biagetti, M."https://zbmath.org/authors/?q=ai:biagetti.matteo"Franciolini, G."https://zbmath.org/authors/?q=ai:franciolini.gabriele"Kehagias, A."https://zbmath.org/authors/?q=ai:kehagias.alex"Riotto, A."https://zbmath.org/authors/?q=ai:riotto.aSummary: Primordial black holes as dark matter may be generated in single-field models of inflation thanks to the enhancement at small scales of the comoving curvature perturbation. This mechanism requires leaving the slow-roll phase to enter a non-attractor phase during which the inflaton travels across a plateau and its velocity drops down exponentially. We argue that quantum diffusion has a significant impact on the primordial black hole mass fraction making the classical standard prediction not trustable.Bose-Einstein condensates in charged black-hole spacetimeshttps://zbmath.org/1527.830482024-02-28T19:32:02.718555Z"Castellanos, Elías"https://zbmath.org/authors/?q=ai:castellanos.elias"Degollado, Juan Carlos"https://zbmath.org/authors/?q=ai:degollado.juan-carlos"Lämmerzahl, Claus"https://zbmath.org/authors/?q=ai:lammerzahl.claus"Macías, Alfredo"https://zbmath.org/authors/?q=ai:macias.alfredo"Perlick, Volker"https://zbmath.org/authors/?q=ai:perlick.volkerSummary: We analyze Bose-Einstein condensates on three types of spherically symmetric and static charged black-hole spacetimes: the Reissner-Nordström spacetime, Hoffmann's Born-Infeld black-hole spacetime, and the regular Ayón-Beato-García spacetime. The Bose-Einstein condensate is modeled in terms of a massive scalar field that satisfies a Klein-Gordon equation with a self-interaction term. The scalar field is assumed to be uncharged and not self-gravitating. If the mass parameter of the scalar field is chosen sufficiently small, there are quasi-bound states of the scalar field that may be interpreted as dark matter clouds. We estimate the size and the total energy of such clouds around charged supermassive black holes and we investigate if their observable features can be used for discriminating between the different types of charged black holes.Primordial black holes and associated gravitational waves in axion monodromy inflationhttps://zbmath.org/1527.830492024-02-28T19:32:02.718555Z"Cheng, Shu-Lin"https://zbmath.org/authors/?q=ai:cheng.shu-lin.1"Lee, Wolung"https://zbmath.org/authors/?q=ai:lee.wolung"Ng, Kin-Wang"https://zbmath.org/authors/?q=ai:ng.kin-wangSummary: In the axion monodromy inflation, the inflation is driven by the axion with super-Planckian field values in a monomial potential with superimposed sinusoidal modulations. The coupling of the axion to massless gauge fields can induce copious particle production during inflation, resulting in large non-Gaussian curvature perturbation that leads to the formation of primordial black holes. In this paper, we explore the parameter space in the axion monodromy inflation model that favors the formation of primordial black holes with masses ranging from \(10^8\) grams to 20 solar masses. We also study the associated gravitational waves and their detection in pulsar timing arrays and interferometry experiments.CMB spectral distortions from black holes formed by vacuum bubbleshttps://zbmath.org/1527.830502024-02-28T19:32:02.718555Z"Deng, Heling"https://zbmath.org/authors/?q=ai:deng.heling"Vilenkin, Alexander"https://zbmath.org/authors/?q=ai:vilenkin.alexander"Yamada, Masaki"https://zbmath.org/authors/?q=ai:yamada.masakiSummary: Vacuum bubbles may nucleate and expand during the cosmic inflation. When inflation ends, the bubbles run into the ambient plasma, producing strong shocks followed by underdensity waves, which propagate outwards. The bubbles themselves eventually form black holes with a wide distribution of masses. It has been recently suggested that such black holes may account for LIGO observations and may provide seeds for supermassive black holes observed at galactic centers. They may also provide a significant part or even the whole of the dark matter. We estimate the spectral \(\mu \)-distortion of the CMB induced by expanding shocks and underdensities. The predicted distortions averaged over the sky are well below the current bounds, but localized peaks due to the largest black holes impose constraints on the model parameters.Late-time asymptotics for geometric wave equations with inverse-square potentialshttps://zbmath.org/1527.830512024-02-28T19:32:02.718555Z"Gajic, Dejan"https://zbmath.org/authors/?q=ai:gajic.dejanSummary: We introduce a new, physical-space-based method for deriving the precise leading-order late-time behaviour of solutions to geometric wave equations on asymptotically flat spacetime backgrounds and apply it to the setting of wave equations with asymptotically inverse-square potentials on Schwarzschild black holes. This provides a useful toy model setting for introducing methods that are applicable to more general linear and nonlinear geometric wave equations, such as wave equations for electromagnetically charged scalar fields, wave equations on extremal Kerr black holes and geometric wave equations in even space dimensions, where existing proofs for deriving precise late-time asymptotics might not apply. The method we introduce relies on exploiting the spatial decay properties of time integrals of solutions to derive the existence and precise genericity properties of asymptotic late-time tails and obtain sharp, uniform decay estimates in time.Statistical ensembles and logarithmic corrections to black hole entropyhttps://zbmath.org/1527.830522024-02-28T19:32:02.718555Z"Ghosh, Aritra"https://zbmath.org/authors/?q=ai:ghosh.aritraSummary: In this paper, we consider general statistical ensembles and compute logarithmic corrections to the microcanonical entropy resulting due to thermodynamic fluctuations which are controlled by the boundary conditions, i.e. due to choice of ensemble. The framework is applied to the case of non-extremal black holes to give certain logarithmic corrections to the Bekenstein-Hawking entropy. We argue that within the framework of black hole chemistry, where the cosmological constant is identified with bulk pressure, the isoenthalpic-isobaric entropy rather than microcanonical entropy carries a more natural and consistent thermodynamic interpretation as black hole entropy. Logarithmic corrections to both microcanonical and isoenthalpic-isobaric entropies of black holes are computed, and we show that the latter set of corrections in black hole chemistry are of the same form as corrections to the microcanonical entropy in theories where the cosmological constant is not interpreted as a thermodynamic pressure. Finally, we compute logarithmic corrections to entropy in the framework of holographic black hole chemistry. We emphasize upon the choice of statistical ensemble, both in the bulk and on the boundary, in order to have a consistent comparison between them. The corrections studied in this paper are distinct from those obtained from Euclidean quantum gravity.Black hole complementarity with the generalized uncertainty principle in gravity's rainbowhttps://zbmath.org/1527.830532024-02-28T19:32:02.718555Z"Gim, Yongwan"https://zbmath.org/authors/?q=ai:gim.yongwan"Um, Hwajin"https://zbmath.org/authors/?q=ai:um.hwajin"Kim, Wontae"https://zbmath.org/authors/?q=ai:kim.wontaeSummary: When gravitation is combined with quantum theory, the Heisenberg uncertainty principle could be extended to the generalized uncertainty principle accompanying a minimal length. To see how the generalized uncertainty principle works in the context of black hole complementarity, we calculate the required energy to duplicate information for the Schwarzschild black hole. It shows that the duplication of information is not allowed and black hole complementarity is still valid even assuming the generalized uncertainty principle. On the other hand, the generalized uncertainty principle with the minimal length could lead to a modification of the conventional dispersion relation in light of Gravity's Rainbow, where the minimal length is also invariant as well as the speed of light. Revisiting the gedanken experiment, we show that the no-cloning theorem for black hole complementarity can be made valid in the regime of Gravity's Rainbow on a certain combination of parameters.Corrigendum to: ``Post-Newtonian quasicircular initial orbits for numerical relativity''https://zbmath.org/1527.830542024-02-28T19:32:02.718555Z"Healy, James"https://zbmath.org/authors/?q=ai:healy.james"Lousto, Carlos O."https://zbmath.org/authors/?q=ai:lousto.carlos-o"Nakano, Hiroyuki"https://zbmath.org/authors/?q=ai:nakano.hiroyuki"Zlochower, Yosef"https://zbmath.org/authors/?q=ai:zlochower.yosefFrom the text: There was an error in the implementation of the black holes (BH) positions relative to the center of mass. This error affects only the next-to-leading spin-orbit terms in the \(x\) and \(z\)-components of the BH coordinate locations.
Corrigendum to the authors' paper [ibid. 34, No. 14, Article ID 145011, 22 p. (2017; Zbl 1373.83057)].Magnetically charged AdS black holes and Joule-Thomson expansionhttps://zbmath.org/1527.830552024-02-28T19:32:02.718555Z"Kruglov, S. I."https://zbmath.org/authors/?q=ai:kruglov.sergey-ilichSummary: The process of the Joule-Thomson adiabatic expansion within rational NED (RNED)-AdS spacetime is investigated. The isenthalpic \(P-T\) diagrams and the inversion temperature are depicted. The inversion temperature depends on the magnetic charge and RNED coupling constant of black holes. When the Joule-Thomson coefficient vanishes, a cooling-heating phase transition occurs. We consider the cosmological constant as a thermodynamic pressure, and the black hole mass is treated as chemical enthalpy.Rotating Bardeen black hole surrounded by perfect fluid dark matter as a particle acceleratorhttps://zbmath.org/1527.830562024-02-28T19:32:02.718555Z"Li, Qi-Quan"https://zbmath.org/authors/?q=ai:li.qi-quan"Zhang, Yu"https://zbmath.org/authors/?q=ai:zhang.yu.12"Li, Qian"https://zbmath.org/authors/?q=ai:li.qian.2"Sun, Qi"https://zbmath.org/authors/?q=ai:sun.qiSummary: We study the event horizon of a rotating Bardeen black hole surrounded by perfect fluid dark matter and the black hole as a particle accelerator. The black hole is represented by four parameters: mass \(M\), rotation parameter \(a\), dark matter parameter \(\alpha\) and magnetic charge \(g\). It is interesting that when we determine the values of magnetic charge \(g\) and dark matter parameters \(\alpha\) we can get a critical rotation parameter \(a_E\) and then we get a contour plane with \(\Delta = 0\) taking three parameters as coordinates. We also derive the effective potential of the particle and the center-of-mass (CM) energy of the two particles outside the black hole by using the motion equations of the particle in the equatorial plane of the black hole. We find that the CM energy depends not only on the rotation parameter \(a\), but also on the parameters \(g\) and \(\alpha \). We discuss the CM energy for two particles colliding at the black hole horizon in the extreme and non-extreme cases, respectively. It is found that the CM energy can become arbitrarily high when the angular momentum of one of the two particles is the critical angular momentum under the background of extreme black holes and there is no such result for non-extreme black holes, because the particles do not reach the black hole horizon when the angular momentum of the particles is critical angular momentum. Therefore, we prove that the rotating Bardeen black hole surrounded by perfect fluid dark matter can be used as a particle accelerator.
{{\copyright} 2023 Institute of Theoretical Physics CAS, Chinese Physical Society and IOP Publishing}Universal ratios of critical physical quantities of charged AdS black holeshttps://zbmath.org/1527.830572024-02-28T19:32:02.718555Z"Mo, Jie-Xiong"https://zbmath.org/authors/?q=ai:mo.jie-xiong"Li, Gu-Qiang"https://zbmath.org/authors/?q=ai:li.guqiang"Xu, Xiao-Bao"https://zbmath.org/authors/?q=ai:xu.xiaobaoSummary: We investigate the ratios of critical physical quantities related to the \(T\)-\(S\) criticality of charged AdS black holes. It is shown that the ratio \(\frac{T_c S_c}{Q_c}\) is universal while \(\frac{T_c r_c}{Q_c}\) is not. This finding is quite interesting considering the former observation that both the \(T\)-\(S\) graph and \(T\)-\(r_+\) graph exhibit reverse van der Waals behavior. It is also worth noting that the value of \(\frac{T_c S_c}{Q_c}\) differs from that of \(\frac{P_c v_c}{T_c}\) for \(P\)-\(V\) criticality. Moreover, we discuss ratios for the \(P\)-\(V\) criticality and \(Q\)-\(\Phi\) criticality. By introducing the dimensional analysis technique, we successfully interpret the phenomenon that the ratio \(\frac{\Phi_c Q_c}{T_c}\) is not universal and construct two universal ratios for the \(Q\)-\(\Phi\) criticality instead. It is expected that the dimensional analysis technique can be generalized to probe the universal ratios for \(Y\)-\(X\) criticality in future research.On the global Casimir effect in the Schwarzschild spacetimehttps://zbmath.org/1527.830582024-02-28T19:32:02.718555Z"Muniz, C. R."https://zbmath.org/authors/?q=ai:muniz.celio-r"Tahim, M. O."https://zbmath.org/authors/?q=ai:tahim.makarius-o"Cunha, M. S."https://zbmath.org/authors/?q=ai:cunha.m-s"Vieira, H. S."https://zbmath.org/authors/?q=ai:vieira.h-sSummary: In this paper we study the vacuum quantum fluctuations of the stationary modes of an uncharged scalar field with mass \(m\) around a Schwarzschild black hole with mass \(M\), at zero and non-zero temperatures. The procedure consists of calculating the energy eigenvalues starting from the exact solutions found for the dynamics of the scalar field, considering a frequency cutoff in which the particle is not absorbed by the black hole. From this result, we obtain the exterior contributions for the vacuum energy associated to the stationary states of the scalar field, by considering the half-summing of the levels of energy and taking into account the respective degeneracies, in order to better capture the nontrivial topology of the black hole spacetime. Then we use the Riemann's zeta function to regularize the vacuum energy thus found. Such a regularized quantity is the Casimir energy, whose analytic computation we show to yield a convergent series. The Casimir energy obtained does not take into account any boundaries artificially imposed on the system, just the nontrivial spacetime topology associated to the source and its singularity. We suggest that this latter manifests itself through the vacuum tension calculated on the event horizon. We also investigate the problem by considering the thermal corrections via Helmholtz free energy calculation, computing the Casimir internal energy, the corresponding tension on the event horizon, the Casimir entropy, and the thermal capacity of the regularized quantum vacuum, analyzing their behavior at low and high temperatures, pointing out the thermodynamic instability of the system in the considered regime, i.e. \(mM \ll 1\).Spherically symmetric charged black hole in conformal teleparallel equivalent of general relativityhttps://zbmath.org/1527.830592024-02-28T19:32:02.718555Z"Nashed, G. G. L."https://zbmath.org/authors/?q=ai:nashed.gamal-g-l"Bamba, Kazuharu"https://zbmath.org/authors/?q=ai:bamba.kazuharuSummary: We studied 4-dimensional non-charged and charged spherically symmetric spacetimes in conformal teleparallel equivalent of general relativity. For this aim, we apply the field equations of non-charged and charged to diagonal and non-diagonal vierbeins and derive their sets of non-linear differential equations. We investigate in details that the Schwarzschild, for the non-charged case, and the Reissner-Nordström, for the charged case, are the only black hole solutions for the spherically symmetric case in the frame of conformal teleparallel equivalent of general relativity theory. Our conclusion indicates that the scalar field in the conformal teleparallel equivalent of general relativity theory has no effect for the spherically symmetric manifold.Generalized uncertainty principle, black holes, and white dwarfs: a tale of two infinitieshttps://zbmath.org/1527.830602024-02-28T19:32:02.718555Z"Ong, Yen Chin"https://zbmath.org/authors/?q=ai:ong.yen-chinSummary: It is often argued that quantum gravitational correction to the Heisenberg's uncertainty principle leads to, among other things, a black hole remnant with finite temperature. However, such a generalized uncertainty principle also seemingly removes the Chandrasekhar limit, i.e., it permits white dwarfs to be arbitrarily large, which is at odds with astrophysical observations. We show that this problem can be resolved if the parameter in the generalized uncertainty principle is negative. We also discuss the Planck scale physics of such a model.Mechanisms for primordial black hole production in string theoryhttps://zbmath.org/1527.830612024-02-28T19:32:02.718555Z"Özsoy, Ogan"https://zbmath.org/authors/?q=ai:ozsoy.ogan"Parameswaran, Susha"https://zbmath.org/authors/?q=ai:parameswaran.susha-l"Tasinato, Gianmassimo"https://zbmath.org/authors/?q=ai:tasinato.gianmassimo"Zavala, Ivonne"https://zbmath.org/authors/?q=ai:zavala.ivonneSummary: We consider mechanisms for producing a significant population of primordial black holes (PBHs) within string inspired single field models of inflation. The production of PBHs requires a large amplification in the power spectrum of curvature perturbations between scales associated with CMB and PBH formation. In principle, this can be achieved by temporarily breaking the slow-roll conditions during inflation. In this work, we identify two string setups that can realise this process. In string axion models of inflation, subleading non-perturbative effects can superimpose steep cliffs and gentle plateaus onto the leading axion potential. The cliffs can momentarily violate the slow-roll conditions, and the plateaus can lead to phases of ultra slow-roll inflation. We thus achieve a string motivated model which both matches the Planck observations at CMB scales and produces a population of light PBHs, which can account for an order one fraction of dark matter. In DBI models of inflation, a sharp increase in the speed of sound sourced by a steep downward step in the warp factor can drive the amplification. In this scenario, discovery of PBHs could indicate non-trivial dynamics in the bulk, such as flux-antibrane annihilation at the tip of a warped throat.Bardeen regular black hole with an electric sourcehttps://zbmath.org/1527.830622024-02-28T19:32:02.718555Z"Rodrigues, Manuel E."https://zbmath.org/authors/?q=ai:rodrigues.manuel-e.1"de S. Silva, Marcos V."https://zbmath.org/authors/?q=ai:de-s-silva.marcos-vSummary: If some energy conditions on the stress-energy tensor are violated, is possible construct regular black holes in General Relativity and in alternative theories of gravity. This type of solution has horizons but does not present singularities. The first regular black hole was presented by Bardeen and can be obtained from Einstein equations in the presence of an electromagnetic field. E. Ayon-Beato and A. Garcia reinterpreted the Bardeen metric as a magnetic solution of General Relativity coupled to a nonlinear electrodynamics. In this work, we show that the Bardeen model may also be interpreted as a solution of Einstein equations in the presence of an electric source, whose electric field does not behave as a Coulomb field. We analyzed the asymptotic forms of the Lagrangian for the electric case and also analyzed the energy conditions.Using dominant and weak energy conditions for build new class of regular black holeshttps://zbmath.org/1527.830632024-02-28T19:32:02.718555Z"Rodrigues, Manuel E."https://zbmath.org/authors/?q=ai:rodrigues.manuel-e"Junior, Ednaldo L. B."https://zbmath.org/authors/?q=ai:junior.ednaldo-l-b-jun"Silva, Marcos V. de S."https://zbmath.org/authors/?q=ai:de-s-silva.marcos-vSummary: We study the generalization of the mass function of classes of regular spherically symmetric black holes solutions of in 4D coming from the coupling of General Relativity with Non-linear Electrodynamics, through the requirement of the energy conditions. Imposing that the solution must be regular and that the Weak and Dominant Energy Conditions are simultaneously satisfied, for models with the symmetry \(T^0{}_0 = T^1{}_1\) of the tensor energy-momentum, we construct a new general class of regular black holes of which two cases are asymptotically Reissner-Nordstrom.Surface tension of the black hole horizonhttps://zbmath.org/1527.830642024-02-28T19:32:02.718555Z"Shu, Liangsuo"https://zbmath.org/authors/?q=ai:shu.liangsuo"Cui, Kaifeng"https://zbmath.org/authors/?q=ai:cui.kaifeng"Liu, Xiaokang"https://zbmath.org/authors/?q=ai:liu.xiaokang"Liu, Zhichun"https://zbmath.org/authors/?q=ai:liu.zhichun"Liu, Wei"https://zbmath.org/authors/?q=ai:liu.wei.28Summary: The idea of treating the horizon of a black hole as a stretched membrane with surface tension has a long history. In this work, we discuss the microscopic origin of the surface tension of the horizon in quantum pictures of spaces, which are Bose-Einstein condensates of gravitons. The horizon is a phase interface of gravitons, the surface tension of which is found to be a result of the difference in the strength of the interaction between the gravitons on its two sides. The gravitational source, such as a Schwarzschild black hole, creates a transitional zone by changing the energy and distribution of its surrounding gravitons. Archimedes' principle for gravity can be expressed as follows: ``the gravity on an object is equal to the weight of the gravitons that it displaces.''
{\copyright} 2019 WILEY-VCH Verlag GmbH \& Co. KGaA, WeinheimThe black hole event horizon as a limited two-way membranehttps://zbmath.org/1527.830652024-02-28T19:32:02.718555Z"Wolk, Brian Jonathan"https://zbmath.org/authors/?q=ai:wolk.brian-jonathanSummary: It is shown that under a set of straightforward propositions there exists, at the event horizon and at nonzero radii inside the event horizon of a nonrotating, uncharged, spherically symmetric black hole (BH), under reasonable curvature constraints, a nonempty set of virtual exchange particle modes which can propagate to the black hole's exterior. This finding reveals that a BH event horizon is not a one-way membrane, but instead a limited two-way membrane. The paper's technology also permits presentation of what is called virtual cosmic censorship, which requires that the aforesaid virtual exchange particle mode propagation tend to zero at the singularity limit.The Bañados-Silk-West effect with immovable particles near static black holes and its rotational counterparthttps://zbmath.org/1527.830662024-02-28T19:32:02.718555Z"Zaslavskii, O. B."https://zbmath.org/authors/?q=ai:zaslavskii.oleg-bSummary: The BSW effect implies that the energy \(E_{\mathrm{c.m.}}\) in the center of mass frame of two particles colliding near a black hole can become unbounded. Usually, it is assumed that the particles move along geodesics or electrogeodesics. Instead, we consider another version of this effect. One particle is situated at rest near a static, generally speaking, distorted black hole. If another particle (say, coming from infinity) collides with it, the collision energy \(E_{\mathrm{c.m.}}\) in the center of mass frame grows unboundedly (the BSW effect). The force required to keep such a particle near a black hole diverges for nonextremal horizons but remains finite and nonzero for an extremal one and vanishes in the horizon limit for ultraextremal black holes. A generalization to the rotating case implies that a particle corotates with the black hole but does not have a radial velocity. At that, the energy \(E\to 0\), provided the angular momentum \(L\) is zero. This condition replaces that of fine tuning of the parameters in the standard version of the BSW effect.Space-time slicing in Horndeski theories and its implications for non-singular bouncing solutionshttps://zbmath.org/1527.830672024-02-28T19:32:02.718555Z"Ijjas, Anna"https://zbmath.org/authors/?q=ai:ijjas.annaSummary: In this paper, we show how the proper choice of gauge is critical in analyzing the stability of non-singular cosmological bounce solutions based on Horndeski theories. We show that it is possible to construct non-singular cosmological bounce solutions with classically stable behavior for all modes with wavelengths above the Planck scale where: (a) the solution involves a stage of null-energy condition violation during which gravity is described by a modification of Einstein's general relativity; and (b) the solution reduces to Einstein gravity both before and after the null-energy condition violating stage. Similar considerations apply to galilean genesis scenarios.The regularity transformation equations: an elliptic mechanism for smoothing gravitational metrics in general relativityhttps://zbmath.org/1527.830682024-02-28T19:32:02.718555Z"Reintjes, Moritz"https://zbmath.org/authors/?q=ai:reintjes.moritz"Temple, Blake"https://zbmath.org/authors/?q=ai:temple.blakeSummary: A central question in General Relativity (GR) is how to determine whether singularities are geometrical properties of spacetime, or simply anomalies of a coordinate system used to parameterize the spacetime. In particular, it is an open problem whether there always exist coordinate transformations which smooth a gravitational metric to optimal regularity, two full derivatives above the curvature tensor, or whether \textit{regularity singularities} exist. We resolve this open problem above a threshold level of smoothness by proving in this paper that the existence of such coordinate transformations is equivalent to solving a system of nonlinear elliptic equations in the unknown Jacobian and transformed connection, both viewed as matrix valued differential forms. We name these the \textit{Regularity Transformation equations}, or \textit{RT-equations}. In a companion paper we prove existence of solutions to the RT-equations for connections \(\Gamma \in W^{m,p}\), curvature \(\mathrm{Riem}(\Gamma) \in W^{m,p}\), assuming \(m \geq 1\), \(p > n\). Taken together, these results imply that there always exist coordinate transformations which smooth arbitrary connections to optimal regularity, (one derivative more regular than the curvature), and there are no regularity singularities, above the threshold \(m \geq 1\), \(p > n\). Authors are currently working on extending these methods to the case of GR shock waves, when gravitational metrics are only Lipschitz continuous, (\(m = 0\), \(p = \infty)\), and optimal regularity is required to recover basic properties of spacetime.Singularities in spherically symmetric solutions with limited curvature invariantshttps://zbmath.org/1527.830692024-02-28T19:32:02.718555Z"Yoshida, Daisuke"https://zbmath.org/authors/?q=ai:yoshida.daisuke"Brandenberger, Robert H."https://zbmath.org/authors/?q=ai:brandenberger.robert-hSummary: We investigate static, spherically symmetric solutions in gravitational theories which have limited curvature invariants, aiming to remove the singularity in the Schwarzschild space-time. We find that if we only limit the Gauss-Bonnet term and the Ricci scalar, then the singularity at the origin persists. Moreover we find that the position corresponding to the event horizon in the original Schwarzschild space-time can develop a curvature singularity, which we call thunderbolt singularity. We also investigate a new class of theories in which all components of the Riemann tensor are bounded. We find that the thunderbolt singularity is avoidable in this theory. However, other kinds of singularities due to the dynamics of additional degrees of freedom cannot be removed, and the space-time remains singular.Lower-dimensional Regge-Teitelboim gravityhttps://zbmath.org/1527.830702024-02-28T19:32:02.718555Z"Sheykin, Anton"https://zbmath.org/authors/?q=ai:sheykin.anton-a"Grechko, Agata"https://zbmath.org/authors/?q=ai:grechko.agataSummary: We study modified gravity theory known as the Regge-Teitelboim approach, in which gravity is represented by the dynamics of a surface isometrically embedded in a flat bulk. We obtain some particular solutions of Regge-Teitelboim equations corresponding to a circularly symmetric vacuum \(2+1\)-dimensional space-time. In contrast to GR, this vacuum space-time is not flat, so it is possible for the gravitational field to exist even without matter or a cosmological constant.JT gravity and the ensembles of random matrix theoryhttps://zbmath.org/1527.830712024-02-28T19:32:02.718555Z"Stanford, Douglas"https://zbmath.org/authors/?q=ai:stanford.douglas"Witten, Edward"https://zbmath.org/authors/?q=ai:witten.edwardSummary: We generalize the recently discovered relationship between JT gravity and double-scaled random matrix theory to the case that the boundary theory may have time-reversal symmetry and may have fermions with or without supersymmetry. The matching between variants of JT gravity and matrix ensembles depends on the assumed symmetries. Time-reversal symmetry in the boundary theory means that unorientable spacetimes must be considered in the bulk. In such a case, the partition function of JT gravity is still related to the volume of the moduli space of conformal structures, but this volume has a quantum correction and has to be computed using Reidemeister-Ray-Singer ``torsion.'' Presence of fermions in the boundary theory (and thus a symmetry \((-1)^\mathsf{F}\)) means that the bulk has a spin or pin structure. Supersymmetry in the boundary means that the bulk theory is associated to JT supergravity and is related to the volume of the moduli space of super Riemann surfaces rather than of ordinary Riemann surfaces. In all cases we match JT gravity or supergravity with an appropriate random matrix ensemble. All ten standard random matrix ensembles make an appearance -- the three Dyson ensembles and the seven Altland-Zirnbauer ensembles. To facilitate the analysis, we extend to the other ensembles techniques that are most familiar in the case of the original Wigner-Dyson ensemble of hermitian matrices. We also generalize Mirzakhani's recursion for the volumes of ordinary moduli space to the case of super Riemann surfaces.Anisotropic massive gauge-flationhttps://zbmath.org/1527.830722024-02-28T19:32:02.718555Z"Adshead, Peter"https://zbmath.org/authors/?q=ai:adshead.peter"Liu, Aike"https://zbmath.org/authors/?q=ai:liu.aikeSummary: We study anisotropic inflationary solutions in massive Gauge-flation. We work with the theory in both the Stueckelberg and dynamical symmetry-breaking limits and demonstrate that extended periods of accelerated anisotropic expansion are possible. In the case of dynamical symmetry breaking, we show that spacetime can transition from isotropic quasi-de Sitter space to an accelerating Bianchi spacetime due to a rolling Higgs field -- the spacetime can develop hair. Similarly, symmetry restoring transitions are possible from accelerating Bianchi spacetime to quasi-de Sitter space -- the spacetime can lose its hair. These transitions can be arranged to occur quickly, within an \textit{e}-folding or so, or over tens of \textit{e}-folds.Doppelgänger dark energy: modified gravity with non-universal couplings after GW170817https://zbmath.org/1527.830732024-02-28T19:32:02.718555Z"Amendola, Luca"https://zbmath.org/authors/?q=ai:amendola.luca"Bettoni, Dario"https://zbmath.org/authors/?q=ai:bettoni.dario"Domènech, Guillem"https://zbmath.org/authors/?q=ai:domenech.guillem"Gomes, Adalto R."https://zbmath.org/authors/?q=ai:gomes.adalto-rSummary: Gravitational Wave (GW) astronomy severely narrowed down the theoretical space for scalar-tensor theories. We propose a new class of attractor models {for Horndeski action} in which GWs propagate at the speed of light in the nearby universe but not in the past. To do so we derive new solutions to the interacting dark sector in which the ratio of dark energy and dark matter remains constant, which we refer to as \textit{doppelgänger dark energy} (DDE). We then remove the interaction between dark matter and dark energy by a suitable change of variables. The accelerated expansion that (we) baryons observe is due to a conformal coupling to the dark energy scalar field. We show how in this context it is possible to find a non trivial subset of solutions in which GWs propagate at the speed of light only at low red-shifts. The model is an attractor, thus reaching the limit \(c_T\to1\) relatively fast. However, the effect of baryons turns out to be non-negligible and severely constrains the form of the Lagrangian. In passing, we found that in the simplest DDE models the no-ghost conditions for perturbations require a non-universal coupling to gravity. In the end, we comment on possible ways to solve the lack of matter domination stage for DDE models.Palatini inflation in models with an \(R^2\) termhttps://zbmath.org/1527.830742024-02-28T19:32:02.718555Z"Antoniadis, I."https://zbmath.org/authors/?q=ai:antoniadis.ignatios"Karam, A."https://zbmath.org/authors/?q=ai:karam.alexandros"Lykkas, A."https://zbmath.org/authors/?q=ai:lykkas.angelos"Tamvakis, K."https://zbmath.org/authors/?q=ai:tamvakis.kyriakosSummary: The Starobinsky model, considered in the framework of the Palatini formalism, in contrast to the metric formulation, does not provide us with a model for inflation, due to the absence of a propagating scalar degree of freedom that can play the role of the inflaton. In the present article we study the Palatini formulation of the Starobinsky model coupled, in general nonminimally, to scalar fields and analyze its inflationary behavior. We consider scalars, minimally or nonminimally coupled to the Starobinsky model, such as a quadratic model, the induced gravity model or the standard Higgs-like inflation model and analyze the corresponding modifications favorable to inflation. In addition we examine the case of a classically scale-invariant model driven by the Coleman-Weinberg mechanism. In the slow-roll approximation, we analyze the inflationary predictions of these models and compare them to the latest constraints from the Planck collaboration. In all cases, we find that the effect of the \(R^2\) term is to lower the value of the tensor-to-scalar ratio.The well-tempered cosmological constanthttps://zbmath.org/1527.830752024-02-28T19:32:02.718555Z"Appleby, Stephen"https://zbmath.org/authors/?q=ai:appleby.stephen-a"Linder, Eric V."https://zbmath.org/authors/?q=ai:linder.eric-vSummary: Self tuning is one of the few methods for dynamically cancelling a large cosmological constant and yet giving an accelerating universe. Its drawback is that it tends to screen all sources of energy density, including matter. We develop a model that tempers the self tuning so the dynamical scalar field still cancels an arbitrary cosmological constant, including the vacuum energy through any high energy phase transitions, without affecting the matter fields. The scalar-tensor gravitational action is simple, related to cubic Horndeski gravity, with a nonlinear derivative interaction plus a tadpole term. Applying shift symmetry and using the property of degeneracy of the field equations we find families of functions that admit de Sitter solutions with expansion rates that are independent of the magnitude of the cosmological constant and preserve radiation and matter dominated phases. That is, the method can deliver a standard cosmic history including current acceleration, despite the presence of a Planck scale cosmological constant.Distortion of the standard cosmology in \(R + R^2\) theoryhttps://zbmath.org/1527.830762024-02-28T19:32:02.718555Z"Arbuzova, E. V."https://zbmath.org/authors/?q=ai:arbuzova.e-v"Dolgov, A. D."https://zbmath.org/authors/?q=ai:dolgov.alexandre-dmitrievich"Singh, R. S."https://zbmath.org/authors/?q=ai:singh.radhey-s|singh.ravi-sSummary: Universe history in \(R^2\)-gravity is studied from ``beginning'' up to the present epoch. It is assumed that initially the curvature scalar \(R\) was sufficiently large to induce the proper duration of inflation. Gravitational particle production by the oscillating \(R(t)\) led to a graceful exit from inflation, but the cosmological evolution in the early universe was drastically different from the standard one till the universe age reached the value of the order of the inverse decay rate of the oscillating curvature \(R(t)\). This deviation from the standard cosmology might have a noticeable impact on the formation of primordial black holes and baryogenesis. At later time, after exponential decay of the curvature oscillations, cosmology may return to normality.Nonlinear evolution of initially biased tracers in modified gravityhttps://zbmath.org/1527.830772024-02-28T19:32:02.718555Z"Aviles, Alejandro"https://zbmath.org/authors/?q=ai:aviles.alejandro"Rodriguez-Meza, Mario Alberto"https://zbmath.org/authors/?q=ai:rodriguez-meza.mario-alberto"De-Santiago, Josue"https://zbmath.org/authors/?q=ai:de-santiago.josue"Cervantes-Cota, Jorge L."https://zbmath.org/authors/?q=ai:cervantes-cota.jorge-lSummary: In this work we extend the perturbation theory for modified gravity (MG) in two main aspects. First, the construction of matter overdensities from Lagrangian displacement fields is shown to hold in a general framework, allowing us to find Standard Perturbation Theory (SPT) kernels from known Lagrangian Perturbation Theory (LPT) kernels. We then develop a theory of biased tracers for generalized cosmologies, extending already existing formalisms for \(\Lambda\)CDM. We present the correlation function in Convolution-LPT and the power spectrum in SPT for \(\Lambda\)CDM, \(f(R)\) Hu-Sawicky, and DGP braneworld models. Our formalism can be applied to many generalized cosmologies and to facilitate it, we are making public a code to compute these statistics. We further study the relaxation of bias with the use of a simple model and of excursion set theory, showing that in general the bias parameters have smaller values in MG than in General Relativity.Conformally-flat, non-singular static metric in infinite derivative gravityhttps://zbmath.org/1527.830782024-02-28T19:32:02.718555Z"Buoninfante, Luca"https://zbmath.org/authors/?q=ai:buoninfante.luca"Koshelev, Alexey S."https://zbmath.org/authors/?q=ai:koshelev.alexey-s"Lambiase, Gaetano"https://zbmath.org/authors/?q=ai:lambiase.gaetano"Marto, João"https://zbmath.org/authors/?q=ai:marto.joao.1"Mazumdar, Anupam"https://zbmath.org/authors/?q=ai:mazumdar.anupam.4Summary: In Einstein's theory of general relativity the vacuum solution yields a blackhole with a curvature singularity, where there exists a point-like source with a Dirac delta distribution which is introduced as a boundary condition in the static case. It has been known for a while that \textit{ghost-free} infinite derivative theory of gravity can ameliorate such a singularity at least at the level of linear perturbation around the Minkowski background. In this paper, we will show that the Schwarzschild metric does not satisfy the boundary condition at the origin within infinite derivative theory of gravity, since a Dirac delta source is smeared out by non-local gravitational interaction. We will also show that the spacetime metric becomes conformally-flat and singularity-free within the non-local region, which can be also made devoid of an event horizon. Furthermore, the scale of non-locality ought to be as large as that of the Schwarzschild radius, in such a way that the gravitational potential in any metric has to be always bounded by one, implying that gravity remains weak from the infrared all the way up to the ultraviolet regime, in concurrence with the results obtained in [arXiv:1707.00273]. The singular Schwarzschild blackhole can now be potentially replaced by a non-singular compact object, whose core is governed by the mass and the \textit{effective} scale of non-locality.Fifth forces, Higgs portals and broken scale invariancehttps://zbmath.org/1527.830792024-02-28T19:32:02.718555Z"Burrage, Clare"https://zbmath.org/authors/?q=ai:burrage.clare"Copeland, Edmund J."https://zbmath.org/authors/?q=ai:copeland.edmund-j.1"Millington, Peter"https://zbmath.org/authors/?q=ai:millington.peter.3"Spannowsky, Michael"https://zbmath.org/authors/?q=ai:spannowsky.michaelSummary: We study the relationship between the strength of fifth forces and the origin of scale breaking in the Standard Model (SM) of particle physics. We start with a light scalar field that is conformally coupled to a toy SM matter sector through a Weyl rescaling of the metric. After appropriately normalizing the fields, the conformally coupled scalar only interacts directly with the would-be Higgs field through kinetic-mixing and Higgs-portal terms. Thus, for the first time, we describe the equivalence of conformally coupled scalar-tensor modifications of gravity and Higgs-portal theories, and we find that the usual tree-level fifth forces only emerge if there is mass mixing between the conformally coupled scalar and the Higgs field. The strength of the fifth force, mediated by the light scalar, then depends on whether the mass of the Higgs arises from an explicit symmetry-breaking term or a spontaneous mechanism of scale breaking. Solar System tests of gravity and the non-observation of fifth forces therefore have the potential to provide information about the structure of the Higgs sector and the origin of its symmetry breaking, setting an upper bound on the magnitude of any explicit scale-breaking terms. These results demonstrate the phenomenological importance (both for cosmology and high-energy physics) of considering how scalar-tensor modifications of gravity are embedded within extensions of the SM.Minimally modified theories of gravity: a playground for testing the uniqueness of general relativityhttps://zbmath.org/1527.830802024-02-28T19:32:02.718555Z"Carballo-Rubio, Raúl"https://zbmath.org/authors/?q=ai:carballo-rubio.raul.3"Di Filippo, Francesco"https://zbmath.org/authors/?q=ai:di-filippo.francesco"Liberati, Stefano"https://zbmath.org/authors/?q=ai:liberati.stefanoSummary: In a recent paper [\textit{C. Lin} and \textit{S. Mukohyama}, J. Cosmol. Astropart. Phys. 2017, No. 10, Paper No. 33, 20 p. (2017; Zbl 1515.83230)], it was introduced a new class of gravitational theories with two local degrees of freedom. The existence of these theories apparently challenges the distinctive role of general relativity as the unique non-linear theory of massless spin-2 particles. Here we perform a comprehensive analysis of these theories with the aim of (i) understanding whether or not these are actually equivalent to general relativity, and (ii) finding the root of the variance in case these are not. We have found that a broad set of seemingly different theories actually pass all the possible tests of equivalence to general relativity (in vacuum) that we were able to devise, including the analysis of scattering amplitudes using on-shell techniques. These results are complemented with the observation that the only examples which are manifestly not equivalent to general relativity either do not contain gravitons in their spectrum, or are not guaranteed to include only two local degrees of freedom once radiative corrections are taken into account. Coupling to matter is also considered: we show that coupling these theories to matter in a consistent way is not as straightforward as one could expect. Minimal coupling, as well as the most straightforward non-minimal couplings, cannot be used. Therefore, before being able to address any issues in the presence of matter, it would be necessary to find a consistent (and in any case rather peculiar) coupling scheme.Erratum to: ``Minimally modified theories of gravity: a playground for testing the uniqueness of general relativity''https://zbmath.org/1527.830812024-02-28T19:32:02.718555Z"Carballo-Rubio, Raúl"https://zbmath.org/authors/?q=ai:carballo-rubio.raul"Di Filippo, Francesco"https://zbmath.org/authors/?q=ai:di-filippo.francesco"Liberati, Stefano"https://zbmath.org/authors/?q=ai:liberati.stefanoSummary: In this erratum we correct a mistake in the published version of this paper [ibid. 2018, No. 6, Paper No. 26, 34 p. (2018; Zbl 1527.83080)] that changes the leading behavior for large momenta of certain Feynman diagrams and modifies the set of \(n\)-point amplitudes that can be shown to be equivalent to the corresponding amplitudes of general relativity. The physical conclusions in the paper remain unchanged.Stealth configurations in vector-tensor theories of gravityhttps://zbmath.org/1527.830822024-02-28T19:32:02.718555Z"Chagoya, Javier"https://zbmath.org/authors/?q=ai:chagoya.javier"Tasinato, Gianmassimo"https://zbmath.org/authors/?q=ai:tasinato.gianmassimoSummary: Studying the physics of compact objects in modified theories of gravity is important for understanding how future observations can test alternatives to General Relativity. We consider a subset of vector-tensor Galileon theories of gravity characterized by new symmetries, which can prevent the propagation of the vector longitudinal polarization, even in absence of abelian gauge invariance. We investigate new spherically symmetric and slowly rotating solutions for these systems, including an arbitrary matter Lagrangian. We show that, under certain conditions, there always exist stealth configurations whose geometry coincides with solutions of Einstein gravity coupled with the additional matter. Such solutions have a non-trivial profile for the vector field, characterized by independent integration constants, which extends to asymptotic infinity. We interpret our findings in terms of the symmetries and features of the original vector-tensor action, and on the number of degrees of freedom that it propagates. These results are important to eventually describe gravitationally bound configurations in modified theories of gravity, such as black holes and neutron stars, including realistic matter fields forming or surrounding the object.Gravity's islands: parametrizing Horndeski stabilityhttps://zbmath.org/1527.830832024-02-28T19:32:02.718555Z"Denissenya, Mikhail"https://zbmath.org/authors/?q=ai:denissenya.mikhail"Linder, Eric V."https://zbmath.org/authors/?q=ai:linder.eric-vSummary: Cosmic acceleration may be due to modified gravity, with effective field theory or property functions describing the theory. Connection to cosmological observations through practical parametrization of these functions is difficult and also faces the issue that not all assumed time dependence or parts of parameter space give a stable theory. We investigate the relation between parametrization and stability in Horndeski gravity, showing that the results are highly dependent on the function parametrization. This can cause misinterpretations of cosmological observations, hiding and even ruling out key theoretical signatures. We discuss approaches and constraints that can be placed on the property functions and scalar sound speed to preserve some observational properties, but find that parametrizations closest to the observations, e.g. in terms of the gravitational strengths, offer more robust physical interpretations. In addition we present an example of how future observations of the B-mode polarization of the cosmic microwave background from primordial gravitational waves can probe different aspects of gravity.Observed galaxy power spectrum in cubic Galileon modelhttps://zbmath.org/1527.830842024-02-28T19:32:02.718555Z"Dinda, Bikash R."https://zbmath.org/authors/?q=ai:dinda.bikash-r"Hossain, Md. Wali"https://zbmath.org/authors/?q=ai:hossain.md-wali"Sen, Anjan A."https://zbmath.org/authors/?q=ai:sen.anjan-anandaSummary: In this paper, we study the effects of general relativistic corrections on the observed galaxy power spectrum in thawing class of cubic Galileon model with linear potential that preserves the shift symmetry. In this scenario, the observed galaxy power spectrum differs from the standard matter power spectrum mainly due to redshift space distortion (RSD) factor and relativistic effects. The RSD term enhances the matter power spectrum both at larger and smaller scales whereas the relativistic terms further enhance the matter power spectrum only at larger scales. In comparison with \(\Lambda\)CDM, the observed galaxy power spectrum is always suppressed at large scales in this scenario although this suppression is always small compared to the canonical quintessence scenario. We also study the small scale non linear power spectrum for Galileon model using the publicly available HMcode. Our study shows that at the nonlinear regime, the small scale power is enhanced in Galileon model compared to the \(\Lambda\)CDM. But this enhancement in Galileon model is lower than the quintessence case.Higher derivative mimetic gravityhttps://zbmath.org/1527.830852024-02-28T19:32:02.718555Z"Gorji, Mohammad Ali"https://zbmath.org/authors/?q=ai:gorji.mohammad-ali"Hosseini Mansoori, Seyed Ali"https://zbmath.org/authors/?q=ai:hosseini-mansoori.seyed-ali"Firouzjahi, Hassan"https://zbmath.org/authors/?q=ai:firouzjahi.hassanSummary: We study cosmological perturbations in mimetic gravity in the presence of classified higher derivative terms which can make the mimetic perturbations stable. We show that the quadratic higher derivative terms which are independent of curvature and the cubic higher derivative terms which come from curvature corrections are sufficient to remove instabilities in mimetic perturbations. The classified higher derivative terms have the same dimensions but they contribute differently in the background and perturbed equations. Therefore, we can control both the background and the perturbation equations allowing us to construct the higher derivative extension of mimetic dark matter and the mimetic nonsingular bouncing scenarios. The latter can be thought as a new higher derivative effective action for the loop quantum cosmology scenario in which the equations of motion coincide with those suggested by loop quantum cosmology. We investigate a possible connection between the mimetic cosmology and the Randall-Sundrum cosmology.Time dependent geometry in massive gravityhttps://zbmath.org/1527.830862024-02-28T19:32:02.718555Z"Heydarzade, Yaghoub"https://zbmath.org/authors/?q=ai:heydarzade.yaghoub.2"Rudra, Prabir"https://zbmath.org/authors/?q=ai:rudra.prabir.3"Pourhassan, Behnam"https://zbmath.org/authors/?q=ai:pourhassan.behnam"Faizal, Mir"https://zbmath.org/authors/?q=ai:faizal.mir"Ali, Ahmed Farag"https://zbmath.org/authors/?q=ai:ali.ahmed-farag"Darabi, Farhad"https://zbmath.org/authors/?q=ai:darabi.farhadSummary: In this paper, we will analyze a time dependent geometry in a massive theory of gravity. This will be done by analyzing Vaidya spacetime in such a massive theory of gravity. As gravitational collapse is a time dependent system, we will analyze it using the Vaidya spacetime in massive gravity. The Vainshtein and dRGT mechanisms are used to obtain a ghost free massive gravity, and construct such time dependent solutions. Singularities formed, their nature and strength will be studied in detail. We will also study the thermodynamical aspects of such a geometry by calculating the important thermodynamical quantities for such a system, and analyzing the thermodynamical behavior of such quantities.Tsunamis and ripples: effects of scalar waves on screening in the Milky Wayhttps://zbmath.org/1527.830872024-02-28T19:32:02.718555Z"Ip, Hiu Yan Sam"https://zbmath.org/authors/?q=ai:ip.hiu-yan-sam"Schmidt, Fabian"https://zbmath.org/authors/?q=ai:schmidt.fabianSummary: Modified gravity models which include an additional propagating degree of freedom are typically studied in the quasi-static limit, where the propagation is neglected, and the wave equation of the field is replaced with a Poisson-type equation. Recently, it has been proposed that, in the context of models with symmetron- or chameleon-type screening, scalar waves from astrophysical or cosmological events could have a significant effect on the screening of the Solar System, and hence invalidate these models. Here, we quantitatively investigate the impact of scalar waves by solving the full field equation linearised in the wave amplitude. In the symmetron case, we find that the quantitative effect of waves is generally negligible, even for the largest amplitudes of waves that are physically expected. In order to spoil the screening in the Solar System, a significant amount of wave energy would have to be focused on the Solar System by arranging the sources in a spherical shell centred on Earth. In the chameleon case, we are able to rule out any significant effects of propagating waves on Solar System tests.Modified Einstein's gravity to probe the sub- and super-Chandrasekhar limiting mass white dwarfs: a new perspective to unify under- and over-luminous type Ia supernovaehttps://zbmath.org/1527.830882024-02-28T19:32:02.718555Z"Kalita, Surajit"https://zbmath.org/authors/?q=ai:kalita.surajit"Mukhopadhyay, Banibrata"https://zbmath.org/authors/?q=ai:mukhopadhyay.banibrata.1Summary: Type Ia supernovae (SNeIa), used as one of the standard candles in astrophysics, are believed to form when the mass of the white dwarf approaches Chandrasekhar mass limit. However, observations in last few decades detected some peculiar SNeIa, which are predicted to be originating from white dwarfs of mass much less than the Chandrasekhar mass limit or much higher than it. Although the unification of these two sub-classes of SNeIa was attempted earlier by our group, in this work, we, for the first time, explain this phenomenon in terms of just one property of the white dwarf which is its central density. Thereby we do not vary the fundamental parameters of the underlying gravity model in the contrary to the earlier attempt. We effectively consider higher order corrections to the Starobinsky-\(f(R)\) gravity model to reveal the unification. We show that the limiting mass of a white dwarf is \(\sim M_\odot\) for central density \(\rho_c \sim 1.4\times 10^8\) g/cc, while it is \(\sim 2.8 M_\odot\) for \(\rho_c \sim1.6\times 10^{10}\) g/cc under the same model parameters. We further confirm that these models are viable with respect to the solar system test. This perhaps enlightens very strongly the long standing puzzle lying with the predicted variation of progenitor mass in SNeIa.Black hole perturbations in vector-tensor theories: the odd-mode analysishttps://zbmath.org/1527.830892024-02-28T19:32:02.718555Z"Kase, Ryotaro"https://zbmath.org/authors/?q=ai:kase.ryotaro"Minamitsuji, Masato"https://zbmath.org/authors/?q=ai:minamitsuji.masato"Tsujikawa, Shinji"https://zbmath.org/authors/?q=ai:tsujikawa.shinji"Zhang, Ying-li"https://zbmath.org/authors/?q=ai:zhang.yingli|zhang.ying-liSummary: In generalized Proca theories with vector-field derivative couplings, a bunch of hairy black hole solutions have been derived on a static and spherically symmetric background. In this paper, we formulate the odd-parity black hole perturbations in generalized Proca theories by expanding the corresponding action up to second order and investigate whether or not black holes with vector hair suffer ghost or Laplacian instabilities. We show that the models with cubic couplings \(G_3(X)\), where \(X =-A_\mu A^\mu/2\) with a vector field \(A_\mu\), do not provide any additional stability condition as in General Relativity. On the other hand, the exact charged stealth Schwarzschild solution with a nonvanishing longitudinal vector component \(A_1\), which originates from the coupling to the Einstein tensor \(G^{\mu\nu} A_\mu A_\nu\) equivalent to the quartic coupling \(G_4(X)\) containing a linear function of \(X\), is unstable in the vicinity of the event horizon. The same instability problem also persists for hairy black holes arising from general quartic power-law couplings \(G_4(X) \supset \beta_4 X^n\) with the nonvanishing \(A_1\), while the other branch with \(A_1 = 0\) can be consistent with conditions for the absence of ghost and Laplacian instabilities. We also discuss the case of other exact and numerical black hole solutions associated with intrinsic vector-field derivative couplings and show that there exists a wide range of parameter spaces in which the solutions suffer neither ghost nor Laplacian instabilities against odd-parity perturbations.Unification of dark matter-dark energy in generalized Galileon theorieshttps://zbmath.org/1527.830902024-02-28T19:32:02.718555Z"Koutsoumbas, George"https://zbmath.org/authors/?q=ai:koutsoumbas.george"Ntrekis, Konstantinos"https://zbmath.org/authors/?q=ai:ntrekis.konstantinos"Papantonopoulos, Eleftherios"https://zbmath.org/authors/?q=ai:papantonopoulos.eleftherios"Saridakis, Emmanuel N."https://zbmath.org/authors/?q=ai:saridakis.emmanuel-nSummary: We present a unified description of the dark matter and the dark energy sectors, in the framework of shift-symmetric generalized Galileon theories. Considering a particular combination of terms in the Horndeski Lagrangian in which we have not introduced a cosmological constant or a matter sector, we obtain an effective unified cosmic fluid whose equation of state \(w_U\) is zero during the whole matter era, namely from redshifts \(z \sim 3000\) up to \(z \sim 2\)--3. Then at smaller redshifts it starts decreasing, passing the bound \(w_U = -1/3\), which marks the onset of acceleration, at around \(z \sim 0.5\). At present times it acquires the value \(w_U = -0.7\). Finally, it tends toward a de-Sitter phase in the far future. This behaviour is in excellent agreement with observations. Additionally, confrontation with Supernovae type Ia data leads to a very efficient fit. Examining the model at the perturbative level, we show that it is free from pathologies such as ghosts and Laplacian instabilities, at both scalar and tensor sectors, at all times.Weakly charged compact stars in \(f(R)\) gravityhttps://zbmath.org/1527.830912024-02-28T19:32:02.718555Z"Mansour, H."https://zbmath.org/authors/?q=ai:mansour.h"Lakhal, B. Si"https://zbmath.org/authors/?q=ai:si-lakhal.b"Yanallah, A."https://zbmath.org/authors/?q=ai:yanallah.aSummary: We study electrically charged compact stars in the framework of one class of the extended theories of gravity (ETG), namely the \(f(R)\) gravity theory. We assume that the charge density is proportional to the energy density. The polytropic equation of state is chosen to describe the state of the charged perfect fluid. We aim to find the Oppenheimer Volkoff (OV) mass limit for charged compact stars. A detailed numerical study is performed. We show the dependence of the mass-radius diagram of the spheres on the values of the small parameter \(\beta\), the polytropic exponent \(\gamma\) and the charge fraction \(\alpha\). Our results are compared with those found in the literature in the case of applying General Relativity (GR).Higher-derivative operators and effective field theory for general scalar-tensor theorieshttps://zbmath.org/1527.830922024-02-28T19:32:02.718555Z"Solomon, Adam R."https://zbmath.org/authors/?q=ai:solomon.adam-ross"Trodden, Mark"https://zbmath.org/authors/?q=ai:trodden.markSummary: We discuss the extent to which it is necessary to include higher-derivative operators in the effective field theory of general scalar-tensor theories. We explore the circumstances under which it is correct to restrict to second-order operators only, and demonstrate this using several different techniques, such as reduction of order and explicit field redefinitions. These methods are applied, in particular, to the much-studied Horndeski theories. The goal is to clarify the application of effective field theory techniques in the context of popular cosmological models, and to explicitly demonstrate how and when higher-derivative operators can be cast into lower-derivative forms suitable for numerical solution techniques.A de Sitter tachyonic braneworld revisitedhttps://zbmath.org/1527.830932024-02-28T19:32:02.718555Z"Barbosa-Cendejas, Nandinii"https://zbmath.org/authors/?q=ai:barbosa-cendejas.nandinii"Cartas-Fuentevilla, Roberto"https://zbmath.org/authors/?q=ai:cartas-fuentevilla.roberto"Herrera-Aguilar, Alfredo"https://zbmath.org/authors/?q=ai:herrera-aguilar.alfredo"Mora-Luna, Refugio Rigel"https://zbmath.org/authors/?q=ai:mora-luna.refugio-rigel"Rocha, Roldão da"https://zbmath.org/authors/?q=ai:rocha.roldao-daSummary: Within the framework of braneworlds, several interesting physical effects can be described in a wide range of energy scales, starting from high-energy physics to cosmology and low-energy physics. An usual way to generate a thick braneworld model relies in coupling a bulk scalar field to higher dimensional warped gravity. Quite recently, a novel braneworld was generated with the aid of a tachyonic bulk scalar field, having several remarkable properties. It comprises a regular and stable solution that contains a relevant 3-brane with de Sitter induced metric, arising as an exact solution to the 5D field equations, describing the inflationary eras of our Universe. Besides, it is \textit{asymptotically flat}, despite of the presence of a negative 5D cosmological constant, which is an interesting feature that contrasts with most of the known, asymptotically either dS or AdS models. Moreover, it encompasses a graviton spectrum with a single massless bound state, accounting for 4D gravity localized on the brane, separated from the continuum of Kaluza-Klein massive graviton modes by a mass gap that makes the 5D corrections to Newton's law to decay exponentially. Finally, gauge, scalar and fermion fields are also shown to be localized on this braneworld. In this work, we show that this tachyonic braneworld allows for a nontrivial solution with a vanishing 5D cosmological constant that preserves all the above mentioned remarkable properties with a less amount of parameters, constituting an important contribution to the construction of a realistic cosmological braneworld model.Open problems on classical de Sitter solutionshttps://zbmath.org/1527.830942024-02-28T19:32:02.718555Z"Andriot, David"https://zbmath.org/authors/?q=ai:andriot.davidSummary: Classical 10d string backgrounds with a 4d de Sitter space-time, \(D\)-brane and orientifold sources, are commonly believed to satisfy the following:
\begin{itemize}
\item[1.] \textit{There is no classical de Sitter solution with parallel sources}.
\item[2.] \textit{Classical de Sitter solutions with intersecting sources are unstable}.
\item[3.] \textit{Classical de Sitter solutions cannot have at the same time a large internal volume, a small string coupling, a bounded number of orientifolds and quantized fluxes}.
\end{itemize}
These three conjectures are of particular relevance to the swampland program, and if true, they challenge the connection of string theory to cosmology. We restrict here to a standard solution ansatz for which the problem is well-defined, and we still fail to prove analytically any of these conjectures. While developing new tools and obtaining new constraints, we identify remaining corners of parameter space where counter-examples to these conjectures could be found.
{\copyright} 2019 WILEY-VCH Verlag GmbH \& Co. KGaA, WeinheimSmall-field and scale-free: inflation and ekpyrosis at their extremeshttps://zbmath.org/1527.830952024-02-28T19:32:02.718555Z"Lehners, Jean-Luc"https://zbmath.org/authors/?q=ai:lehners.jean-lucSummary: There is increasing evidence from string theory that effective field theories are only reliable over approximately sub-Planckian field excursions. The two most promising effective models for early universe cosmology, inflation and ekpyrosis, are mechanisms that, in order to address cosmological puzzles, must operate over vast expansion/energy ranges. This suggests that it might be appropriate to describe them using scaling laws. Here we combine these two ideas and demonstrate that they drive inflation and ekpyrosis to their extremes: inflation must start at ultra-slow-roll, and ekpyrosis at ultra-fast-roll. At face value, the implied spectra are overly tilted to the red, although in both cases minor departures from pure scale freedom bring the spectral indices within current observational bounds. These models predict a significant spectral running at a level detectable in the near future (\(\alpha_s \approx -10^{-3}\)). Ekpyrotic models with minimal coupling are nevertheless ruled out, as they lead to levels of non-Gaussianity that are at least an order of magnitude too large. No such restrictions apply to models with a kinetic coupling between the two ekpyrotic scalar fields, and these remain the most promising ekpyrotic models.
An additional swampland criterion that was recently proposed for the slope of the scalar field potential would however rule out all ultra-slow-roll models of inflation. Finally, we speculate on the existence of corresponding restrictions on the slope at negative potential values, which might lead to similarly severe constraints on ekpyrotic models.The swampland: introduction and reviewhttps://zbmath.org/1527.830962024-02-28T19:32:02.718555Z"Palti, Eran"https://zbmath.org/authors/?q=ai:palti.eranSummary: The Swampland program aims to distinguish effective theories which can be completed into quantum gravity in the ultraviolet from those which cannot. This article forms an introduction to the field, assuming only a knowledge of quantum field theory and general relativity. It also forms a comprehensive review, covering the range of ideas that are part of the field, from the Weak Gravity Conjecture, through compactifications of String Theory, to the de Sitter conjecture.
{\copyright} 2019 WILEY-VCH Verlag GmbH \& Co. KGaA, WeinheimHypernatural inflationhttps://zbmath.org/1527.830972024-02-28T19:32:02.718555Z"Linde, Andrei"https://zbmath.org/authors/?q=ai:linde.andrei-d"Wang, Dong-Gang"https://zbmath.org/authors/?q=ai:wang.dong-gang.1"Welling, Yvette"https://zbmath.org/authors/?q=ai:welling.yvette.1"Yamada, Yusuke"https://zbmath.org/authors/?q=ai:yamada.yusuke"Achúcarro, Ana"https://zbmath.org/authors/?q=ai:achucarro.anaSummary: We construct a model of natural inflation in the context of \(\alpha\)-attractor supergravity, in which both the dilaton field and the axion field are light during inflation, and the inflaton may be a combination of the two. The T-model version of this theory is defined on the Poincaré disk with radius \(|Z| = 1\). It describes a Mexican hat potential with the flat axion direction corresponding to a circle of radius \(|Z| < 1\). The axion decay constant \(f_a\) in this theory can be exponentially large because of the hyperbolic geometry of the Poincaré disk. Depending on initial conditions, this model may describe \(\alpha\)-attractor inflation driven by the radial component of the inflaton field, natural inflation driven by the axion field, or a sequence of these two regimes. We also construct the E-model version of this theory, which have similar properties. In addition, we describe generalized \(\alpha\)-attractor models where the potential can be singular at the boundary of the moduli space, and show that they can provide a simple solution for the problem of initial conditions for the models with plateau potentials.Pole inflation in Jordan frame supergravityhttps://zbmath.org/1527.830982024-02-28T19:32:02.718555Z"Saikawa, Ken'ichi"https://zbmath.org/authors/?q=ai:saikawa.kenichi"Yamaguchi, Masahide"https://zbmath.org/authors/?q=ai:yamaguchi.masahide"Yamashita, Yasuho"https://zbmath.org/authors/?q=ai:yamashita.yasuho"Yoshida, Daisuke"https://zbmath.org/authors/?q=ai:yoshida.daisukeSummary: We investigate inflation models in Jordan frame supergravity, in which an inflaton non-minimally couples to the scalar curvature. By imposing the condition that an inflaton would have the canonical kinetic term in the Jordan frame, we construct inflation models with asymptotically flat potential through pole inflation technique and discuss their relation to the models based on Einstein frame supergravity. We also show that the model proposed by Ferrara et al. has special position and the relation between the Kähler potential and the frame function is uniquely determined by requiring that scalars take the canonical kinetic terms in the Jordan frame and that a frame function consists only of a holomorphic term (and its anti-holomorphic counterpart) for symmetry breaking terms. Our case corresponds to relaxing the latter condition.Power-counting during single-field slow-roll inflationhttps://zbmath.org/1527.830992024-02-28T19:32:02.718555Z"Adshead, Peter"https://zbmath.org/authors/?q=ai:adshead.peter"Burgess, C. P."https://zbmath.org/authors/?q=ai:burgess.clifford-p|burgess.cliff-p"Holman, R."https://zbmath.org/authors/?q=ai:holman.r-a|holman.richard"Shandera, Sarah"https://zbmath.org/authors/?q=ai:shandera.sarahSummary: We elucidate the counting of the relevant small parameters in inflationary perturbation theory. Doing this allows for an explicit delineation of the domain of validity of the semi-classical approximation to gravity used in the calculation of inflationary correlation functions. We derive an expression for the dependence of correlation functions of inflationary perturbations on the slow-roll parameter \(\epsilon = -\dot{H}/H^2\), as well as on \(H/M_p\), where \(H\) is the Hubble parameter during inflation. Our analysis is valid for single-field models in which the inflaton can traverse a Planck-sized range in field values and where all slow-roll parameters have approximately the same magnitude. As an application, we use our expression to seek the boundaries of the domain of validity of inflationary perturbation theory for regimes where this is potentially problematic: models with small speed of sound and models allowing eternal inflation.Phenomenology of fermion production during axion inflationhttps://zbmath.org/1527.831002024-02-28T19:32:02.718555Z"Adshead, Peter"https://zbmath.org/authors/?q=ai:adshead.peter"Pearce, Lauren"https://zbmath.org/authors/?q=ai:pearce.lauren"Peloso, Marco"https://zbmath.org/authors/?q=ai:peloso.marco"Roberts, Michael A."https://zbmath.org/authors/?q=ai:roberts.michael-a.1"Sorbo, Lorenzo"https://zbmath.org/authors/?q=ai:sorbo.lorenzoSummary: We study the production of fermions through a derivative coupling with a pseudoscalar inflaton and the effects of the produced fermions on the scalar primordial perturbations. We present analytic results for the modification of the scalar power spectrum due to the produced fermions, and we estimate the amplitude of the non-Gaussianities in the equilateral regime. Remarkably, we find a regime where the effect of the fermions gives the dominant contribution to the scalar spectrum while the amplitude of the bispectrum is small and in agreement with observation. We also note the existence of a regime in which the backreaction of the fermions on the evolution of the zero-mode of the inflaton can lead to inflation even if the potential of the inflaton is steep and does not satisfy the slow-roll conditions.Tensor non-Gaussianity from axion-gauge-fields dynamics: parameter searchhttps://zbmath.org/1527.831012024-02-28T19:32:02.718555Z"Agrawal, Aniket"https://zbmath.org/authors/?q=ai:agrawal.aniket"Fujita, Tomohiro"https://zbmath.org/authors/?q=ai:fujita.tomohiro"Komatsu, Eiichiro"https://zbmath.org/authors/?q=ai:komatsu.eiichiroSummary: We calculate the bispectrum of scale-invariant tensor modes sourced by spectator SU(2) gauge fields during inflation in a model containing a scalar inflaton, a pseudoscalar axion and SU(2) gauge fields. A large bispectrum is generated in this model at tree-level as the gauge fields contain a tensor degree of freedom, and its production is dominated by self-coupling of the gauge fields. This is a unique feature of non-Abelian gauge theory. The shape of the tensor bispectrum is approximately an equilateral shape for \(3 \lesssim m_Q \lesssim 4\), where \(m_Q\) is an effective dimensionless mass of the SU(2) field normalised by the Hubble expansion rate during inflation. The amplitude of non-Gaussianity of the tensor modes, characterised by the ratio \(B_h/P^2_h\), is inversely proportional to the energy density fraction of the gauge field. This ratio can be much greater than unity, whereas the ratio from the vacuum fluctuation of the metric is of order unity. The bispectrum is effective at constraining large \(m_Q\) regions of the parameter space, whereas the power spectrum constrains small \(m_Q\) regions.Systematics of constant roll inflationhttps://zbmath.org/1527.831022024-02-28T19:32:02.718555Z"Anguelova, Lilia"https://zbmath.org/authors/?q=ai:anguelova.lilia"Suranyi, Peter"https://zbmath.org/authors/?q=ai:suranyi.peter"Wijewardhana, L. C. R."https://zbmath.org/authors/?q=ai:wijewardhana.l-c-rohanaSummary: We study constant roll inflation systematically. This is a regime, in which the slow roll approximation can be violated. It has long been thought that this approximation is necessary for agreement with observations. However, recently it was understood that there can be inflationary models with a constant, and not necessarily small, rate of roll that are both stable \textit{and} compatible with the observational constraint \(n_s \approx 1\). We investigate systematically the condition for such a constant-roll regime. In the process, we find a whole new class of inflationary models, in addition to the known solutions. We show that the new models are stable under scalar perturbations. Finally, we find a part of their parameter space, in which they produce a nearly scale-invariant scalar power spectrum, as needed for observational viability.Constant-roll inflation in \(f(T)\) teleparallel gravityhttps://zbmath.org/1527.831032024-02-28T19:32:02.718555Z"Awad, A."https://zbmath.org/authors/?q=ai:awad.adel-m-m"Hanafy, W. El"https://zbmath.org/authors/?q=ai:hanafy.w-el"Nashed, G. G. L."https://zbmath.org/authors/?q=ai:nashed.gamal-g-l"Odintsov, S. D."https://zbmath.org/authors/?q=ai:odintsov.sergei-d"Oikonomou, V. K."https://zbmath.org/authors/?q=ai:oikonomou.vasilis-kSummary: We investigate in detail the implications of the constant-roll condition on the inflationary era of a scalar field coupled to a teleparallel \(f(T)\) gravity. The resulting cosmological equations constitute a reconstruction technique which enables us to find either the \(f(T)\) gravity which corresponds to a given cosmological evolution, or the Hubble rate of the cosmological evolution generated by a fixed \(f(T)\) gravity. We also analyze in some detail the phase space of the constant-roll teleparallel gravity and we discuss the physical significance of the resulting fixed points and trajectories. Also we calculate the observational indices of a theory with given \(f(T)\) gravity, and we discuss all the implications of the constant-roll condition on these. As we demonstrate, the resulting theory can be compatible with the current observational data, for a wide range of values of the free parameters of the theory.Phase portraits of general \(f(T)\) cosmologyhttps://zbmath.org/1527.831042024-02-28T19:32:02.718555Z"Awad, A."https://zbmath.org/authors/?q=ai:awad.adel-m-m"Hanafy, W. El"https://zbmath.org/authors/?q=ai:el-hanafy.w"Nashed, G. G. L."https://zbmath.org/authors/?q=ai:nashed.gamal-g-l"Saridakis, Emmanuel N."https://zbmath.org/authors/?q=ai:saridakis.emmanuel-nSummary: We use dynamical system methods to explore the general behaviour of \(f(T)\) cosmology. In contrast to the standard applications of dynamical analysis, we present a way to transform the equations into a one-dimensional autonomous system, taking advantage of the crucial property that the torsion scalar in flat FRW geometry is just a function of the Hubble function, thus the field equations include only up to first derivatives of it, and therefore in a general \(f(T)\) cosmological scenario every quantity is expressed only in terms of the Hubble function. The great advantage is that for one-dimensional systems it is easy to construct the phase space portraits, and thus extract information and explore in detail the features and possible behaviours of \(f(T)\) cosmology. We utilize the phase space portraits and we show that \(f(T)\) cosmology can describe the universe evolution in agreement with observations, namely starting from a Big Bang singularity, evolving into the subsequent thermal history and the matter domination, entering into a late-time accelerated expansion, and resulting to the de Sitter phase in the far future. Nevertheless, \(f(T)\) cosmology can present a rich class of more exotic behaviours, such as the cosmological bounce and turnaround, the phantom-divide crossing, the Big Brake and the Big Crunch, and it may exhibit various singularities, including the non-harmful ones of type II and type IV. We study the phase space of three specific viable \(f(T)\) models offering a complete picture. Moreover, we present a new model of \(f(T)\) gravity that can lead to a universe in agreement with observations, free of perturbative instabilities, and applying the Om(z) diagnostic test we confirm that it is in agreement with the combination of SNIa, BAO and CMB data at \(1\sigma\) confidence level.Recovering \(P(X)\) from a canonical complex fieldhttps://zbmath.org/1527.831052024-02-28T19:32:02.718555Z"Babichev, Eugeny"https://zbmath.org/authors/?q=ai:babichev.eugeny"Ramazanov, Sabir"https://zbmath.org/authors/?q=ai:ramazanov.sabir"Vikman, Alexander"https://zbmath.org/authors/?q=ai:vikman.alexanderSummary: We study the correspondence between models of a self-interacting canonical complex scalar field and \(P(X)\)-theories/shift-symmetric k-essence. Both describe the same background cosmological dynamics, provided that the amplitude of the complex scalar is frozen modulo the Hubble drag. We compare perturbations in these two theories on top of a fixed cosmological background. The dispersion relation for the complex scalar has two branches. In the small momentum limit, one of these branches coincides with the dispersion relation of the \(P(X)\)-theory. Hence, the low momentum phase velocity agrees with the sound speed in the corresponding \(P(X)\)-theory. The behavior of high frequency modes associated with the second branch of the dispersion relation depends on the value of the sound speed. In the subluminal case, the second branch has a mass gap. On the contrary, in the superluminal case, this branch is vulnerable to a tachyonic instability. We also discuss the special case of the \(P(X)\)-theories with an imaginary sound speed leading to the catastrophic gradient instability. The complex field models provide with a cutoff on the momenta involved in the instability.The role of fluctuation-dissipation dynamics in setting initial conditions for inflationhttps://zbmath.org/1527.831062024-02-28T19:32:02.718555Z"Bastero-Gil, Mar"https://zbmath.org/authors/?q=ai:bastero-gil.mar"Berera, Arjun"https://zbmath.org/authors/?q=ai:berera.arjun"Brandenberger, Robert"https://zbmath.org/authors/?q=ai:brandenberger.robert-h"Moss, Ian G."https://zbmath.org/authors/?q=ai:moss.ian-g"Ramos, Rudnei O."https://zbmath.org/authors/?q=ai:ramos.rudnei-o"Rosa, João G."https://zbmath.org/authors/?q=ai:rosa.joao-gSummary: We study the problem of initial conditions for slow-roll inflation along a plateau-like scalar potential within the framework of fluctuation-dissipation dynamics. We consider, in particular, that inflation was preceded by a radiation-dominated epoch where the inflaton is coupled to light degrees of freedom and may reach a near-equilibrium state. We show that the homogeneous field component can be sufficiently localized at the origin to trigger a period of slow-roll if the interactions between the inflaton and the thermal degrees of freedom are sufficiently strong and argue that this does not necessarily spoil the flatness of the potential at the quantum level. We further conclude that the inflaton can still be held at the origin after its potential begins to dominate the energy balance, leading to a period of thermal inflation. This then suppresses the effects of nonlinear interactions between the homogeneous and inhomogeneous field modes that could prevent the former from entering a slow-roll regime. Finally, we discuss the possibility of an early period of chaotic inflation, at large field values, followed by a first stage of reheating and subsequently by a second inflationary epoch along the plateau about the origin. This scenario could prevent an early overclosure of the Universe, at the same time yielding a low tensor-to-scalar ratio in agreement with observations.Quantum to classical transition in the Hořava-Lifshitz quantum cosmologyhttps://zbmath.org/1527.831072024-02-28T19:32:02.718555Z"Bernardini, A. E."https://zbmath.org/authors/?q=ai:bernardini.alex-e"Leal, P."https://zbmath.org/authors/?q=ai:leal.p"Bertolami, O."https://zbmath.org/authors/?q=ai:bertolami.orfeuSummary: A quasi-Gaussian quantum superposition of Hořava-Lifshitz (HL) stationary states is built in order to describe the transition of the quantum cosmological problem to the related classical dynamics. The obtained HL phase-space superposed Wigner function and its associated Wigner currents describe the conditions for the matching between classical and quantum phase-space trajectories. The matching quantum superposition parameter is associated to the total energy of the classical trajectory which, at the same time, drives the engendered Wigner function to the classical stationary regime. Through the analysis of the Wigner flows, the quantum fluctuations that distort the classical regime can be quantified as a measure of (non)classicality. Finally, the modifications to the Wigner currents due to the inclusion of perturbative potentials are computed in the HL quantum cosmological context. In particular, the inclusion of a cosmological constant provides complementary information that allows for connecting the age of the Universe with the overall stiff matter density profile.On the robustness of the primordial power spectrum in renormalized Higgs inflationhttps://zbmath.org/1527.831082024-02-28T19:32:02.718555Z"Bezrukov, Fedor"https://zbmath.org/authors/?q=ai:bezrukov.fedor"Pauly, Martin"https://zbmath.org/authors/?q=ai:pauly.martin"Rubio, Javier"https://zbmath.org/authors/?q=ai:rubio.javierSummary: We study the cosmological consequences of higher-dimensional operators respecting the asymptotic symmetries of the tree-level Higgs inflation action. The main contribution of these operators to the renormalization group enhanced potential is localized in a compact field range, whose upper limit is close to the end of inflation. The spectrum of primordial fluctuations in the so-called \textit{universal regime} turns out to be almost insensitive to radiative corrections and in excellent agreement with the present cosmological data. However, higher-dimensional operators can play an important role in \textit{critical Higgs inflation} scenarios containing a quasi-inflection point along the inflationary trajectory. The interplay of radiative corrections with this quasi-inflection point may translate into a sizable modification of the inflationary observables.Manyfield inflation in random potentialshttps://zbmath.org/1527.831092024-02-28T19:32:02.718555Z"Bjorkmo, Theodor"https://zbmath.org/authors/?q=ai:bjorkmo.theodor"Marsh, M. C. David"https://zbmath.org/authors/?q=ai:marsh.m-c-davidSummary: We construct models of inflation with many randomly interacting fields and use these to study the generation of cosmological observables. We model the potentials as multi-dimensional Gaussian random fields (GRFs) and identify powerful algebraic simplifications that, for the first time, make it possible to access the manyfield limit of inflation in GRF potentials. Focussing on small-field, slow-roll, approximate saddle-point inflation in potentials with structure on sub-Planckian scales, we construct explicit examples involving up to 100 fields and generate statistical ensembles comprising of 164,000 models involving 5 to 50 fields. For the subset of these that support at least sixty e-folds of inflation, we use the 'transport method' and \(\delta N\) formalism to determine the predictions for cosmological observables at the end of inflation, including the power spectrum and the local non-Gaussianities of the primordial perturbations. We find three key results: i) Planck compatibility is not rare, but future experiments may rule out this class of models; ii) In the manyfield limit, the predictions from these models agree well with, but are sharper than, previous results derived using potentials constructed through non-equilibrium Random Matrix Theory; iii) Despite substantial multifield effects, non-Gaussianities are typically very small: \(f_{\mathrm{NL}}^{\mathrm{loc}} \ll 1\). We conclude that many of the 'generic predictions' of single-field inflation can be emergent features of complex inflation models.Quasiclassical model of inhomogeneous cosmologyhttps://zbmath.org/1527.831102024-02-28T19:32:02.718555Z"Bojowald, Martin"https://zbmath.org/authors/?q=ai:bojowald.martin"Hancock, Freddy"https://zbmath.org/authors/?q=ai:hancock.freddySummary: Fluctuation terms and higher moments of a quantum state imply corrections to the classical equations of motion that may have implications in early-Universe cosmology, for instance in the state-dependent form of effective potentials. In addition, space-time properties are relevant in cosmology, in particular when combined with quantum corrections required to maintain general covariance in a consistent way. Here, an extension of previous investigations of static quasiclassical space-time models to dynamical ones is presented, describing the evolution of one-dimensional space as in the classical Lemaitre-Tolman-Bondi models. The corresponding spatial metric has two independent components, both of which are in general subject to quantum fluctuations. The main result is that individual moments from both components are indeed required for general covariance to be maintained at a semiclassical level, while quantum correlations between the components are less relevant.Quantum entanglement in multi-field inflationhttps://zbmath.org/1527.831112024-02-28T19:32:02.718555Z"Bolis, Nadia"https://zbmath.org/authors/?q=ai:bolis.nadia"Fujita, Tomohiro"https://zbmath.org/authors/?q=ai:fujita.tomohiro"Mizuno, Shuntaro"https://zbmath.org/authors/?q=ai:mizuno.shuntaro.1"Mukohyama, Shinji"https://zbmath.org/authors/?q=ai:mukohyama.shinji.4Summary: We study the emergence of quantum entanglement in multi-field inflation. In this scenario, the perturbations of one field contribute to the observable curvature perturbation, while multi-field dynamics with the other fields affect the curvature perturbation through particle production and entanglement. We develop a general formalism which defines the quantum entanglement between the perturbations of the multiple fields both in the Heisenberg and Schrödinger pictures, and show that entanglement between different fields can arise dynamically in the context of multi-field inflationary scenarios. We also present a simple model in which a sudden change in the kinetic matrix of the scalar fields generates entanglement and an oscillatory feature appears in the power spectrum of the inflaton perturbation.Quantum behavior of the ``little sibling'' of the big rip induced by a three-form fieldhttps://zbmath.org/1527.831122024-02-28T19:32:02.718555Z"Bouhmadi-López, Mariam"https://zbmath.org/authors/?q=ai:bouhmadi-lopez.mariam"Brizuela, David"https://zbmath.org/authors/?q=ai:brizuela.david"Garay, Iñaki"https://zbmath.org/authors/?q=ai:garay.inakiSummary: A canonical quantization à la Wheeler-DeWitt is performed for a model of three-form fields in a homogeneous and isotropic universe. We start by carrying out the Hamiltonian formalism of this cosmological model. We then apply this formalism to a Little Sibling of the Big Rip (LSBR), an abrupt event milder than a Big Rip and that is known to be generic to several minimally coupled three-form fields for a variety of potentials. We obtain a set of analytical solutions of the Wheeler-DeWitt equation using different analytical approximations and explore the physical consequences of them. It turns out that there are quantum states where the wave function of the universe vanishes, i.e. the DeWitt condition is fulfilled for them. Given that this happens only for some subset of solutions of the Wheeler-DeWitt equation, this points out that the matter inducing the LSBR is equally important in the process as, it has been previously shown, a minimally coupled phantom scalar field feeding classically a LSBR is smoothed at the quantum level, i.e. all the quantum states lead to a vanishing wave function.Arbitrary static, spherically symmetric space-times as solutions of scalar-tensor gravityhttps://zbmath.org/1527.831132024-02-28T19:32:02.718555Z"Bronnikov, K. A."https://zbmath.org/authors/?q=ai:bronnikov.kirill-a"Badalov, Kodir"https://zbmath.org/authors/?q=ai:badalov.kodir"Ibadov, Rustam"https://zbmath.org/authors/?q=ai:ibadov.rustamSummary: It is shown that an arbitrary static, spherically symmetric metric can be presented as an exact solution of a scalar-tensor theory (STT) of gravity with certain nonminimal coupling function \(f(\phi)\) and potential \(U(\phi)\). The scalar field in this representation can change its nature from canonical to phantom on certain coordinate spheres. This representation, however, is valid in general not in the full range of the radial coordinate but only piecewise. Two examples of STT representations are discussed: for the Reissner-Nordström metric and for the Simpson-Visser regularization of the Schwarzschild metric (the so-called black bounce space-time).Corrigendum to: ``Emergent metric and geodesic analysis in cosmological solutions of (torsion-free) polynomial affine gravity''https://zbmath.org/1527.831142024-02-28T19:32:02.718555Z"Castillo-Felisola, Oscar"https://zbmath.org/authors/?q=ai:castillo-felisola.oscar"Grez, Bastian"https://zbmath.org/authors/?q=ai:grez.bastian"Orellana, Oscar"https://zbmath.org/authors/?q=ai:orellana.oscar-f"Perdiguero, José"https://zbmath.org/authors/?q=ai:perdiguero.jose"Skirzewski, Aureliano"https://zbmath.org/authors/?q=ai:skirzewski.aureliano"Zerwekh, Alfonso R."https://zbmath.org/authors/?q=ai:zerwekh.alfonso-rFrom the text: In the original article, the reported field equations for the \(\mathcal{B}\)-field are inconsistent with the trace-less condition for \(\mathcal{B}\).
Corrigendum to the authors' paper [ibid. 37, No. 7, Article ID 075013, 30 p. (2020; Zbl 1479.83242)].Electroweak phase transition and entropy release in the early universehttps://zbmath.org/1527.831152024-02-28T19:32:02.718555Z"Chaudhuri, A."https://zbmath.org/authors/?q=ai:chaudhuri.arin|chaudhuri.atal|chaudhuri.anirban|chaudhuri.anita|chaudhuri.anamitra|chaudhuri.abhik|chaudhuri.adhip|chaudhuri.anuja-ray|chaudhuri.anamika|chaudhuri.arnab|chaudhuri.abhijit|chaudhuri.amrita-ray|chaudhuri.a-k|chaudhuri.atasi-ray|chaudhuri.arindam|chaudhuri.arup-saha|chaudhuri.anupam|chaudhuri.ananish|chaudhuri.avik|chaudhuri.atanu|chaudhuri.a-roy|chaudhuri.adittya|chaudhuri.arijit"Dolgov, A."https://zbmath.org/authors/?q=ai:dolgov.alexandre-dmitrievich|dolgov.a-aSummary: It is shown that the vacuum-like energy of the Higgs potential at non-zero temperatures leads, in the course of the cosmological expansion, to a small but non-negligible rise of the entropy density in the comoving volume. This increase is calculated in the frameworks of the minimal standard model. The result can have a noticeable effect on the outcome of baryo-through-leptogenesis.Connections between Minkowski and cosmological correlation functionshttps://zbmath.org/1527.831162024-02-28T19:32:02.718555Z"Chu, Shek Kit"https://zbmath.org/authors/?q=ai:chu.shek-kit.1"Lee, Mang Hei Gordon"https://zbmath.org/authors/?q=ai:lee.mang-hei-gordon"Lu, Shiyun"https://zbmath.org/authors/?q=ai:lu.shiyun"Tong, Xi"https://zbmath.org/authors/?q=ai:tong.xi"Wang, Yi"https://zbmath.org/authors/?q=ai:wang.yi.34"Zhou, Siyi"https://zbmath.org/authors/?q=ai:zhou.siyiSummary: We show how cosmological correlation functions of massless fields can be rewritten in terms of Minkowski correlation functions, by extracting symmetry-breaking operators from the cosmological correlators. This technique simplifies some cosmological calculations. Also, known properties of Minkowski correlation functions can be translated to non-trivial properties of cosmological correlations. To illustrate this idea, inflation to Minkowski and matter bounce to Minkowski relations are presented for the interactions of general single field inflation. And a Minkowski recursion relation is translated to a novel relation for inflation.New perspectives on constant-roll inflationhttps://zbmath.org/1527.831172024-02-28T19:32:02.718555Z"Cicciarella, Francesco"https://zbmath.org/authors/?q=ai:cicciarella.francesco"Mabillard, Joel"https://zbmath.org/authors/?q=ai:mabillard.joel"Pieroni, Mauro"https://zbmath.org/authors/?q=ai:pieroni.mauroSummary: We study constant-roll inflation using the \(\beta\)-function formalism. We show that the constant rate of the inflaton roll is translated into a first order differential equation for the \(\beta\)-function which can be solved easily. The solutions to this equation correspond to the usual constant-roll models. We then construct, by perturbing these exact solutions, more general classes of models that satisfy the constant-roll equation asymptotically. In the case of an asymptotic power law solution, these corrections naturally provide an end to the inflationary phase. Interestingly, while from a theoretical point of view (in particular in terms of the holographic interpretation) these models are intrinsically different from standard slow-roll inflation, they may have phenomenological predictions in good agreement with present cosmological data.The 'unitarity problem' of Higgs inflation in the light of collapse dynamicshttps://zbmath.org/1527.831182024-02-28T19:32:02.718555Z"Das, Suratna"https://zbmath.org/authors/?q=ai:das.suratnaSummary: Higgs inflation scenario is one of the most compelling models of inflation at present time. It not only explains the observed data well, but also provides means to include the inflaton field within the well understood Standard Model of particle physics, without invoking any need for its extension. Despite this, due to the requirement of large non-minimal coupling to the curvature scalar of the inflaton field, or in this case the Higgs field, this model suffers from a problem often called as the `unitarity' or the `naturalness' problem. On the other hand, to address the longstanding `interpretational issue' of quantum to classical transition of the primordial modes, the collapse dynamics of quantum mechanics has recently been included into the inflationary mechanism. We show that inclusion of such collapse mechanism in Higgs inflation helps alleviate the `unitarity problem' to a great deal.Seven lessons from manyfield inflation in random potentialshttps://zbmath.org/1527.831192024-02-28T19:32:02.718555Z"Dias, Mafalda"https://zbmath.org/authors/?q=ai:dias.mafalda"Frazer, Jonathan"https://zbmath.org/authors/?q=ai:frazer.jonathan"Marsh, M. C. David"https://zbmath.org/authors/?q=ai:marsh.m-c-davidSummary: We study inflation in models with many interacting fields subject to randomly generated scalar potentials. We use methods from non-equilibrium random matrix theory to construct the potentials and an adaption of the ``transport method'' to evolve the two-point correlators during inflation. This construction allows, for the first time, for an explicit study of models with up to 100 interacting fields supporting a period of ``approximately saddle-point'' inflation. We determine the statistical predictions for observables by generating over 30,000 models with 2--100 fields supporting at least 60 efolds of inflation. These studies lead us to seven lessons: \textit{i)} Manyfield inflation is not single-field inflation, \textit{ii)} The larger the number of fields, the simpler and sharper the predictions, \textit{iii)} Planck compatibility is not rare, but future experiments may rule out this class of models, \textit{iv)} The smoother the potentials, the sharper the predictions, \textit{v)} Hyperparameters can transition from stiff to sloppy, \textit{vi)} Despite tachyons, isocurvature can decay, \textit{vii)} Eigenvalue repulsion drives the predictions. We conclude that many of the ``generic predictions'' of single-field inflation can be emergent features of complex inflation models.Non-Gaussianity from axion-gauge fields interactions during inflationhttps://zbmath.org/1527.831202024-02-28T19:32:02.718555Z"Dimastrogiovanni, Emanuela"https://zbmath.org/authors/?q=ai:dimastrogiovanni.emanuela"Fasiello, Matteo"https://zbmath.org/authors/?q=ai:fasiello.matteo"Hardwick, Robert J."https://zbmath.org/authors/?q=ai:hardwick.robert-j"Assadullahi, Hooshyar"https://zbmath.org/authors/?q=ai:assadullahi.hooshyar"Koyama, Kazuya"https://zbmath.org/authors/?q=ai:koyama.kazuya"Wands, David"https://zbmath.org/authors/?q=ai:wands.davidSummary: We study the scalar-tensor-tensor non-Gaussian signal in an inflationary model comprising also an axion coupled with SU(2) gauge fields. In this set-up, metric fluctuations are sourced by the gauge fields already at the linear level providing an enhanced chiral gravitational waves spectrum. The same mechanism is at work in generating an amplitude for the three-point function that is parametrically larger than in standard single-field inflation.Non-minimal gravitational reheating during kinationhttps://zbmath.org/1527.831212024-02-28T19:32:02.718555Z"Dimopoulos, Konstantinos"https://zbmath.org/authors/?q=ai:dimopoulos.konstantinos"Markkanen, Tommi"https://zbmath.org/authors/?q=ai:markkanen.tommi.6Summary: A new mechanism is presented which can reheat the Universe in non-oscillatory models of inflation, where the inflation period is followed by a period dominated by the kinetic density for the inflaton field (kination). The mechanism considers an auxiliary field non-minimally coupled to gravity. The auxiliary field is a spectator during inflation, rendered heavy by the non-minimal coupling to gravity. During kination however, the non-minimal coupling generates a tachyonic mass, which displaces the field, until its bare mass becomes important, leading to coherent oscillations. Then, the field decays into the radiation bath of the hot big bang. The model is generic and predictive, in that the resulting reheating temperature is a function only of the model parameters (masses and couplings) and not of initial conditions. It is shown that reheating can be very efficient also when considering only the Standard Model.Gauge field and fermion production during axion inflationhttps://zbmath.org/1527.831222024-02-28T19:32:02.718555Z"Domcke, Valerie"https://zbmath.org/authors/?q=ai:domcke.valerie"Mukaida, Kyohei"https://zbmath.org/authors/?q=ai:mukaida.kyoheiSummary: We study the dual production of helical Abelian gauge fields and chiral fermions through the Chern-Simons (CS) coupling with a pseudo-scalar inflaton in the presence of a chiral anomaly. Through the CS term, the motion of the inflaton induces a tachyonic instability for one of the two helicities of the gauge field. We show that the resulting helical gauge field necessarily leads to the production of chiral fermions by deforming their Fermi sphere into discrete Landau levels. The population of the lowest Landau level leads to a chiral asymmetry as inferred from the chiral anomaly, while the higher levels are populated symmetrically through pair production. From the backreaction of the fermions on the gauge field production we derive a conservative but stringent upper bound on the magnitude of the gauge fields. Consequently, we find that the scalar perturbations sourced by these helical gauge fields, responsible for enhanced structure formation on small scales, get reduced significantly. We also discuss the fate of the primordial chiral asymmetry and of the helical gauge fields after inflation, and show that the instability in the chiral plasma tends to erase these primordial asymmetries. This result may impact scenarios where the baryon asymmetry of the Universe is connected to primordial magnetic fields.Observables for cyclic causal set cosmologieshttps://zbmath.org/1527.831232024-02-28T19:32:02.718555Z"Dowker, Fay"https://zbmath.org/authors/?q=ai:dowker.fay"Zalel, Stav"https://zbmath.org/authors/?q=ai:zalel.stavSummary: In causal set theory, cycles of cosmic expansion and collapse are modelled by causal sets with `breaks' and `posts' and a special role is played by cyclic dynamics in which the universe goes through perpetual cycles. We identify and characterise two algebras of observables for cyclic dynamics in which the causal set universe has infinitely many breaks. The first algebra is constructed from the cylinder sets associated with finite causal sets that have a single maximal element and offers a new framework for defining cyclic dynamics as random walks on a novel tree. The second algebra is generated by a collection of stem-sets and offers a physical interpretation of the observables in these models as statements about unlabelled stems with a single maximal element. There are analogous theorems for cyclic dynamics in which the causal set universe has infinitely many posts.Cosmological dynamics of mimetic gravityhttps://zbmath.org/1527.831242024-02-28T19:32:02.718555Z"Dutta, Jibitesh"https://zbmath.org/authors/?q=ai:dutta.jibitesh"Khyllep, Wompherdeiki"https://zbmath.org/authors/?q=ai:khyllep.wompherdeiki"Saridakis, Emmanuel N."https://zbmath.org/authors/?q=ai:saridakis.emmanuel-n"Tamanini, Nicola"https://zbmath.org/authors/?q=ai:tamanini.nicola"Vagnozzi, Sunny"https://zbmath.org/authors/?q=ai:vagnozzi.sunnySummary: We present a detailed investigation of the dynamical behavior of mimetic gravity with a general potential for the mimetic scalar field. Performing a phase-space and stability analysis, we show that the scenario at hand can successfully describe the thermal history of the universe, namely the successive sequence of radiation, matter, and dark-energy eras. Additionally, at late times the universe can either approach a de Sitter solution, or a scaling accelerated attractor where the dark-matter and dark-energy density parameters are of the same order, thus offering an alleviation of the cosmic coincidence problem. Applying our general analysis to various specific potential choices, including the power-law and the exponential ones, we show that mimetic gravity can be brought into good agreement with the observed behavior of the universe. Moreover, with an inverse square potential we find that mimetic gravity offers an appealing unified cosmological scenario where both dark energy and dark matter are characterized by a single scalar field, and where the cosmic coincidence problem is alleviated.Dark energy with a gradient coupling to the dark matter fluid: cosmological dynamics and structure formationhttps://zbmath.org/1527.831252024-02-28T19:32:02.718555Z"Dutta, Jibitesh"https://zbmath.org/authors/?q=ai:dutta.jibitesh"Khyllep, Wompherdeiki"https://zbmath.org/authors/?q=ai:khyllep.wompherdeiki"Tamanini, Nicola"https://zbmath.org/authors/?q=ai:tamanini.nicolaSummary: We consider scalar field models of dark energy interacting with dark matter through a coupling proportional to the contraction of the four-derivative of the scalar field with the four-velocity of the dark matter fluid. The coupling is realized at the Lagrangian level employing the formalism of Scalar-Fluid theories, which use a consistent Lagrangian approach for relativistic fluid to describe dark matter. This framework produces fully covariant field equations, from which we can derive unequivocal cosmological equations at both background and linear perturbations levels. The background evolution is analyzed in detail applying dynamical systems techniques, which allow us to find the complete asymptotic behavior of the universe given any set of model parameters and initial conditions. Furthermore we study linear cosmological perturbations investigating the growth of cosmic structures within the quasi-static approximation. We find that these interacting dark energy models give rise to interesting phenomenological dynamics, including late-time transitions from dark matter to dark energy domination, matter and accelerated scaling solutions and dynamical crossing of the phantom barrier. Moreover we obtain possible deviations from standard \(\Lambda\) CDM behavior at the linear perturbations level, which have an impact on the dynamics of structure formation and might provide characteristic observational signatures.Higgs inflation at the hilltophttps://zbmath.org/1527.831262024-02-28T19:32:02.718555Z"Enckell, Vera-Maria"https://zbmath.org/authors/?q=ai:enckell.vera-maria"Enqvist, Kari"https://zbmath.org/authors/?q=ai:enqvist.kari"Räsänen, Syksy"https://zbmath.org/authors/?q=ai:rasanen.syksy.4"Tomberg, Eemeli"https://zbmath.org/authors/?q=ai:tomberg.eemeli-sSummary: We study inflation with the non-minimally coupled Standard Model Higgs in the case when quantum corrections generate a hilltop in the potential. We consider both the metric and the Palatini formulation of general relativity. We investigate hilltop inflation in different parts of the Higgs potential and calculate predictions for CMB observables. We run the renormalization group equations up from the electroweak scale and down from the hilltop, adding a jump in-between to account for unknown corrections in the intermediate regime. Within our approximation, no viable hilltop inflation is possible for small field values, where the non-minimal coupling has no role, nor for intermediate field values. For large field values, hilltop inflation works. We find the spectral index to be \(n_s \leq 0.96\) in both the metric and the Palatini formulation, the upper bound coinciding with the tree-level result. The tensor-to-scalar ratio is \(r \leq1.2\times 10^{-3}\) in the metric case and \(r \leq2.2\times 10^{-9}\) in the Palatini case. Successful inflation is possible even when the renormalization group running is continuous with no jumps. In the metric formulation, \textit{r} is smaller than in Higgs inflation on the tree-level plateau or at the critical point, making it possible to distinguish hilltop inflation from these scenarios with next-generation CMB experiments.A fresh look at the calculation of tunneling actionshttps://zbmath.org/1527.831272024-02-28T19:32:02.718555Z"Espinosa, J. R."https://zbmath.org/authors/?q=ai:espinosa.jose-rSummary: An alternative approach to the calculation of tunneling actions, that control the exponential suppression of the decay of metastable phases, is presented. The new method circumvents the use of bounces in Euclidean space by introducing an auxiliary function, a tunneling potential \(V_t\) that connects smoothly the metastable and stable phases of the field potential \(V\). The tunneling action is obtained as the integral in field space of an action density that is a simple function of \(V_t\) and \(V\). This compact expression can be considered as a generalization of the thin-wall action to arbitrary potentials and allows a fast numerical evaluation with a precision below the percent level for typical potentials. The method can also be used to generate potentials with analytic tunneling solutions.Natural inflation with a periodic non-minimal couplinghttps://zbmath.org/1527.831282024-02-28T19:32:02.718555Z"Ferreira, Ricardo Z."https://zbmath.org/authors/?q=ai:ferreira.ricardo-z"Notari, Alessio"https://zbmath.org/authors/?q=ai:notari.alessio"Simeon, Guillem"https://zbmath.org/authors/?q=ai:simeon.guillemSummary: Natural inflation is an attractive model for primordial inflation, since the potential for the inflaton is of the pseudo Nambu-Goldstone form, \(V(\phi) = \Lambda^4[1+\cos(\phi/f)]\), and so is protected against radiative corrections. Successful inflation can be achieved if \(f \gtrsim\) few \(M_P\) and \(\Lambda \sim m_{\mathrm{GUT}}\) where \(\Lambda\) can be seen as the strong coupling scale of a given non-abelian gauge group. However, the latest observational constraints put natural inflation in some tension with data. We show here that a non-minimal coupling to gravity \(\gamma^2(\phi)R\), that respects the symmetry \(\phi \rightarrow \phi+2\pi f\) and has a simple form, proportional to the potential, can improve the agreement with cosmological data. Moreover, in certain cases, satisfactory agreement with the Planck 2018 TT, TE, EE and low P data can be achieved even for a periodicity scale of approximately \(M_p\).Patient observers and non-perturbative infrared dynamics in inflationhttps://zbmath.org/1527.831292024-02-28T19:32:02.718555Z"Ferreira, Ricardo Z."https://zbmath.org/authors/?q=ai:ferreira.ricardo-z"Sandora, McCullen"https://zbmath.org/authors/?q=ai:sandora.mccullen"Sloth, Martin S."https://zbmath.org/authors/?q=ai:sloth.martin-sSummary: We have previously derived the effect of soft graviton modes on the quantum state of de Sitter using spontaneously broken asymptotic symmetries. In the present paper we prove that this effect can be reinterpreted in terms of Bogoliubov transformations acting on the quantum state. This also enables us to address the much discussed issues regarding the observability of infrared effects in de Sitter from a new perspective. While it is commonly agreed that infrared effects are not visible to a single sub-horizon observer at late times, we argue that the question is less trivial for a \textit{patient observer} who has lived long enough to have a record of the state before the soft mode was created. Though classically there is no obstruction to measuring this effect locally, we give several indications that quantum mechanical uncertainties may censor the effect. We then apply our methods to find a non-perturbative description of the quantum state pertaining to the Page time of de Sitter, and derive with these new methods the probability distribution for the local quantum states of de Sitter and slow-roll inflation in the presence of long modes. Finally, we show that this formalism reproduces and generalizes the usual criterion for the presence of eternal inflation in general classes of slow-roll inflation.Secluded and putative flipped dark matter and Stueckelberg extensions of the standard modelhttps://zbmath.org/1527.831302024-02-28T19:32:02.718555Z"Fortes, E. C. F. S."https://zbmath.org/authors/?q=ai:fortes.e-c-f-s"Pleitez, V."https://zbmath.org/authors/?q=ai:pleitez.vicente"Stecker, F. W."https://zbmath.org/authors/?q=ai:stecker.floyd-wSummary: We consider here three dark matter models with the gauge symmetry of the standard model plus an additional local \(\mathrm{U}(1)_D\) factor. One model is truly secluded and the other two models begin flipped, but end up secluded. All of these models include one dark fermion and one vector boson that gains mass via the Stueckelberg mechanism. We show that the would be flipped models provide an example dark matter composed of ``almost least interacting particles'' (ALIPs). Such particles are therefore compatible with the constraints obtained from both laboratory measurements and astrophysical observations.Imprints of spinning particles on primordial cosmological perturbationshttps://zbmath.org/1527.831312024-02-28T19:32:02.718555Z"Franciolini, Gabriele"https://zbmath.org/authors/?q=ai:franciolini.gabriele"Kehagias, Alex"https://zbmath.org/authors/?q=ai:kehagias.alex"Riotto, Antonio"https://zbmath.org/authors/?q=ai:riotto.antonioSummary: If there exist higher-spin particles during inflation which are light compared to the Hubble rate, they may leave distinct statistical anisotropic imprints on the correlators involving scalar and graviton fluctuations. We characterise such signatures using the dS/\(\mathrm{CFT}_3\) correspondence and the operator product expansion techniques. In particular, we obtain generic results for the case of partially massless higher-spin states.Does anisotropic inflation produce a small statistical anisotropy?https://zbmath.org/1527.831322024-02-28T19:32:02.718555Z"Fujita, Tomohiro"https://zbmath.org/authors/?q=ai:fujita.tomohiro"Obata, Ippei"https://zbmath.org/authors/?q=ai:obata.ippeiSummary: Anisotropic inflation is an interesting model with an U(1) gauge field and it predicts the statistical anisotropy of the curvature perturbation characterized by a parameter \(g_*\). However, we find that the background gauge field does not follow the classical attractor solution due to the stochastic effect. We develop the stochastic formalism of a vector field and solve Langevin and Fokker-Planck equations. It is shown that this model is excluded by the CMB constraint \(g_* \leq 10^{-2}\) with a high probability about 99.999\%.Statistically anisotropic tensor modes from inflationhttps://zbmath.org/1527.831332024-02-28T19:32:02.718555Z"Fujita, Tomohiro"https://zbmath.org/authors/?q=ai:fujita.tomohiro"Obata, Ippei"https://zbmath.org/authors/?q=ai:obata.ippei"Tanaka, Takahiro"https://zbmath.org/authors/?q=ai:tanaka.takahiro"Yokoyama, Shuichiro"https://zbmath.org/authors/?q=ai:yokoyama.shuichiroSummary: We consider the inflationary universe with a spectator scalar field coupled to a U(1) gauge field and calculate curvature perturbation and gravitational waves (GWs). We find that the sourced GWs can be larger than the one from vacuum fluctuation and they are statistically anisotropic as well as linearly polarized. The GW power spectrum acquires higher multipole moments with respect to the angle \(\theta\) between a wave number \(\boldsymbol{k}\) and a background vector field as \(\mathcal{P}_h \propto (1 - \cos^2\theta + \cos^4\theta - \cos^6\theta)\) irrespective of the model parameters.Primordial fluctuations and non-Gaussianities in sidetracked inflationhttps://zbmath.org/1527.831342024-02-28T19:32:02.718555Z"Garcia-Saenz, Sebastian"https://zbmath.org/authors/?q=ai:garcia-saenz.sebastian"Renaux-Petel, Sébastien"https://zbmath.org/authors/?q=ai:renaux-petel.sebastien.2"Ronayne, John"https://zbmath.org/authors/?q=ai:ronayne.john.1Summary: Heavy scalar fields can undergo an instability during inflation as a result of their kinetic couplings with the inflaton. This is known as the geometrical destabilization of inflation, as it relies on the effect of the negative curvature of the field-space manifold overcoming the stabilizing force of the potential. This instability can drive the system away from its original path in field space into a new inflationary attractor, a scenario that we dub \textit{sidetracked inflation}. We study this second phase and its observable consequences in several classes of two-field models. We show that cosmological fluctuations exhibit varied behaviours depending on the potential and the field space geometry, and that they can be captured by single-field effective theories with either a modified dispersion relation, a reduced speed of sound, or an imaginary one -- the latter case describing a transient tachyonic growth of the fluctuations. We also numerically calculate the bispectrum with the transport approach, finding large non-Gaussianities of equilateral and orthogonal shapes. In the hyperbolic geometry the potentials of our models present a pole at the boundary of the Poincaré disk and we discuss their relationships with \(\alpha\)-attractors.Gravitational collapse in the Schrödinger-Poisson systemhttps://zbmath.org/1527.831352024-02-28T19:32:02.718555Z"Garny, M."https://zbmath.org/authors/?q=ai:garny.mathias"Konstandin, T."https://zbmath.org/authors/?q=ai:konstandin.thomasSummary: We perform a quantitative comparison between N-body simulations and the Schrödinger-Poisson system in 1+1 dimensions. In particular, we study halo formation with different initial conditions. We observe the convergence of various observables in the Planck constant \(\hbar\) and also test virialization. We discuss the generation of higher order cumulants of the particle distribution function which demonstrates that the Schrödinger-Poisson equations should not be perceived as a generalization of the dust model with quantum pressure but rather as one way of sampling the phase space of the Vlasov-Poisson system -- just as N-body simulations. Finally, we quantitatively recover the scaling behavior of the halo density profile from N-body simulations.Schwinger pair production by electric field coupled to inflatonhttps://zbmath.org/1527.831362024-02-28T19:32:02.718555Z"Geng, Jia-Jia"https://zbmath.org/authors/?q=ai:geng.jia-jia"Li, Bao-Fei"https://zbmath.org/authors/?q=ai:li.bao-fei"Soda, Jiro"https://zbmath.org/authors/?q=ai:soda.jiro"Wang, Anzhong"https://zbmath.org/authors/?q=ai:wang.anzhong"Wu, Qiang"https://zbmath.org/authors/?q=ai:wu.qiang.1"Zhu, Tao"https://zbmath.org/authors/?q=ai:zhu.taoSummary: We analytically investigate the Schwinger pair production in the de Sitter background by using \textit{the uniform asymptotic approximation method}, and show that the equation of motion in general has two turning points, and the nature of these points could be single, double, real or complex, depending on the choice of the free parameters involved in the theory. Different natures of these points lead to different electric currents. In particular, when \(\beta \equiv m^2/H^2 - 9/4\) is positive, both turning points are complex, and the electric current due to the Schwinger process is highly suppressed, where \textit{m} and \(H\) denote, respectively, the mass of the particle and the Hubble parameter. For the turning points to be real, it is necessary to have \(\beta < 0\), and the more negative of \(\beta\), the easier to produce particles. In addition, when \(\beta < 0\), we also study the particle production when the electric field \(E\) is very weak. We find that the electric current in this case is proportional to \(E^{1/2 - \sqrt{|\beta|}}\), which is strongly enhanced in the weak electric field limit when \(m < \sqrt{2}H\).Quantum computational complexity, Einstein's equations and accelerated expansion of the universehttps://zbmath.org/1527.831372024-02-28T19:32:02.718555Z"Ge, Xian-Hui"https://zbmath.org/authors/?q=ai:ge.xianhui"Wang, Bin"https://zbmath.org/authors/?q=ai:wang.bin.1Summary: We study the relation between quantum computational complexity and general relativity. The quantum computational complexity is proposed to be quantified by the shortest length of geodesic quantum curves. We examine the complexity/volume duality in a geodesic causal ball in the framework of Fermi normal coordinates and derive the full non-linear Einstein equation. Using insights from the complexity/action duality, we argue that the accelerated expansion of the universe could be driven by the quantum complexity and free from coincidence and fine-tunning problems.Cosmological perturbations in modified teleparallel gravity modelshttps://zbmath.org/1527.831382024-02-28T19:32:02.718555Z"Golovnev, Alexey"https://zbmath.org/authors/?q=ai:golovnev.alexey-v"Koivisto, Tomi"https://zbmath.org/authors/?q=ai:koivisto.tomi-sebastianSummary: Cosmological perturbations are considered in \(f(T)\) and in scalar-torsion \(f(\varphi)T\) teleparallel models of gravity. Full sets of linear perturbation equations are accurately derived and analysed at the relevant limits. Interesting features of generalisations to other teleparallel models, spatially curved backgrounds, and rotated tetrads are pointed out.Consistency relations in multi-field inflationhttps://zbmath.org/1527.831392024-02-28T19:32:02.718555Z"Gong, Jinn-Ouk"https://zbmath.org/authors/?q=ai:gong.jinn-ouk"Seo, Min-Seok"https://zbmath.org/authors/?q=ai:seo.minseokSummary: We study the consequences of spatial coordinate transformation in multi-field inflation. Among the spontaneously broken de Sitter isometries, only dilatation in the comoving gauge preserves the form of the metric and thus results in quantum-protected Slavnov-Taylor identities. We derive the corresponding consistency relations between correlation functions of cosmological perturbations in two different ways, by the connected and one-particle-irreducible Green's functions. The lowest-order consistency relations are explicitly given, and we find that even in multi-field inflation the consistency relations in the soft limit are independent of the detail of the matter sector.Dark matter scenarios with multiple spin-2 fieldshttps://zbmath.org/1527.831402024-02-28T19:32:02.718555Z"González Albornoz, N. L."https://zbmath.org/authors/?q=ai:gonzalez-albornoz.n-l"Schmidt-May, Angnis"https://zbmath.org/authors/?q=ai:schmidt-may.angnis"von Strauss, Mikael"https://zbmath.org/authors/?q=ai:von-strauss.mikaelSummary: We study ghost-free multimetric theories for \((N+1)\) tensor fields with a coupling to matter and maximal global symmetry group \(S_N \times (Z_2)^N\). Their mass spectra contain a massless mode, the graviton, and \(N\) massive spin-2 modes. One of the massive modes is distinct by being the heaviest, the remaining \((N-1)\) massive modes are simply identical copies of each other. All relevant physics can therefore be understood from the case \(N=2\). Focussing on this case, we compute the full perturbative action up to cubic order and derive several features that hold to all orders in perturbation theory. The lighter massive mode does not couple to matter and neither of the massive modes decay into massless gravitons. We propose the lighter massive particle as a candidate for dark matter and investigate its phenomenology in the parameter region where the matter coupling is dominated by the massless graviton. The relic density of massive spin-2 can originate from a freeze-in mechanism or from gravitational particle production, giving rise to two different dark matter scenarios. The allowed parameter regions are very different from those in scenarios with only one massive spin-2 field and more accessible to experiments.Fate of the true-vacuum bubbleshttps://zbmath.org/1527.831412024-02-28T19:32:02.718555Z"González, Jorge A."https://zbmath.org/authors/?q=ai:gonzalez.jorge-a"Bellorín, A."https://zbmath.org/authors/?q=ai:bellorin.a"García-Ñustes, Mónica A."https://zbmath.org/authors/?q=ai:garcia-nustes.monica-a"Guerrero, L. E."https://zbmath.org/authors/?q=ai:guerrero.laura-elena-morales"Jiménez, S."https://zbmath.org/authors/?q=ai:jimenez.sara|jimenez.s-g|jimenez.salvador|jimenez.sonia|jimenez.sergio|jimenez.salvattore|jimenez.stephen|jimenez.sandra|jimenez.santa|jimenez.silvia|jimenez.sebastian|jimenez.santiago"Marín, Juan F."https://zbmath.org/authors/?q=ai:marin.juan-f.1"Vázquez, L."https://zbmath.org/authors/?q=ai:vazquez.luis|vazquez.leonor|vazquez.luis-a|vazquez.l-vSummary: We investigate the bounce solutions in vacuum decay problems. We show that it is possible to have a stable false vacuum in a potential that is unbounded from below.\( f_{\mathrm{NL}}\)-\(g_{\mathrm{NL}}\) mixing in the matter density field at higher ordershttps://zbmath.org/1527.831422024-02-28T19:32:02.718555Z"Gressel, Hedda A."https://zbmath.org/authors/?q=ai:gressel.hedda-a"Bruni, Marco"https://zbmath.org/authors/?q=ai:bruni.marcoSummary: In this paper we examine how primordial non-Gaussianity contributes to nonlinear perturbative orders in the expansion of the density field at large scales in the matter dominated era. General Relativity is an intrinsically nonlinear theory, establishing a nonlinear relation between the metric and the density field. Representing the metric perturbations with the curvature perturbation \(\zeta\), it is known that nonlinearity produces effective non-Gaussian terms in the nonlinear perturbations of the matter density field \(\delta\), even if the primordial \(\zeta\) is Gaussian. Here we generalise these results to the case of a non-Gaussian primordial \(\zeta\). Using a standard parametrization of primordial non-Gaussianity in \(\zeta\) in terms of \(f_{\mathrm{NL}}, g_{\mathrm{NL}}, h_{\mathrm{NL}}\dots\), we show how at higher order (from third and higher) nonlinearity also produces a mixing of these contributions to the density field at large scales, e.g. both \(f_{\mathrm{NL}}\) and \(g_{\mathrm{NL}}\) contribute to the third order in \(\delta\). This is the main result of this paper. Our analysis is based on the synergy between a gradient expansion (aka long-wavelength approximation) and standard perturbation theory at higher order. In essence, mathematically the equations for the gradient expansion are equivalent to those of first order perturbation theory, thus first-order results convert into gradient expansion results and, vice versa, the gradient expansion can be used to derive results in perturbation theory at higher order and large scales.Dark energy survivals in massive gravity after GW170817: SO(3) invarianthttps://zbmath.org/1527.831432024-02-28T19:32:02.718555Z"Heisenberg, Lavinia"https://zbmath.org/authors/?q=ai:heisenberg.lavinia"Tsujikawa, Shinji"https://zbmath.org/authors/?q=ai:tsujikawa.shinjiSummary: The recent detection of the gravitational wave signal GW170817 together with an electromagnetic counterpart GRB 170817A from the merger of two neutron stars puts a stringent bound on the tensor propagation speed. This constraint can be automatically satisfied in the framework of massive gravity. In this work, we consider a general SO(3)-invariant massive gravity with five propagating degrees of freedom and derive the conditions for the absence of ghosts and Laplacian instabilities in the presence of a matter perfect fluid on the flat Friedmann-Lemaître-Robertson-Walker (FLRW) cosmological background. The graviton potential containing the dependence of three-dimensional metrics and a fiducial metric coupled to a temporal scalar field gives rise to a scenario of the late-time cosmic acceleration in which the dark energy equation of state \(w_{\mathrm{DE}}\) is equivalent to \(-1\) or varies in time. We find that the deviation from the value \(w_{\mathrm{DE}}=-1\) provides important contributions to the quantities associated with the stability conditions of tensor, vector, and scalar perturbations. In concrete models, we study the dynamics of dark energy arising from the graviton potential and show that there exist viable parameter spaces in which neither ghosts nor Laplacian instabilities are present for both \(w_{\mathrm{DE}}>-1\) and \(w_{\mathrm{DE}}<-1\). We also generally obtain the effective gravitational coupling \(G_{\mathrm{eff}}\) with non-relativistic matter as well as the gravitational slip parameter \(\eta_s\) associated with the observations of large-scale structures and weak lensing. We show that, apart from a specific case, the two quantities \(G_{\mathrm{eff}}\) and \(\eta_s\) are similar to those in general relativity for scalar perturbations deep inside the sound horizon.Calculating observables in inhomogeneous cosmologies. I: General frameworkhttps://zbmath.org/1527.831442024-02-28T19:32:02.718555Z"Hellaby, Charles"https://zbmath.org/authors/?q=ai:hellaby.charles"Walters, Anthony"https://zbmath.org/authors/?q=ai:walters.anthonySummary: We lay out a general framework for calculating the variation of a set of cosmological observables, down the past null cone of an arbitrarily placed observer, in a given arbitrary inhomogeneous metric. The observables include redshift, proper motions, area distance and redshift-space density. Of particular interest are observables that are zero in the spherically symmetric case, such as proper motions. The algorithm is based on the null geodesic equation and the geodesic deviation equation, and it is tailored to creating a practical numerical implementation. The algorithm provides a method for tracking which light rays connect moving objects to the observer at successive times. Our algorithm is applied to the particular case of the Szekeres metric. A numerical implementation has been created and some results will be presented in a subsequent paper. Future work will explore the range of possibilities.Non-perturbative results for the luminosity and area distanceshttps://zbmath.org/1527.831452024-02-28T19:32:02.718555Z"Ivanov, Dimitar"https://zbmath.org/authors/?q=ai:ivanov.dimitar"Liberati, Stefano"https://zbmath.org/authors/?q=ai:liberati.stefano"Viel, Matteo"https://zbmath.org/authors/?q=ai:viel.matteo"Visser, Matt"https://zbmath.org/authors/?q=ai:visser.mattSummary: The notion of luminosity distance is most often defined in purely FLRW (Friedmann-Lemaitre-Robertson-Walker) cosmological spacetimes, or small perturbations thereof. However, the abstract notion of luminosity distance is actually much more robust than this, and can be defined non-perturbatively in almost arbitrary spacetimes. Some quite general results are already known, in terms of \(dA_{\mathrm{observer}}/d\Omega_{\mathrm{source}}\), the cross-sectional area per unit solid angle of a null geodesic spray emitted from some source and subsequently detected by some observer. We shall reformulate these results in terms of a suitably normalized null geodesic affine parameter and the van Vleck determinant, \(\Delta_{vV}\). The contribution due to the null geodesic affine parameter is effectively the inverse square law for luminosity, and the van Vleck determinant can be viewed as providing a measure of deviations from the inverse square law. This formulation is closely related to the so-called Jacobi determinant, but the van Vleck determinant has somewhat nicer analytic properties and wider and deeper theoretical base in the general relativity, quantum physics, and quantum field theory communities. In the current article we shall concentrate on non-perturbative results, leaving near-FLRW perturbative investigation for future work.Strongly coupled quasi-single field inflationhttps://zbmath.org/1527.831462024-02-28T19:32:02.718555Z"Iyer, Aditya Varna"https://zbmath.org/authors/?q=ai:iyer.aditya-varna"Pi, Shi"https://zbmath.org/authors/?q=ai:pi.shi"Wang, Yi"https://zbmath.org/authors/?q=ai:wang.yi.34"Wang, Ziwei"https://zbmath.org/authors/?q=ai:wang.ziwei"Zhou, Siyi"https://zbmath.org/authors/?q=ai:zhou.siyiSummary: We study the power spectrum of quasi-single field inflation where strong coupling is considered. The contribution from the massive propagator can be divided into local and non-local contributions. The local one is the leading contribution and is power-law suppressed as a function of mass, while the non-local contribution is exponentially suppressed in the large mass limit. For the local contribution, it is possible to use the effective field theory approach to study the power spectrum in the strongly coupled region of the parameter space. For the non-local contribution, we developed a \textit{partial effective field theory} method to simplify the calculation: when there are multiple massive propagators, one can fully compute it after integrating out all but one massive propagator by effective field theory. The result retains the ``standard clock'' signal, which is interesting for probing the expansion history of the primordial universe and the physics of a ``cosmological collider''. The error involved compared to the full calculation is power law suppressed by the effective mass of the heavy field.On the cosmology of scalar-tensor-vector gravity theoryhttps://zbmath.org/1527.831472024-02-28T19:32:02.718555Z"Jamali, Sara"https://zbmath.org/authors/?q=ai:jamali.sara"Roshan, Mahmood"https://zbmath.org/authors/?q=ai:roshan.mahmood"Amendola, Luca"https://zbmath.org/authors/?q=ai:amendola.lucaSummary: We consider the cosmological consequences of a special scalar-tensor-vector theory of gravity, known as MOG (for MOdified Gravity), proposed to address the dark matter problem. This theory introduces two scalar fields \(G(x)\) and \(\mu(x)\), and one vector field \(\phi_\alpha(x)\), in addition to the metric tensor. We set the corresponding self-interaction potentials to zero, as in the standard form of MOG. Then using the phase space analysis in the flat Friedmann-Robertson-Walker background, we show that the theory possesses a viable sequence of cosmological epochs with acceptable time dependency for the cosmic scale factor. We also investigate MOG's potential as a dark energy model and show that extra fields in MOG cannot provide a late time accelerated expansion. Furthermore, using a dynamical system approach to solve the non-linear field equations numerically, we calculate the angular size of the sound horizon, i.e. \(\theta_s\), in MOG. We find that \(8\times 10^{-3}\mathrm{rad} < \theta_s < 8.2 \times 10^{-3}\mathrm{rad}\) which is way outside the current observational bounds. Finally, we generalize MOG to a modified form called mMOG, and we find that mMOG passes the sound-horizon constraint. However, mMOG also cannot be considered as a dark energy model unless one adds a cosmological constant, and more importantly, the matter dominated era is still slightly different from the standard case.Dark energy in scalar-vector-tensor theorieshttps://zbmath.org/1527.831482024-02-28T19:32:02.718555Z"Kase, Ryotaro"https://zbmath.org/authors/?q=ai:kase.ryotaro"Tsujikawa, Shinji"https://zbmath.org/authors/?q=ai:tsujikawa.shinjiSummary: The scalar-vector-tensor theories with second-order equations of motion can accommodate both Horndeski and generalized Proca theories as specific cases. In the presence of a perfect fluid, we study the cosmology in such a most general scheme of scalar-vector-tensor theories with parity invariance by paying particular attention to the application to dark energy. We obtain a closed-form expression of the background equations of motion by using coefficients appearing in the second-order action of scalar perturbations. We also derive conditions for the absence of ghost and Laplacian instabilities of tensor and vector perturbations and show that the existence of matter does not substantially modify the stabilities of dynamical degrees of freedom in the small-scale limit. On the other hand, the sound speed of scalar perturbations is affected by the presence of matter. Employing the quasi-static approximation for scalar perturbations deep inside the sound horizon, we derive analytic expressions of Newtonian and weak lensing gravitational potentials as well as two scalar perturbations arising from the scalar and vector fields. We apply our general framework to dark energy theories with the tensor propagation speed equivalent to the speed of light and show that the observables associated with the growth of matter perturbations and weak lensing potentials are generally affected by intrinsic vector modes and by interactions between scalar and vector fields.Algebrodynamics: super-conservative collective dynamics on a ``Unique Worldline'' and the Hubble lawhttps://zbmath.org/1527.831492024-02-28T19:32:02.718555Z"Kassandrov, V. V."https://zbmath.org/authors/?q=ai:kassandrov.vladimir-v"Khasanov, Ildus Sh."https://zbmath.org/authors/?q=ai:khasanov.ildus-shSummary: We study the properties of roots of a polynomial system of equations which define a set of identical point particles located on a Unique Worldline (UW), in the spirit of the Wheeler-Feynman's old conception. As a consequence of Vieta's formulas, a great number of conservation laws are fulfilled for collective algebraic dynamics on the UW. These, besides the canonical ones, include the laws with higher derivatives and those containing multiparticle correlation terms as well. On the other hand, such a ``super-conservative'' dynamics turns out to be manifestly Lorentz invariant and quite nontrivial. At great values of ``cosmic time'' \(t\), the roots-particles demonstrate universal recession (resembling that in the Milne's cosmology and simulating ``expansion'' of the Universe), for which the Hubble's law holds true, with the Hubble parameter inversely proportional to \(t\).Peculiarities of the motion of spinning particles in a stationary rotating cosmological modelhttps://zbmath.org/1527.831502024-02-28T19:32:02.718555Z"Krechet, V. G."https://zbmath.org/authors/?q=ai:krechet.vladimir-g"Oshurko, V. B."https://zbmath.org/authors/?q=ai:oshurko.v-b"Kisser, A. E."https://zbmath.org/authors/?q=ai:kisser.a-eSummary: The dynamics of particles described by the Dirac equation is considered in a homogeneous stationary rotating cosmological model, which is the closest generalization of Goedel's cosmological model and admits the existence of unclosed timelike lines. It is shown that, in the space-time of the rotating cosmological model, the intrinsic angular momentum of a spinor particle precesses around the axis of rotation, and the angular velocity of rotation of the cosmological model affects the mass of the spinor particle, while the spin magnetic moment of the particles can generate electromagnetic radiation called ``spin light.''Signatures of modified dispersion relation of graviton in the cosmic microwave backgroundhttps://zbmath.org/1527.831512024-02-28T19:32:02.718555Z"Li, Jun"https://zbmath.org/authors/?q=ai:li.jun.52"Huang, Qing-Guo"https://zbmath.org/authors/?q=ai:huang.qingguoSummary: The dispersion relation of graviton is a fundamental issue for fundamental physics about gravity. In this paper we investigate how the modified dispersion relation of graviton affects the cosmic microwave background (CMB) power spectra, in particular the B-mode polarization. Our results will be useful to test the dispersion relation of graviton at the energy scale around \(10^{-29}\) eV.Cosmology in Minkowski spacehttps://zbmath.org/1527.831522024-02-28T19:32:02.718555Z"Lombriser, Lucas"https://zbmath.org/authors/?q=ai:lombriser.lucasSummary: Theoretical and observational challenges to standard cosmology such as the cosmological constant problem and tensions between cosmological model parameters inferred from different observations motivate the development and search of new physics. A less radical approach to venturing beyond the standard model is the simple mathematical reformulation of our theoretical frameworks underlying it. While leaving physical measurements unaffected, this can offer a reinterpretation and even solutions of these problems. In this spirit, metric transformations are performed here that cast our Universe into different geometries. Of particular interest thereby is the formulation of cosmology in Minkowski space. Rather than an expansion of space, spatial curvature, and small-scale inhomogeneities and anisotropies, this frame exhibits a variation of mass, length and time scales across spacetime. Alternatively, this may be interpreted as an evolution of fundamental constants. As applications of this reframed cosmological picture, the naturalness of the cosmological constant is reinspected and promising candidates of geometric origin are explored for dark matter, dark energy, inflation and baryogenesis. An immediate observation thereby is the apparent absence of the cosmological constant problem in the Minkowski frame. The formalism is also applied to identify new observable signatures of conformal inhomogeneities, which have been proposed as simultaneous solution of the observational tensions in the Hubble constant, the amplitude of matter fluctuations, and the gravitational lensing amplitude of cosmic microwave background anisotropies. These are found to enhance redshifts to distant galaxy clusters and introduce a mass bias with cluster masses inferred from gravitational lensing exceeding those inferred kinematically or dynamically.Studying G-axion inflation model in light of PLANCKhttps://zbmath.org/1527.831532024-02-28T19:32:02.718555Z"Maity, Debaprasad"https://zbmath.org/authors/?q=ai:maity.debaprasad.1"Saha, Pankaj"https://zbmath.org/authors/?q=ai:saha.pankajSummary: With the Planck 2015 result, most of the well known canonical large field inflation models turned out to be strongly disfavored. Axion inflation is one of such models which is becoming marginalized with the increasing precession of CMB data. In this paper, we have shown that with a simple Galileon type modification to the marginally favored axion model calling G-axion, we can turn them into one of the most favored models with its detectable prediction of \(r\) and \(n_s\) within its PLANCK \(1\sigma\) range for a wide range of parameters. Interestingly it is this modification which plays the important role in turning the inflationary predictions to be independent of the explicit value of axion decay constant \(f\). However, dynamics after the inflation turned out to have a non-trivial dependence on \(f\). For each G-axion model there exists a critical value of \(f_c\) such that for \(f > f_c\) we have the oscillating phase after inflation and for \(f < f_c\) we have non-oscillatory phase. Therefore, we obtained a range of sub-Planckian value of model parameters which give rise to consistent inflation. However for sub-Planckian axion decay constant the inflaton field configuration appeared to be singular after the end of inflation. To reheat the universe we, therefore, employ the instant preheating mechanism at the instant of first zero crossing of the inflaton. To our surprise, the instant preheating mechanism turned out to be inefficient as opposed to usual non-oscillatory quintessence model. For another class of G-axion model with super-Planckian axion decay constant, we performed in detail the reheating constraints analysis considering the latest PLANCK result.Non Gaussianities from quantum decoherence during inflationhttps://zbmath.org/1527.831542024-02-28T19:32:02.718555Z"Martin, Jérôme"https://zbmath.org/authors/?q=ai:martin.jerome.2"Vennin, Vincent"https://zbmath.org/authors/?q=ai:vennin.vincentSummary: Inflationary cosmological perturbations of quantum-mechanical origin generically interact with all degrees of freedom present in the early Universe. Therefore, they must be viewed as an open quantum system in interaction with an environment. This implies that, under some conditions, decoherence can take place. The presence of the environment can also induce modifications in the power spectrum, thus offering an observational probe of cosmic decoherence. Here, we demonstrate that this also leads to non Gaussianities that we calculate using the Lindblad equation formalism. We show that, while the bispectrum remains zero, the four-point correlation functions become non-vanishing. Using the Cosmic Microwave Background measurements of the trispectrum by the Planck satellite, we derive constraints on the strength of the interaction between the perturbations and the environment and show that, in some regimes, they are more stringent than those arising from the power spectrum.General dynamical properties of cosmological models with nonminimal kinetic couplinghttps://zbmath.org/1527.831552024-02-28T19:32:02.718555Z"Matsumoto, Jiro"https://zbmath.org/authors/?q=ai:matsumoto.jiro"Sushkov, Sergey V."https://zbmath.org/authors/?q=ai:sushkov.sergey-vSummary: We consider cosmological dynamics in the theory of gravity with the scalar field possessing the nonminimal kinetic coupling to curvature given as \(\eta G^{\mu\nu}\phi_{,\mu}\phi_{,\nu}\), where \(\eta\) is an arbitrary coupling parameter, and the scalar potential \(V(\phi)\) which assumed to be as general as possible. With an appropriate dimensionless parametrization we represent the field equations as an autonomous dynamical system which contains ultimately only one arbitrary function \(\chi(x)= 8\pi |\eta| V(x/\sqrt{8\pi})\) with \(x=\sqrt{8\pi}\phi\). Then, assuming the rather general properties of \(\chi(x)\), we analyze stationary points and their stability, as well as all possible asymptotical regimes of the dynamical system. It has been shown that for a broad class of \(\chi(x)\) there exist attractors representing three accelerated regimes of the Universe evolution, including de Sitter expansion (or late-time inflation), the Little Rip scenario, and the Big Rip scenario. As the specific examples, we consider a power-law potential \(V(\phi)= M^4(\phi/\phi_0)^\sigma\), Higgs-like potential \(V(\phi)=\frac{\lambda}{4}(\phi^2 - \phi_0^2)^2\), and exponential potential \(V(\phi)= M^4 e^{-\phi/\phi_0}\).Vector Galileon and inflationary magnetogenesishttps://zbmath.org/1527.831562024-02-28T19:32:02.718555Z"Nandi, Debottam"https://zbmath.org/authors/?q=ai:nandi.debottam"Shankaranarayanan, S."https://zbmath.org/authors/?q=ai:shankaranarayanan.sSummary: Cosmological inflation provides the initial conditions for the structure formation. However, the origin of large-scale magnetic fields can not be addressed in this framework. The key issue for this long-standing problem is the conformal invariance of the electromagnetic (EM) field in 4-D. While many approaches have been proposed in the literature for breaking conformal invariance of the EM action, here, we provide a completely new way of looking at the modifications to the EM action and generation of primordial magnetic fields during inflation. We explicitly construct a higher derivative EM action that breaks conformal invariance by demanding three conditions -- theory be described by vector potential \(A^\mu\) and its derivatives, Gauge invariance be satisfied, and equations of motion be linear in second derivatives of vector potential. The unique feature of our model is that appreciable magnetic fields are generated at small wavelengths while tiny magnetic fields are generated at large wavelengths that are consistent with current observations.Tunneling in stochastic inflationhttps://zbmath.org/1527.831572024-02-28T19:32:02.718555Z"Noorbala, Mahdiyar"https://zbmath.org/authors/?q=ai:noorbala.mahdiyar"Vennin, Vincent"https://zbmath.org/authors/?q=ai:vennin.vincent"Assadullahi, Hooshyar"https://zbmath.org/authors/?q=ai:assadullahi.hooshyar"Firouzjahi, Hassan"https://zbmath.org/authors/?q=ai:firouzjahi.hassan"Wands, David"https://zbmath.org/authors/?q=ai:wands.david.4Summary: The relative probability to decay towards different vacua during inflation is studied. The calculation is performed in single-field slow-roll potentials using the stochastic inflation formalism. Various situations are investigated, including falling from a local maximum of the potential and escaping from a local minimum. In the latter case, our result is consistent with that of Hawking and Moss, but is applicable to any potential. The decay rates are also computed, and the case of a generic potential with multiple minima and maxima is discussed.Secondary isocurvature perturbations from acoustic reheatinghttps://zbmath.org/1527.831582024-02-28T19:32:02.718555Z"Ota, Atsuhisa"https://zbmath.org/authors/?q=ai:ota.atsuhisa"Yamaguchi, Masahide"https://zbmath.org/authors/?q=ai:yamaguchi.masahideSummary: The superhorizon (iso)curvature perturbations are conserved if the following conditions are satisfied: (i) (each) non adiabatic pressure perturbation is zero, (ii) the gradient terms are ignored, that is, at the leading order of the gradient expansion (iii) (each) total energy momentum tensor is conserved. We consider the case with the violation of the last two requirements and discuss the generation of secondary isocurvature perturbations during the late time universe. Second order gradient terms are not necessarily ignored even if we are interested in the long wavelength modes because of the convolutions which may pick products of short wavelength perturbations up. We then introduce second order conserved quantities on superhorizon scales under the conditions (i) and (iii) even in the presence of the gradient terms by employing the full second order cosmological perturbation theory. We also discuss the violation of the condition (iii), that is, the energy momentum tensor is conserved for the total system but not for each component fluid. As an example, we explicitly evaluate second order heat conduction between baryons and photons due to the weak Compton scattering, which dominates during the period just before recombination. We show that such secondary effects can be recast into the isocurvature perturbations on superhorizon scales if the local type primordial non Gaussianity exists a priori.Inflation from a nonlinear magnetic monopole field nonminimally coupled to curvaturehttps://zbmath.org/1527.831592024-02-28T19:32:02.718555Z"Otalora, Giovanni"https://zbmath.org/authors/?q=ai:otalora.giovanni"Övgün, Ali"https://zbmath.org/authors/?q=ai:ovgun.ali"Saavedra, Joel"https://zbmath.org/authors/?q=ai:saavedra.joel"Videla, Nelson"https://zbmath.org/authors/?q=ai:videla.nelsonSummary: In the context of nonminimally coupled \(f(R)\) gravity theories, we study early inflation driven by a nonlinear monopole magnetic field which is nonminimally coupled to curvature. In order to isolate the effects of the nonminimal coupling between matter and curvature we assume the pure gravitational sector to have the Einstein-Hilbert form. Thus, we study the most simple model with a nonminimal coupling function which is linear in the Ricci scalar. From an effective fluid description, we show the existence of an early exponential expansion regime of the Universe, followed by a transition to a radiation-dominated era. In particular, by applying the most recent results of the Planck collaboration we set the limits on the parameter of the nonminimal coupling, and the quotient of the nonminimal coupling and the nonlinear monopole magnetic scales. We found that these parameters must take large values in order to satisfy the observational constraints. Furthermore, by obtaining the relation for the graviton mass, we show the consistency of our results with the recent gravitational wave data GW170817 of LIGO and Virgo.Nonlinear perturbations from the coupling of the inflaton to a non-abelian gauge field, with a focus on chromo-natural inflationhttps://zbmath.org/1527.831602024-02-28T19:32:02.718555Z"Papageorgiou, Alexandros"https://zbmath.org/authors/?q=ai:papageorgiou.alexandros"Peloso, Marco"https://zbmath.org/authors/?q=ai:peloso.marco-maria|peloso.marco"Unal, Caner"https://zbmath.org/authors/?q=ai:unal.canerSummary: Several models of inflation employing a triplet of SU(2) vectors with spatially orthogonal vacuum expectation values (VEVs) have been recently proposed. One (tensor) combination \(t\) of the vector modes is amplified in some momentum range during inflation. Due to the vector VEVs, this combination mixes with gravitational waves (GW) at the linear level, resulting in a GW amplification that has been well studied in the literature. Scalar perturbations in this class of models have been so far studied only at the linear level. We perform a first step toward the nonlinear computation using as an example the original model of Chromo-Natural Inflation. We compute the contribution to the scalar power spectrum arising from the coupling of the combination \(t\) to the inflaton. This contribution is mostly controlled by a single parameter of the model (namely, the ratio between the mass of the fluctuations of the vector field and the Hubble rate), and, for a wide range of this parameter, it can significantly affect the phenomenology obtained from the linear theory. This nonlinear contribution is significantly blue, improving the comparison between the two-point function and the Cosmic Microwave Background (CMB) data. This growth can be also relevant for smaller scale phenomenology, such as large scale structure, CMB distortions, and primordial black holes.Structure formation beyond shell-crossing: nonperturbative expansions and late-time attractorshttps://zbmath.org/1527.831612024-02-28T19:32:02.718555Z"Pietroni, Massimo"https://zbmath.org/authors/?q=ai:pietroni.massimoSummary: Structure formation in 1+1 dimensions is considered, with emphasis on the effects of shell-crossing. The breakdown of the perturbative expansion beyond shell-crossing is discussed, and it is shown, in a simple example, that the perturbative series can be extended to a \textit{transseries} including nonperturbative terms. The latter converges to the exact result well beyond the range of validity of perturbation theory. The crucial role of the divergences induced by shell-crossing is discussed. They provide constraints on the structure of the transseries and act as a bridge between the perturbative and the nonperturbative sectors. Then, we show that the dynamics in the deep multistreaming regime is governed by attractors. In the case of simple initial conditions, these attractors coincide with the asymptotic configurations of the adhesion model, but in general they may differ. These results are applied to a cosmological setting, and an algorithm to build the attractor solution starting from the Zel'dovich approximation is developed. Finally, this algorithm is applied to the search of ``haloes'' and the results are compared with those obtained from the exact dynamical equations.Extended cosmology in Palatini \(f(\mathcal{R})\)-theorieshttps://zbmath.org/1527.831622024-02-28T19:32:02.718555Z"Pinto, P."https://zbmath.org/authors/?q=ai:pinto.paolo"Del Vecchio, L."https://zbmath.org/authors/?q=ai:vecchio.l-del"Fatibene, L."https://zbmath.org/authors/?q=ai:fatibene.lorenzo"Ferraris, M."https://zbmath.org/authors/?q=ai:ferraris.marcoSummary: We consider the cosmological models based on Palatini \(f(\mathcal{R})\)-theory for the function \(f(\mathcal{R}) = \alpha\mathcal{R} - \frac{\beta}{2}\mathcal{R}^2 - \frac{\gamma}{3\mathcal{R}}\), which, when only dust visible matter is considered, is called \textit{dune cosmology} in view of the shape of the function \(f(\mathcal{R}(a))\) (being \(a\) the scale factor). We discuss the meaning of solving the model, and interpret it according to the Ehlers-Pirani-Schild framework as defining a Weyl geometry on spacetime.
Accordingly, we extend the definitions of luminosity distance, proper distance, and red-shift to Weyl geometries and fit the values of parameters to SNIa data. Since the theoretical prediction is model-dependent, we argue that the fit is affected by an extra choice, namely a model for atomic clocks, which, in principle, produces observable effects. To the best of our knowledge, these effects have not being considered in the literature before.Logamediate inflation in DGP cosmology driven by a non-canonical scalar fieldhttps://zbmath.org/1527.831632024-02-28T19:32:02.718555Z"Ravanpak, A."https://zbmath.org/authors/?q=ai:ravanpak.arvin"Fadakar, G. F."https://zbmath.org/authors/?q=ai:fadakar.g-fSummary: The main properties of the logamediate inflation driven by a non-canonical scalar field in the framework of DGP braneworld gravity are investigated. Considering high energy conditions, we analytically calculate the slow-roll parameters. Then, we deal with perturbation theory and calculate the most important respective parameters, such as the scalar spectral index and the tensor-to-scalar ratio. We find that the spectrum of scalar fluctuations is always red-tilted. Also, we understand that the running in the scalar spectral index is nearly zero. Finally, we compare this inflationary scenario with the latest observational results from Planck 2018.Viable tensor-to-scalar ratio in a symmetric matter bouncehttps://zbmath.org/1527.831642024-02-28T19:32:02.718555Z"Raveendran, Rathul Nath"https://zbmath.org/authors/?q=ai:raveendran.rathul-nath"Chowdhury, Debika"https://zbmath.org/authors/?q=ai:chowdhury.debika"Sriramkumar, L."https://zbmath.org/authors/?q=ai:sriramkumar.lSummary: Matter bounces refer to scenarios wherein the universe contracts at early times as in a matter dominated epoch until the scale factor reaches a minimum, after which it starts expanding. While such scenarios are known to lead to scale invariant spectra of primordial perturbations after the bounce, the challenge has been to construct \textit{completely} symmetric bounces that lead to a tensor-to-scalar ratio which is small enough to be consistent with the recent cosmological data. In this work, we construct a model involving two scalar fields (a canonical field and a non-canonical ghost field) to drive the symmetric matter bounce and study the evolution of the scalar perturbations in the model. We find that the model can be completely described in terms of a single parameter, viz. the ratio of the scale associated with the bounce to the value of the scale factor at the bounce. We evolve the scalar perturbations numerically across the bounce and evaluate the scalar power spectra \textit{after} the bounce. We show that, while the scalar and tensor perturbation spectra are scale invariant over scales of cosmological interest, the tensor-to-scalar ratio proves to be much smaller than the current upper bound from the observations of the cosmic microwave background anisotropies by the Planck mission. We also support our numerical analysis with analytical arguments.Anisotropic tensor power spectrum at interferometer scales induced by tensor squeezed non-Gaussianityhttps://zbmath.org/1527.831652024-02-28T19:32:02.718555Z"Ricciardone, Angelo"https://zbmath.org/authors/?q=ai:ricciardone.angelo"Tasinato, Gianmassimo"https://zbmath.org/authors/?q=ai:tasinato.gianmassimoSummary: We develop a scenario of inflation with spontaneously broken time and space diffeomorphisms, with distinctive features for the primordial tensor modes. Inflationary tensor fluctuations are not conserved outside the horizon, and can acquire a mass during the inflationary epoch. They can evade the Higuchi bound around de Sitter space, thanks to interactions with the fields driving expansion. Correspondingly, the primordial stochastic gravitational wave background (SGWB) is characterised by a tuneable scale dependence, and can be detectable at interferometer scales. In this set-up, tensor non-Gaussianity can be parametrically enhanced in the squeezed limit. This induces a coupling between long and short tensor modes, leading to a specific quadrupolar anisotropy in the primordial SGWB spectrum, which can be used to build estimators for tensor non-Gaussianity. We analyse how our inflationary system can be tested with interferometers, also discussing how an interferometer can be sensitive to a primordial anisotropic SGWB.Numerically evaluating the bispectrum in curved field-space -- with \texttt{PyTransport 2.0}https://zbmath.org/1527.831662024-02-28T19:32:02.718555Z"Ronayne, John W."https://zbmath.org/authors/?q=ai:ronayne.john-w"Mulryne, David J."https://zbmath.org/authors/?q=ai:mulryne.david-jSummary: We extend the transport framework for numerically evaluating the power spectrum and bispectrum in multi-field inflation to the case of a curved field-space metric. This method naturally accounts for all sub- and super-horizon tree level effects, including those induced by the curvature of the field-space. We present an open source implementation of our equations in an extension of the publicly available \texttt{PyTransport} code. Finally we illustrate how our technique is applied to examples of inflationary models with a non-trivial field-space metric.Dynamical systems analysis of phantom dark energy modelshttps://zbmath.org/1527.831672024-02-28T19:32:02.718555Z"Roy, Nandan"https://zbmath.org/authors/?q=ai:roy.nandan.1"Bhadra, Nivedita"https://zbmath.org/authors/?q=ai:bhadra.niveditaSummary: In this work, we study the dynamical systems analysis of phantom dark energy models considering five different potentials. From the analysis of these five potentials we have found a general parametrization of the scalar field potentials which is obeyed by many other potentials. Our investigation shows that there is only one fixed point which could be the beginning of the universe. However, future destiny has many possible options. A detailed numerical analysis of the system has been presented. The observed late time behaviour in this analysis shows very good agreement with the recent observations.Heavy particle signatures in cosmological correlation functions with tensor modeshttps://zbmath.org/1527.831682024-02-28T19:32:02.718555Z"Saito, Ryo"https://zbmath.org/authors/?q=ai:saito.ryo.1"Kubota, Takahiro"https://zbmath.org/authors/?q=ai:kubota.takahiroSummary: We explore the possibility to make use of cosmological data to look for signatures of unknown heavy particles whose masses are on the order of the Hubble parameter during the time of inflation. To be more specific we take up the quasi-single field inflation model, in which the isocurvaton \(\sigma\) is supposed to be the heavy particle. We study correlation functions involving both scalar (\(\zeta\)) and tensor (\(\gamma\)) perturbations and search for imprints of the \(\sigma\)-particle effects. We make use of the technique of the effective field theory for inflation to derive the \(\zeta \sigma\) and \(\gamma \zeta \sigma\) couplings. With these couplings we compute the effects due to \(\sigma\) to the power spectrum \(\langle \zeta \zeta \rangle\) and correlations \(\langle \gamma^s \zeta \zeta \rangle\) and \(\langle \gamma^{s_1} \gamma^{s_2} \zeta \zeta \rangle\), where \(s\), \(s_1\) and \(s_2\) are the polarization indices of gravitons. Numerical analyses of the \(\sigma\)-mass effects to these correlations are presented. It is argued that future precise observations of these correlations could make it possible to measure the \(\sigma\)-mass and the strength of the \(\zeta \sigma\) and \(\gamma \zeta \sigma\) couplings. As an extension to the \(N\)-graviton case we also compute the correlations \(\langle \gamma^{s_1}\cdots\gamma^{s_N} \zeta \zeta \rangle\) and \(\langle \gamma^{s_1}\cdots\cdots\gamma^{s_{2N}} \zeta \zeta \rangle\) and their \(\sigma\)-mass effects. It is suggested that larger \(N\) correlation functions are useful to probe larger \(\sigma\)-mass.Preinflationary dynamics in loop quantum cosmology: monodromy potentialhttps://zbmath.org/1527.831692024-02-28T19:32:02.718555Z"Sharma, Manabendra"https://zbmath.org/authors/?q=ai:sharma.manabendra"Shahalam, M."https://zbmath.org/authors/?q=ai:shahalam.m"Wu, Qiang"https://zbmath.org/authors/?q=ai:wu.qiang.1"Wang, Anzhong"https://zbmath.org/authors/?q=ai:wang.anzhongSummary: In this article we explore the pre-inflationary background dynamics of an FLRW universe sourced by a scalar field with monodromy potential in LQC framework. In particular we calculate the number of e-folds, \(N_{\mathrm{inf}}\), produced during the slowly rolling phase of the inflation and find out the critical value of the ratio of the kinetic to potential energy, \(r_w^c\), at the quantum bounce that is required to produce \(N_{\mathrm{inf}} \simeq 60\). Two different monodromy potentials, namely, linear and quadratic with a modulation term are investigated to this effect. The effects on the value of \(N_{\mathrm{inf}}\) due to parameters associated with the strength, decay constant and the phase factor of the modulation term are calculated. In addition to this we present the qualitative picture of the background dynamics by carrying out a dynamical system analysis. We produce the phase portraits and carry out a detailed linear stability analysis of the finite fixed points, if any, for each of the potentials.Self-anisotropizing inflationary universe in Horndeski theory and beyondhttps://zbmath.org/1527.831702024-02-28T19:32:02.718555Z"Tahara, Hiroaki W. H."https://zbmath.org/authors/?q=ai:tahara.hiroaki-w-h"Nishi, Sakine"https://zbmath.org/authors/?q=ai:nishi.sakine"Kobayashi, Tsutomu"https://zbmath.org/authors/?q=ai:kobayashi.tsutomu"Yokoyama, Jun'ichi"https://zbmath.org/authors/?q=ai:yokoyama.junichiSummary: As opposed to Wald's cosmic no-hair theorem in general relativity, it is shown that the Horndeski theory (and its generalization) admits anisotropic inflationary attractors if the Lagrangian depends cubically on the second derivatives of the scalar field. We dub such a solution as a self-anisotropizing inflationary universe because anisotropic inflation can occur without introducing any anisotropic matter fields such as a vector field. As a concrete example of self-anisotropization we present the dynamics of a Bianchi type-I universe in the Horndeski theory.Coordinate-independent definition of relative velocity in pseudo-Riemannian space-time: implications for special caseshttps://zbmath.org/1527.831712024-02-28T19:32:02.718555Z"Ter-Kazarian, G."https://zbmath.org/authors/?q=ai:ter-kazarian.gagik|ter-kazarian.g-tSummary: Using the general solution that we recently obtained for the coordinate-independent definition of a relative velocity of a luminous source as measured along the observer's line of sight in generic pseudo-Riemannian space-time, in the present article we invoke important implications for test particles and observers in several instructive cases. We consider a test particle as a luminous object, otherwise, if it is not, we assume that a luminous source is attached to it, which has neither mass nor volume. We calculate the relative velocities in special metrics: the Minkowski metric, the test particle and observer at rest in an arbitrary stationary metric, a uniform gravitational field, a rotating reference frame, the Schwarzschild metric, a Kerr-type metrics, and the spatially homogeneous and isotropic Robertson-Walker space-time of the standard cosmological model. In the last case, it leads to a remarkable cosmological consequence that the resulting, so-called, \textit{kinetic} recession velocity of an astronomical object is always subluminal even for large redshifts of order one or more, so that it does not violate the fundamental physical principle of \textit{causality}. We also calculate the carrying-away measure of a galaxy at redshift \(z\) by the expansion of space, which proves, in particular, that the cosmological expansion of a flat 3D space is fundamentally different from the kinematics of galaxies moving in a nonexpanding flat 3D space.Statistical nature of infrared dynamics on de Sitter backgroundhttps://zbmath.org/1527.831722024-02-28T19:32:02.718555Z"Tokuda, Junsei"https://zbmath.org/authors/?q=ai:tokuda.junsei"Tanaka, Takahiro"https://zbmath.org/authors/?q=ai:tanaka.takahiroSummary: In this study, we formulate a systematic way of deriving an effective equation of motion(EoM) for long wavelength modes of a massless scalar field with a general potential \(V(\phi)\) on de Sitter background, and investigate whether or not the effective EoM can be described as a classical stochastic process. Our formulation gives an extension of the usual stochastic formalism to including sub-leading secular growth coming from the nonlinearity of short wavelength modes. Applying our formalism to \(\lambda\phi^4\) theory, we explicitly derive an effective EoM which correctly recovers the next-to-leading secularly growing part at a late time, and show that this effective EoM can be seen as a classical stochastic process. Our extended stochastic formalism can describe all secularly growing terms which appear in all correlation functions with a specific operator ordering. The restriction of the operator ordering will not be a big drawback because the commutator of a light scalar field becomes negligible at large scales owing to the squeezing.Can all the infrared secular growth really be understood as increase of classical statistical variance?https://zbmath.org/1527.831732024-02-28T19:32:02.718555Z"Tokuda, Junsei"https://zbmath.org/authors/?q=ai:tokuda.junsei"Tanaka, Takahiro"https://zbmath.org/authors/?q=ai:tanaka.takahiroSummary: It is known that in the theory of light scalar fields during inflation, correlation functions suffer from infrared (IR) divergences or large IR loop corrections, leading to the breakdown of perturbation theory. In order to understand the physical meaning of such IR enhancement, we investigate the stochastic properties of an effective equation of motion (EoM) for long-wavelength modes of a canonically normalized light scalar field \(\phi\) with a general sufficiently flat interaction potential on de Sitter background. Firstly, we provide an alternative refined derivation of the effective action for long-wavelength modes which leads to the effective EoM that correctly reproduces all the IR correlation functions in a good approximation at a late time, by integrating out short-wavelength modes. Next, under the assumption that one can neglect non-local correlations in the influence functional exceeding the coarse-graining scale, we show that the effective EoM for IR modes of the ``average field'' in Schwinger-Keldysh formalism \(\phi_c^<\) can be interpreted as a classical stochastic process in the present model.Unsuppressed primordial standard clocks in warm quasi-single field inflationhttps://zbmath.org/1527.831742024-02-28T19:32:02.718555Z"Tong, Xi"https://zbmath.org/authors/?q=ai:tong.xi"Wang, Yi"https://zbmath.org/authors/?q=ai:wang.yi.34"Zhou, Siyi"https://zbmath.org/authors/?q=ai:zhou.siyiSummary: We study the non-Gaussianities in quasi-single field inflation with a warm inflation background. The thermal effects at small scales can sufficiently enhance the magnitude of the primordial standard clock signal. This scenario offers us the possibility of probing the UV physics of the very early universe without the exponentially small Boltzmann factor when the mass of the isocurvaton is much heavier than Hubble. The thermal effects at small scales can be studied using the flat space thermal field theory, connected to an effective description using non-Bunch-Davies vacuum at large scales, with large clock signal.Kantowski-Sachs Einstein-aether scalar field cosmological modelshttps://zbmath.org/1527.831752024-02-28T19:32:02.718555Z"van den Hoogen, R. J."https://zbmath.org/authors/?q=ai:van-den-hoogen.r-j"Coley, A. A."https://zbmath.org/authors/?q=ai:coley.alan-a"Alhulaimi, B."https://zbmath.org/authors/?q=ai:alhulaimi.b"Mohandas, S."https://zbmath.org/authors/?q=ai:mohandas.shilpa"Knighton, E."https://zbmath.org/authors/?q=ai:knighton.e"O'Neil, S."https://zbmath.org/authors/?q=ai:oneil.shawn-t|oneil.seanSummary: A class of positive curvature spatially homogeneous but anisotropic cosmological models within an Einstein-aether gravitational framework are investigated. The matter source is assumed to be a scalar field which is coupled to the expansion of the aether field through a generalized exponential potential. The evolution equations are expressed in terms of expansion-normalized variables to produce an autonomous system of ordinary differential equations suitable for a numerical and qualitative analysis. An analysis of the local stability of the equilibrium points indicates that there exists a range of values of the parameters in which there exists an accelerating expansionary future attractor. In general relativity, scalar field models with an exponential potential \(V = V_0 e^{-2k\phi}\) have a late-time inflationary attractor for \(k^2<\frac{1}{2}\); however, it is found that the existence of the coupling between the aether and scalar fields allows for arbitrarily large values of the parameter \(k\).Electroweak phase transitions in multi-Higgs models: the case of trinification-inspired THDSMhttps://zbmath.org/1527.831762024-02-28T19:32:02.718555Z"Vieu, Thibault"https://zbmath.org/authors/?q=ai:vieu.thibault"Morais, António P."https://zbmath.org/authors/?q=ai:morais.antonio-p.1"Pasechnik, Roman"https://zbmath.org/authors/?q=ai:pasechnik.romanSummary: The rich vacuum structure of multi-Higgs extensions of the Standard Model (SM) may have interesting cosmological implications for the electroweak phase transition (EWPT). As an important example of such class of models, we consider a particularly simple low-energy SM-like limit of a recently proposed Grand-Unified Trinification model with the scalar sector composed of two Higgs doublets and a complex singlet and with a global U(1) family symmetry. The fermion sector of this model is extended with a family of vector-like quarks which enhances CP violation. With the current study, we aim at exploring the generic vacuum structure and uncovering the features of the EWPT in this model relevant for cosmology. We show the existence of different phase transition patterns providing strong departure from thermal equilibrium. Most of these observations are not specific to the considered model and may generically be expected in other multi-Higgs extensions of the SM.Hybrid quasi-single field inflationhttps://zbmath.org/1527.831772024-02-28T19:32:02.718555Z"Wang, Yi"https://zbmath.org/authors/?q=ai:wang.yi.34"Wu, Yi-Peng"https://zbmath.org/authors/?q=ai:wu.yi-peng"Yokoyama, Jun'ichi"https://zbmath.org/authors/?q=ai:yokoyama.junichi"Zhou, Siyi"https://zbmath.org/authors/?q=ai:zhou.siyiSummary: The decay of massive particles during inflation generates characteristic signals in the squeezed limit of the primordial bispectrum. These signals are in particular distinctive in the regime of the quasi-single field inflation, where particles are oscillating with masses comparable to the Hubble scale. We apply the investigation to a class of scalar particles that experience a so-called waterfall phase transition in the isocurvature direction driven by the symmetry-breaking mechanism based on the hybrid inflation scenario. With a time-varying mass, a novel shape of oscillatory bispectrum is presented as the signature of a waterfall phase transition during inflation.Turnaround radius in \(f(R)\) modelhttps://zbmath.org/1527.850062024-02-28T19:32:02.718555Z"Lopes, Rafael C. C."https://zbmath.org/authors/?q=ai:lopes.rafael-c-c"Voivodic, Rodrigo"https://zbmath.org/authors/?q=ai:voivodic.rodrigo"Abramo, L. Raul"https://zbmath.org/authors/?q=ai:abramo.l-raul-w"Sodré, Laerte jun."https://zbmath.org/authors/?q=ai:sodre.laerte-junSummary: We investigate the turnaround radius in the spherical collapse model, both in General Relativity and in modified gravity, in particular \(f(R)\) scenarios. The phases of spherical collapse are marked by the non-linear density contrast in the instant of turnaround \(\delta_t\), and by the linear density contrast in the moment of collapse, \(\delta_c\). We find that the effective mass of the extra scalar degree of freedom which arises in modified gravity models has an impact on \(\delta_t\) of up to \(\sim 16\)\%, and that \(\delta_c\) can increase by \(\sim 2.3\)\%, for structures with mass of \(\simeq 10^{13}\,h^{-1} M_\odot\) at \(z \simeq 0\). We also compute the turnaround radius, \(R_t\), which in modified gravity models can increase by up to \(\sim 6\)\%.Neutron stars in the braneworld within the Eddington-inspired Born-Infeld gravityhttps://zbmath.org/1527.850102024-02-28T19:32:02.718555Z"Prasetyo, I."https://zbmath.org/authors/?q=ai:prasetyo.ilham"Husin, I."https://zbmath.org/authors/?q=ai:husin.i"Qauli, A. I."https://zbmath.org/authors/?q=ai:qauli.a-i"Ramadhan, H. S."https://zbmath.org/authors/?q=ai:ramadhan.handhika-s"Sulaksono, A."https://zbmath.org/authors/?q=ai:sulaksono.aSummary: We propose the disappearance of ``the hyperon puzzle'' in neutron star (NS) by invoking two new-physics prescriptions: modified gravity theory and braneworld scenario. By assuming that NS lives on a 3-brane within a \(5d\) empty AdS bulk, gravitationally governed by Eddington-inspired Born-Infeld (EiBI) theory, the field equations can be effectively cast into the usual Einstein's with ``apparent'' anisotropic energy-momentum tensor. Solving the corresponding brane-TOV equations numerically, we study its mass-radius relation. It is known that the appearance of finite brane tension \(\lambda\) reduces the compactness of the star. The compatibility of the braneworld results with observational constraints of NS mass and radius can be restored in our model by varying the EiBI's coupling constant, \(\kappa\). We found that within the astrophysically-accepted range of parameters (\(0< \kappa<6\times 10^6 \mathrm{m}^2\) and \(\lambda \gg 1\;\mathrm{MeV}^4\)) the NS can have mass \(\sim 2.1\;\mathrm{M}_\odot\) and radius \(\sim 10\) km.