Recent zbMATH articles in MSC 83https://zbmath.org/atom/cc/832022-11-17T18:59:28.764376ZWerkzeugCategory theory and the foundations of classical space-time theorieshttps://zbmath.org/1496.180092022-11-17T18:59:28.764376Z"Weatherall, James Owen"https://zbmath.org/authors/?q=ai:weatherall.james-owenThe entire volume has been reviewed in [Zbl 1491.03006].
For the entire collection see [Zbl 1491.03006].The self-interacting Dirac fields in FLRW spacetimehttps://zbmath.org/1496.353362022-11-17T18:59:28.764376Z"Galstian, Anahit"https://zbmath.org/authors/?q=ai:galstian.anahit"Yagdjian, Karen"https://zbmath.org/authors/?q=ai:yagdjian.karenSummary: We prove the existence of global in time solution with the small initial data for the semilinear equation of the spin-\(\frac{1}{2}\) particles in the Friedmann-Lemaître-Robertson-Walker spacetime. Moreover, we also prove that if the initial function satisfies the Lochak-Majorana condition, then the global solution exists for arbitrary large initial value. The solution scatters to free solution for large time. The mass term is assumed to be complex-valued. The conditions on the imaginary part of mass are discussed by proving nonexistence of the global solutions if certain relation between scale function and the mass are fulfilled.Conformal scattering theory for the Dirac equation on Kerr spacetimehttps://zbmath.org/1496.353392022-11-17T18:59:28.764376Z"Truong Xuan Pham"https://zbmath.org/authors/?q=ai:truong-xuan-pham.Summary: We establish the construction of a conformal scattering theory of the spin-1/2 massless Dirac equation on the Kerr spacetime by using the conformal geometric method and a pointwise logarithmic decay estimate for the massless Dirac field. In particular, our construction is valid on the exterior domains of Kerr black hole spacetimes in the full sub-extremal range \(|a|<M\).Space Cauchy problem with curvature \(L^2\) in general relativityhttps://zbmath.org/1496.353822022-11-17T18:59:28.764376Z"Graf, Olivier"https://zbmath.org/authors/?q=ai:graf.olivierSummary: The present article is a summary of the papers [\textit{S. Czimek} and \textit{O. Graf}, ``The canonical foliation on null hypersurfaces in low regularity'', Preprint, \url{arXiv:1909.07345}; ``The spacelike-characteristic Cauchy problem of general relativity in low regularity'', Preprint, \url{arXiv:1909.07355}] which establish a bounded \(L^2\) curvature theorem for the spacelike-characteristic Cauchy problem of general relativity. More precisely, we obtain a lower bound on the time of existence of classical solutions to the spacelike-characteristic Cauchy problem for Einstein equations in vacuum, depending only on the \(L^2\) curvature fluxes through the initial spacelike and initial characteristic hypersurfaces and on suitable additional low regularity assumptions.Harmonic functions and the mass of 3-dimensional asymptotically flat Riemannian manifoldshttps://zbmath.org/1496.530482022-11-17T18:59:28.764376Z"Bray, Hubert L."https://zbmath.org/authors/?q=ai:bray.hubert-l"Kazaras, Demetre P."https://zbmath.org/authors/?q=ai:kazaras.demetre-p"Khuri, Marcus A."https://zbmath.org/authors/?q=ai:khuri.marcus-a"Stern, Daniel L."https://zbmath.org/authors/?q=ai:stern.daniel-lSummary: An explicit lower bound for the mass of an asymptotically flat Riemannian 3-manifold is given in terms of linear growth harmonic functions and scalar curvature. As a consequence, a new proof of the positive mass theorem is achieved in dimension three. The proof has parallels with both the Schoen-Yau minimal hypersurface technique and Witten's spinorial approach. In particular, the role of harmonic spinors and the Lichnerowicz formula in Witten's argument is replaced by that of harmonic functions and a formula introduced by the fourth named author in recent work, while the level sets of harmonic functions take on a role similar to that of the Schoen-Yau minimal hypersurfaces.Quintessential effects on quasiperiodic oscillations in \(4D\) Einstein-Gauss-Bonnet gravityhttps://zbmath.org/1496.531062022-11-17T18:59:28.764376Z"Rayimbaev, Javlon"https://zbmath.org/authors/?q=ai:rayimbaev.javlon"Tadjimuratov, Pulat"https://zbmath.org/authors/?q=ai:tadjimuratov.pulat"Ahmedov, Bobomurat"https://zbmath.org/authors/?q=ai:ahmedov.bobomurat-j"Palvanov, Satimbay"https://zbmath.org/authors/?q=ai:palvanov.satimbayThe authors focused their attention on discussing the dynamics of test particles in a quintessential black hole space-time with the help of Einstein-Gauss-Bonnet theory of gravity. On this purpose, firstly, they analyzed the main features of space-time geometry and possible values for the coupling and quintessential parameters. Subsequently, they investigated (i) the case when the quintessential black hole event horizon lies at 2M, (ii) scalar invariants of the selected spacetime model, (iii) the effects of the quintessential and the Gauss-Bonnet parameters on the effective potential for radial motion, specific energy and angular momentum of the particles corresponding to their circular orbits, (iv) the effects of the parameters on innermost stable circular orbit radius, (v) the relations between the quintessential and the Gauss-Bonnet parameters providing 6M innermost stable circular orbit radius and (vi) the cases with fundamental frequencies such as the Keplerian and harmonic oscillations.
Reviewer: Mustafa Salti (Mersin)Projective points over matrices and their separability propertieshttps://zbmath.org/1496.540072022-11-17T18:59:28.764376Z"Agnew, Alfonso F."https://zbmath.org/authors/?q=ai:agnew.alfonso-f"Rathbun, Matt"https://zbmath.org/authors/?q=ai:rathbun.matt"Terry, William"https://zbmath.org/authors/?q=ai:terry.williamThe authors focus their work on topological quotients of real and complex matrices, by various subgroups, and they study their separation properties, as this finds an immediate application to twistor spaces in mathematical physics. As a main conclusion, the authors find that as the group one quotients by gets smaller, the separability properties of the quotient improve. The authors then pose a number of topological questions. For example, the quotient by the general linear group is compact, but the others are not; is there a ground of a further topological study, apart from the separation properties? What about the homotopy or homology properties?
Reviewer: Kyriakos Papadopoulos (Madīnat al-Kuwait)A variational principle for Kaluza-Klein types theorieshttps://zbmath.org/1496.580032022-11-17T18:59:28.764376Z"Hélein, Frédéric"https://zbmath.org/authors/?q=ai:helein.fredericSummary: For any positive integer \(n\) and any Lie group \(\mathfrak{G}\), given a definite symmetric bilinear form on \(\mathbb{R}^n\) and an Ad-invariant scalar product on the Lie algebra of \(\mathfrak{G} \), we construct a variational problem on fields defined on an arbitrary oriented \((n + \dim\mathfrak{G})\)-dimensional manifold \(\mathcal{Y}\). We show that, if \(\mathfrak{G}\) is compact and simply connected, any global solution of the Euler-Lagrange equations leads, through a spontaneous symmetry breaking, to identify \(\mathcal{Y}\) with the total space of a principal bundle over an n-dimensional manifold \(\mathcal{X} \). Moreover \(\mathcal{X}\) is then endowed with a (pseudo-)Riemannian metric and a connection which are solutions of the Einstein-Yang-Mills system of equations with a cosmological constant.An introduction to quantum fluidshttps://zbmath.org/1496.760052022-11-17T18:59:28.764376Z"Dinh, Phuong Mai"https://zbmath.org/authors/?q=ai:dinh.phuong-mai"Navarro, Jesús"https://zbmath.org/authors/?q=ai:navarro.jesus-gerardo"Suraud, Éric"https://zbmath.org/authors/?q=ai:suraud.ericPublisher's description: What do atomic nuclei, neutron stars, a domestic power supply, and the stunning colors of stained glass in cathedrals all have in common? The answer lies in the unifying concept of quantum fluids, which allows us to understand the behavior and properties of these different systems in simple terms. This book reveals how quantum mechanics, usually considered as restricted to the invisible microscopic world, in fact plays a crucial role at all scales of the universe. The purpose of the book is to introduce the reader to the fascinating and multifaceted world of quantum fluids, which covers different systems at different scales in the physical world.
The first part of the book discusses the notion of phases (solid, liquid, gas), presents basic aspects of the structure of matter and quantum mechanics, and includes some elements of statistical mechanics. The second part provides a description of the major quantum liquids, starting with the paramount case of electron fluids and their many applications in everyday life, followed by liquid helium and atomic nuclei. The authors go on to explore matter at very high densities, covering nuclear matter and compact stars, and the behavior of matter at extremely low temperatures, with the fascinating `superphases' of superconductivity and superfluidity.
The topic of quantum fluids has multidisciplinary applications and this book will appeal to students and researchers in physics, chemistry, astrophysics, engineering and materials science.Physics from symmetryhttps://zbmath.org/1496.810112022-11-17T18:59:28.764376Z"Schwichtenberg, Jakob"https://zbmath.org/authors/?q=ai:schwichtenberg.jakobPublisher's description: This is a textbook that derives the fundamental theories of physics from symmetry.
It starts by introducing, in a completely self-contained way, all mathematical tools needed to use symmetry ideas in physics. Thereafter, these tools are put into action and by using symmetry constraints, the fundamental equations of Quantum Mechanics, Quantum Field Theory, Electromagnetism, and Classical Mechanics are derived.
As a result, the reader is able to understand the basic assumptions behind, and the connections between the modern theories of physics. The book concludes with first applications of the previously derived equations.
Thanks to the input of readers from around the world, this second edition has been purged of typographical errors and also contains several revised sections with improved explanations.
See the review of the first edition in [Zbl 1330.81005].Simultaneous vs. non-simultaneous measurements in quantum and classical mechanicshttps://zbmath.org/1496.810262022-11-17T18:59:28.764376Z"Chudak, N. O."https://zbmath.org/authors/?q=ai:chudak.n-o"Potiienko, O. S."https://zbmath.org/authors/?q=ai:potiienko.o-s"Sharph, I. V."https://zbmath.org/authors/?q=ai:sharph.i-vSummary: In a traditional implementation of the relativity principles, different observers consider \textit{the same} events and relate their space-time coordinates through the Lorentz transformation. In this paper we consider the problems where it is impossible to use the non-simultaneous measurements in any inertial reference frame. In such case different observers have to use \textit{different} sets of events, the space-time coordinates of which are impossible to relate through Lorentz transform. Therefore we suggest another way of implementing the relativity principles, and discuss some of its consequences and prospects.Construction of quantum target space from world-sheet states using quantum state tomographyhttps://zbmath.org/1496.810332022-11-17T18:59:28.764376Z"Wani, Salman Sajad"https://zbmath.org/authors/?q=ai:wani.salman-sajad"Shabir, Arshid"https://zbmath.org/authors/?q=ai:shabir.arshid"Hassan, Junaid Ul"https://zbmath.org/authors/?q=ai:hassan.junaid-ul"Kannan, S."https://zbmath.org/authors/?q=ai:kannan.senthamarai|kannan.sriraman|kannan.srinathan|kannan.sriram|kannan.siddarth|kannan.sreeram"Patel, Hrishikesh"https://zbmath.org/authors/?q=ai:patel.hrishikesh"Sudheesh, C."https://zbmath.org/authors/?q=ai:sudheesh.c"Faizal, Mir"https://zbmath.org/authors/?q=ai:faizal.mirSummary: In this paper, we will construct the quantum states of target space coordinates from world-sheet states, using quantum state tomography. To perform quantum state tomography of an open string, we will construct suitable quadrature operators. We do this by first defining the quadrature operators in world-sheet, and then using them to construct the quantum target space quadrature operators for an open string. We will connect the quantum target space to classical geometry using coherent string states. We will be using a novel construction based on a string displacement operator to construct these coherent states. The coherent states of the world-sheet will also be used to construct the coherent states in target space.Optical effects of domain wallshttps://zbmath.org/1496.810682022-11-17T18:59:28.764376Z"Khoze, Valentin V."https://zbmath.org/authors/?q=ai:khoze.valentin-v"Milne, Daniel L."https://zbmath.org/authors/?q=ai:milne.daniel-lSummary: Domain walls arise in theories where there is spontaneous symmetry breaking of a discrete symmetry such as \(\mathbb{Z}_N\) and are a feature of many BSM models. In this work we consider the possibility of detecting domain walls through their optical effects and specify three different methods of coupling domain walls to the photon. We consider the effects of these couplings in the context of gravitational wave detectors, such as LIGO, and examine the sensitivity of these experiments to domain wall effects. In cases where gravitational wave detectors are not sensitive we examine our results in the context of axion experiments and show how effects of passing domain walls can be detected at interferometers searching for an axion signal.The noncommutative space of light-like worldlineshttps://zbmath.org/1496.810692022-11-17T18:59:28.764376Z"Ballesteros, Angel"https://zbmath.org/authors/?q=ai:ballesteros.angel"Gutierrez-Sagredo, Ivan"https://zbmath.org/authors/?q=ai:gutierrez-sagredo.ivan"Herranz, Francisco J."https://zbmath.org/authors/?q=ai:herranz.francisco-joseSummary: The noncommutative space of light-like worldlines that is covariant under the light-like (or null-plane) \(\kappa\)-deformation of the (3+1) Poincaré group is fully constructed as the quantization of the corresponding Poisson homogeneous space of null geodesics. This new noncommutative space of geodesics is five-dimensional, and turns out to be defined as a quadratic algebra that can be mapped to a non-central extension of the direct sum of two Heisenberg-Weyl algebras whose noncommutative parameter is just the Planck scale parameter \(\kappa^{-1}\). Moreover, it is shown that the usual time-like \(\kappa\)-deformation of the Poincaré group does not allow the construction of the Poisson homogeneous space of light-like worldlines. Therefore, the most natural choice in order to model the propagation of massless particles on a quantum Minkowski spacetime seems to be provided by the light-like \(\kappa\)-deformation.Erratum to: ``Superstring backgrounds in string geometry''https://zbmath.org/1496.810812022-11-17T18:59:28.764376Z"Honda, Masaki"https://zbmath.org/authors/?q=ai:honda.masaki"Sato, Matsuo"https://zbmath.org/authors/?q=ai:sato.matsuo"Tohshima, Taiki"https://zbmath.org/authors/?q=ai:tohshima.taikiFrom the text: In [\textit{M. Honda} et al., Adv. High Energy Phys. 2021, Article ID 9993903, 7 p. (2021; Zbl 1473.81137)], a minor discrepancy between the PDF and HTML versions of the article was identified. This was caused by an error during the conversion of the LaTex file during the production of the article and the PDF version has therefore been updated to correct these errors.Transport properties of a 3-dimensional holographic effective theory with gauge-axion couplinghttps://zbmath.org/1496.810872022-11-17T18:59:28.764376Z"Li, Yi-Lin"https://zbmath.org/authors/?q=ai:li.yilin"Wang, Xi-Jing"https://zbmath.org/authors/?q=ai:wang.xi-jing"Fu, Guoyang"https://zbmath.org/authors/?q=ai:fu.guoyang"Wu, Jian-Pin"https://zbmath.org/authors/?q=ai:wu.jian-pinSummary: In this paper, we implement a 3-dimensional holographic effective theory with gauge-axion coupling. The analytical black hole solution is worked out. We investigate the Direct current (DC) thermoelectric conductivities. A novel property is that DC electric conductivity for vanishing gauge-axion coupling is temperature dependent. It is different from that of 4-dimensional axion model whose DC electric conductivity is temperature independent. In addition, the gauge-axion coupling induces a metal insulator transition (MIT) at zero temperature. The properties of other DC thermoelectric conductivities are also discussed. Moreover we find that the Wiedemann-Franz (WF) law is violated in our model.Global aspects of moduli spaces of 2d SCFTshttps://zbmath.org/1496.810882022-11-17T18:59:28.764376Z"Donagi, Ron"https://zbmath.org/authors/?q=ai:donagi.ron-y"Macerato, Mark"https://zbmath.org/authors/?q=ai:macerato.mark"Sharpe, Eric"https://zbmath.org/authors/?q=ai:sharpe.eric-rSummary: The Bagger-Witten line bundle is a line bundle over moduli spaces of two-dimensional SCFTs, related to the Hodge line bundle of holomorphic top-forms on Calabi-Yau manifolds. It has recently been a subject of a number of conjectures, but concrete examples have proven elusive. In this paper we propose a new, intrinsically geometric definition of the Bagger-Witten line bundle, whose restriction to the moduli spaces of complex structures of Calabi-Yau manifolds we explicitly compute in some concrete examples. We also conjecture a new criterion for UV completion of four-dimensional supergravity theories in terms of properties of the Bagger-Witten line bundle.Very special linear gravity: a gauge-invariant graviton masshttps://zbmath.org/1496.830012022-11-17T18:59:28.764376Z"Alfaro, Jorge"https://zbmath.org/authors/?q=ai:alfaro.jorge"Santoni, Alessandro"https://zbmath.org/authors/?q=ai:santoni.alessandroSummary: Linearized gravity in the Very Special Relativity (VSR) framework is considered. We prove that this theory allows for a non-zero graviton mass \(m_g\) without breaking gauge invariance nor modifying the relativistic dispersion relation. We find the analytic solution for the new equations of motion in our gauge choice, verifying as expected the existence of only two physical degrees of freedom. Finally, through the geodesic deviation equation, we confront some results for classic gravitational waves (GW) with the VSR ones: we see that the ratios between VSR effects and classical ones are proportional to \((m_g/E)^2\), \(E\) being the energy of a graviton in the GW. For GW detectable by the interferometers LIGO and VIRGO this ratio is at most \(10^{-20}\). However, for GW in the lower frequency range of future detectors, like LISA, the ratio increases significantly to \(10^{-10}\), that combined with the anisotropic nature of VSR phenomena may lead to observable effects.Special cosmological models derived from the semiclassical Einstein equation on flat FLRW space-timeshttps://zbmath.org/1496.830022022-11-17T18:59:28.764376Z"Gottschalk, Hanno"https://zbmath.org/authors/?q=ai:gottschalk.hanno"Rothe, Nicolai R."https://zbmath.org/authors/?q=ai:rothe.nicolai-r"Siemssen, Daniel"https://zbmath.org/authors/?q=ai:siemssen.danielThe Einstein equations and multipole moments at null infinityhttps://zbmath.org/1496.830032022-11-17T18:59:28.764376Z"Tafel, J."https://zbmath.org/authors/?q=ai:tafel.jacekJacobi-Maupertuis Randers-Finsler metric for curved spaces and the gravitational magnetoelectric effecthttps://zbmath.org/1496.830042022-11-17T18:59:28.764376Z"Chanda, Sumanto"https://zbmath.org/authors/?q=ai:chanda.sumanto"Gibbons, G. W."https://zbmath.org/authors/?q=ai:gibbons.gary-william"Guha, Partha"https://zbmath.org/authors/?q=ai:guha.partha"Maraner, Paolo"https://zbmath.org/authors/?q=ai:maraner.paolo"Werner, Marcus C."https://zbmath.org/authors/?q=ai:werner.marcus-cSummary: In this paper, we return to the subject of Jacobi metrics for timelike and null geodesics in stationary spacetimes, correcting some previous misconceptions. We show that not only null geodesics but also timelike geodesics are governed by a Jacobi-Maupertuis type variational principle and a Randers-Finsler metric for which we give explicit formulas. The cases of the Taub-NUT and Kerr spacetimes are discussed in detail. Finally, we show how our Jacobi-Maupertuis Randers-Finsler metric may be expressed in terms of the effective medium describing the behavior of Maxwell's equations in the curved spacetime. In particular, we see in very concrete terms how the gravitational electric permittivity, magnetic permeability, and magnetoelectric susceptibility enter the Jacobi-Maupertuis Randers-Finsler function.\par{\copyright 2019 American Institute of Physics}Classical double copy at null infinityhttps://zbmath.org/1496.830052022-11-17T18:59:28.764376Z"Adamo, Tim"https://zbmath.org/authors/?q=ai:adamo.tim"Kol, Uri"https://zbmath.org/authors/?q=ai:kol.uriMöbius mirrorshttps://zbmath.org/1496.830062022-11-17T18:59:28.764376Z"Good, Michael R. R."https://zbmath.org/authors/?q=ai:good.michael-r-r"Linder, Eric V."https://zbmath.org/authors/?q=ai:linder.eric-vOn almost Ehlers-Geren-Sachs theoremshttps://zbmath.org/1496.830072022-11-17T18:59:28.764376Z"Lee, Ho"https://zbmath.org/authors/?q=ai:lee.ho"Nungesser, Ernesto"https://zbmath.org/authors/?q=ai:nungesser.ernesto"Stalker, John"https://zbmath.org/authors/?q=ai:stalker.john-gViscous absorption of ultra-high-frequency gravitonshttps://zbmath.org/1496.830082022-11-17T18:59:28.764376Z"Giovannini, Massimo"https://zbmath.org/authors/?q=ai:giovannini.massimoSummary: The high-frequency gravitons can be absorbed by the first and second viscosities of the post-inflationary plasma as the corresponding wavelengths reenter the Hubble radius prior to big-bang nucleosynthesis. When the total sound speed of the medium is stiffer than radiation the rate of expansion still exceeds the shear rate but the bulk viscosity is not negligible. Depending on the value of the entropy density at the end of inflation the spectral energy density of the relic gravitons gets modified in comparison with the inviscid result when the frequency ranges between the kHz band and the GHz region. In the nHz domain the spectrum inherits a known suppression due to neutrino free-streaming but also a marginal spike potentially caused by a sudden outbreak of the bulk viscosity around the quark-hadron phase transition, as suggested by the hadron spectra produced in the collisions of heavy ions.Displacement-noise-free neutron interferometer for gravitational wave detection using a single Mach-Zehnder configurationhttps://zbmath.org/1496.830092022-11-17T18:59:28.764376Z"Iwaguchi, Shoki"https://zbmath.org/authors/?q=ai:iwaguchi.shoki"Nishizawa, Atsushi"https://zbmath.org/authors/?q=ai:nishizawa.atsushi-j"Chen, Yanbei"https://zbmath.org/authors/?q=ai:chen.yanbei"Kawasaki, Yuki"https://zbmath.org/authors/?q=ai:kawasaki.yuki"Kitaguchi, Masaaki"https://zbmath.org/authors/?q=ai:kitaguchi.masaaki"Morimoto, Taigen"https://zbmath.org/authors/?q=ai:morimoto.taigen"Ishikawa, Tomohiro"https://zbmath.org/authors/?q=ai:ishikawa.tomohiro"Wu, Bin"https://zbmath.org/authors/?q=ai:wu.bin"Watanabe, Izumi"https://zbmath.org/authors/?q=ai:watanabe.izumi"Shimizu, Ryuma"https://zbmath.org/authors/?q=ai:shimizu.ryuma"Shimizu, Hirohiko"https://zbmath.org/authors/?q=ai:shimizu.hirohiko-m"Michimura, Yuta"https://zbmath.org/authors/?q=ai:michimura.yuta"Kawamura, Seiji"https://zbmath.org/authors/?q=ai:kawamura.seijiSummary: The improvement of sensitivity to gravitational waves (GWs) at lower frequencies is still challenging on account of displacement noise. One of the solutions is the neutron displacement-noise-free interferometer (DFI). We focus on a simplification of the detector configuration by taking advantage of the ability to adjust the neutron speed depending on the configuration. The new configuration consists of two beamsplitters and two mirrors, which constitute a single Mach-Zehnder interferometer (MZI). It is simpler than the configuration with two MZIs in previous research. All displacement noise of mirrors and beamsplitters can be canceled in the frequency domain. This cancellation can be explained intuitively using a phasor diagram.Conformally flat pseudoprojective symmetric spacetimes in \(f(R, \mathcal{G})\) gravityhttps://zbmath.org/1496.830102022-11-17T18:59:28.764376Z"De, Uday Chand"https://zbmath.org/authors/?q=ai:de.uday-chand"Shenawy, Sameh"https://zbmath.org/authors/?q=ai:shenawy.sameh"Syied, Abdallah Abdelhameed"https://zbmath.org/authors/?q=ai:syied.abdallah-abdelhameed"Turki, Nasser Bin"https://zbmath.org/authors/?q=ai:turki.nasser-bin(no abstract)Darboux vector in four-dimensional space-timehttps://zbmath.org/1496.830112022-11-17T18:59:28.764376Z"Hu, Na"https://zbmath.org/authors/?q=ai:hu.na"Zhang, Tingting"https://zbmath.org/authors/?q=ai:zhang.tingting"Jiang, Yang"https://zbmath.org/authors/?q=ai:jiang.yang(no abstract)Non-isothermal squeeze film damping in the test of gravitational inverse-square lawhttps://zbmath.org/1496.830122022-11-17T18:59:28.764376Z"Ke, Jun"https://zbmath.org/authors/?q=ai:ke.jun"Luo, Jie"https://zbmath.org/authors/?q=ai:luo.jie"Tan, Yu-Jie"https://zbmath.org/authors/?q=ai:tan.yujie"Liu, Zhe"https://zbmath.org/authors/?q=ai:liu.zhe"Shao, Cheng-Gang"https://zbmath.org/authors/?q=ai:shao.chenggang"Yang, Shan-Qing"https://zbmath.org/authors/?q=ai:yang.shan-qingShadows in conformally related gravity theorieshttps://zbmath.org/1496.830132022-11-17T18:59:28.764376Z"Pal, Kunal"https://zbmath.org/authors/?q=ai:pal.kunal"Pal, Kuntal"https://zbmath.org/authors/?q=ai:pal.kuntal"Shaikh, Rajibul"https://zbmath.org/authors/?q=ai:shaikh.rajibul"Sarkar, Tapobrata"https://zbmath.org/authors/?q=ai:sarkar.tapobrataSummary: Null geodesics are invariant under a conformal transformation, and thus it might seem natural to assume that the observables corresponding to the shadow of a space-time are also conformally invariant. Here, we argue instead, that since the Arnowitt-Deser-Misner mass and the active gravitational mass of an asymptotically flat space-time are not, in general, invariant under such conformal transformations, the shadow radius for photon motion in a space-time would be quantitatively different, when viewed from two different conformally related frames, although the expression for the shadow radius is similar. We then use this fact to propose a novel method to constrain the relevant parameters in a gravity theory conformally related to general relativity. As examples of our method, we constrain the parameter space in Brans-Dicke theory, and a class of brane-world gravity models, by using the recent observational data of M\(87^\ast\) by the Event Horizon Telescope.Generalized geodesic deviation in de Sitter spacetimehttps://zbmath.org/1496.830142022-11-17T18:59:28.764376Z"Waldstein, Isaac Raj"https://zbmath.org/authors/?q=ai:waldstein.isaac-raj"Brown, J. David"https://zbmath.org/authors/?q=ai:brown.j-davidQuantum black hole-white hole entangled stateshttps://zbmath.org/1496.830152022-11-17T18:59:28.764376Z"Jalalzadeh, S."https://zbmath.org/authors/?q=ai:jalalzadeh.shahramSummary: We investigate the quantum deformation of the Wheeler-DeWitt equation of a Schwarzchild black hole. Specifically, the quantum deformed black hole is a quantized model constructed from the quantum Heisenberg-Weyl \(U_q(h_4)\) group. We show that the event horizon area and the mass are quantized, degenerate, and bounded. The degeneracy of states indicates entangled quantum black hole/white hole states. Accordingly, quantum deformation provides a new framework to examine Einstein-Rosen wormhole solutions. Besides, we obtain the mass, the temperature, and the entropy of the \(q\)-deformed quantum Schwarzschild black hole. We find an upper bound on the mass of a black hole/white hole pair. Also, at the quantum deformation level, the entropy of the black hole contains three parts: the usual Bekenstein-Hawking entropy, the logarithmic term, and a Cube of usual black hole entropy.Quantum speed limit and stability of coherent states in quantum gravityhttps://zbmath.org/1496.830162022-11-17T18:59:28.764376Z"Liegener, Klaus"https://zbmath.org/authors/?q=ai:liegener.klaus"Rudnicki, Łukasz"https://zbmath.org/authors/?q=ai:rudnicki.lukaszLocal conformal instability and local non-collapsing in the Ricci flow of quantum spacetimehttps://zbmath.org/1496.830172022-11-17T18:59:28.764376Z"Luo, M. J."https://zbmath.org/authors/?q=ai:luo.meiju|luo.meijin|luo.ming-jianSummary: It is known that the conformal instability or bottomless problem rises in the path integral method in quantizing the general relativity. Does quantum spacetime itself really suffer from such conformal instability? If so, does the conformal instability cause the collapse of local spacetime region or even collapse the whole spacetime? The problems are studied in the framework of the Quantum Spacetime Reference Frame (QSRF) and induced spacetime Ricci flow. We find that if the lowest eigenvalue of an operator, associated with the F-functional in a local compact (closed and bounded) region, is positive, the local region is conformally unstable and will tend to volume-shrinking and curvature-pinching along the Ricci flow-time t; if the eigenvalue is negative or zero, the local region is conformally stable up to a trivial rescaling. However, the local non-collapsing theorem in the Ricci flow proved by Perelman ensures that the instability will not cause the local compact spacetime region collapse into nothing. The total effective action is also proved positive defined and bounded from below keeping the whole spacetime conformally stable, which can be considered as a generalization of the classical positive mass theorem of gravitation to the quantum level.Two-component scalar and fermionic dark matter candidates in a generic \(U(1)_X\) modelhttps://zbmath.org/1496.830182022-11-17T18:59:28.764376Z"Das, Arindam"https://zbmath.org/authors/?q=ai:das.arindam"Gola, Shivam"https://zbmath.org/authors/?q=ai:gola.shivam"Mandal, Sanjoy"https://zbmath.org/authors/?q=ai:mandal.sanjoy"Sinha, Nita"https://zbmath.org/authors/?q=ai:sinha.nitaSummary: We consider a \(U(1)_X \otimes \mathbb{Z}_2 \otimes \mathbb{Z}_2^\prime\) extension of the Standard Model (SM), where the \(U(1)_X\) charge of an SM field is given by a linear combination of its hypercharge and \(B-L\) number. Apart from the SM particle content, the model contains three right-handed neutrinos (RHNs) \(N_R^i\) and two scalars \(\Phi\), \(\chi\), all singlets under the SM gauge group but charged under \(U(1)_X\) gauge group. Two of these additional fields, fermion \(N_R^3\) is odd under \(\mathbb{Z}_2\) and scalar \(\chi\) is odd under \(\mathbb{Z}_2^\prime\) symmetry. Thus both \(\chi\) and \(N_R^3\) contribute to the observed dark matter relic density, leading to two-component dark matter candidates. We study in detail its dark matter properties such as relic density and direct detection taking into account the constraints coming from collider studies. We find that in our model, there can be possible annihilation of one Dark Matter (DM) into the other, which may potentially alter the relic density in a significant way.Scotogenic \(A_5 \rightarrow A_4\) Dirac neutrinos with freeze-in dark matterhttps://zbmath.org/1496.830192022-11-17T18:59:28.764376Z"Ma, Ernest"https://zbmath.org/authors/?q=ai:ma.ernestSummary: Radiative Dirac neutrino masses and their mixing are linked to dark matter through the non-Abelian discrete symmetry \(A_5\) of the 4-dimensional pentatope, softly broken to \(A_4\) of the 3-dimensional tetrahedron. This unifying understanding of neutrino family structure from dark matter is made possible through the interplay of gauge symmetry, renormalizable Lagrangian field theory, and softly broken discrete symmetries. Dark neutral fermions are produced through Higgs decay.An effective model for the quantum Schwarzschild black holehttps://zbmath.org/1496.830202022-11-17T18:59:28.764376Z"Alonso-Bardaji, Asier"https://zbmath.org/authors/?q=ai:alonso-bardaji.asier"Brizuela, David"https://zbmath.org/authors/?q=ai:brizuela.david"Vera, Raül"https://zbmath.org/authors/?q=ai:vera.raulSummary: We present an effective theory to describe the quantization of spherically symmetric vacuum motivated by loop quantum gravity. We include anomaly-free holonomy corrections through a canonical transformation and a linear combination of constraints of general relativity, such that the modified constraint algebra closes. The system is then provided with a fully covariant and unambiguous geometric description, independent of the gauge choice on the phase space. The resulting spacetime corresponds to a singularity-free (black-hole/white-hole) interior and two asymptotically flat exterior regions of equal mass. The interior region contains a minimal smooth spacelike surface that replaces the Schwarzschild singularity. We find the global causal structure and the maximal analytical extension. Both Minkowski and Schwarzschild spacetimes are directly recovered as particular limits of the model.Applications of the close-limit approximation: horizonless compact objects and scalar fieldshttps://zbmath.org/1496.830212022-11-17T18:59:28.764376Z"Annulli, Lorenzo"https://zbmath.org/authors/?q=ai:annulli.lorenzo"Cardoso, Vitor"https://zbmath.org/authors/?q=ai:cardoso.vitor"Gualtieri, Leonardo"https://zbmath.org/authors/?q=ai:gualtieri.leonardoTesting gravity with black hole shadow subringshttps://zbmath.org/1496.830222022-11-17T18:59:28.764376Z"Ayzenberg, Dimitry"https://zbmath.org/authors/?q=ai:ayzenberg.dimitryOptical and thermodynamic behaviors of Ayón-Beato-García black holes for 4D Einstein Gauss-Bonnet gravityhttps://zbmath.org/1496.830232022-11-17T18:59:28.764376Z"Belhaj, Adil"https://zbmath.org/authors/?q=ai:belhaj.adil"Sekhmani, Yassine"https://zbmath.org/authors/?q=ai:sekhmani.yassineSummary: We investigate a family of four dimensional \((4D)\) Ayón-Beato-García (ABG) black holes in Einstein Gauss-Bonnet (EGB) gravity. We approach and examine the associated thermodynamic and the optical aspects by varying the involved parameters. We first compute and analyze the corresponding thermodynamic quantities. Among others, we inspect the global and the local stability behaviors. Then, we study the optical behaviors. Using Hamilton-Jacobi method, we study the shadow geometrical configurations in terms of one dimensional real closed curves. Using Gauss-Bonnet theorem, we calculate and examine the deflection angle of light rays by such black holes. In specific regions of a reduced moduli space obtained by fixing the mass and varying the remaining parameters, the present work recovers certain previous findings. Finally, we provide a possible speculative connection with observations from Event Horizon Telescope by imposing certain constraints on the involved b parameters in the light of the M\(87^\ast\) image.Quantum corrections enhance chaos: study of particle motion near a generalized Schwarzschild black holehttps://zbmath.org/1496.830242022-11-17T18:59:28.764376Z"Bera, Avijit"https://zbmath.org/authors/?q=ai:bera.avijit"Dalui, Surojit"https://zbmath.org/authors/?q=ai:dalui.surojit"Ghosh, Subir"https://zbmath.org/authors/?q=ai:ghosh.subir.1|ghosh.subir|ghosh.subir-kumar"Vagenas, Elias C."https://zbmath.org/authors/?q=ai:vagenas.elias-cSummary: The paper is devoted to a detailed study of the effects of quantum corrections on the chaotic behaviour in the dynamics of a (massless) probe particle near the horizon of a generalized Schwarzschild black hole. Two possible origins inducing the modification of black hole metric are considered separately; the noncommutative geometry inspired metric (suggested by Nicolini, Smailagic and Spallucci) and the metric with quantum field theoretic corrections (derived by Donoghue). Our results clearly show that in both cases, the metric extensions favour chaotic behaviour, namely chaos is attained for relatively lower particle energy. This is demonstrated numerically by exhibiting the breaking of the KAM tori in Poincaré sections of particle trajectories and also via explicit computation of the (positive) Lyapunov exponents of the trajectories.Aspects of three-dimensional higher curvatures gravitieshttps://zbmath.org/1496.830252022-11-17T18:59:28.764376Z"Bueno, Pablo"https://zbmath.org/authors/?q=ai:bueno.pablo"Cano, Pablo A."https://zbmath.org/authors/?q=ai:cano.pablo-a"Llorens, Quim"https://zbmath.org/authors/?q=ai:llorens.quim"Moreno, Javier"https://zbmath.org/authors/?q=ai:moreno.javier"van der Velde, Guido"https://zbmath.org/authors/?q=ai:van-der-velde.guidoTopological confinement in Skyrme holographyhttps://zbmath.org/1496.830262022-11-17T18:59:28.764376Z"Cartwright, Casey"https://zbmath.org/authors/?q=ai:cartwright.casey"Harms, Benjamin"https://zbmath.org/authors/?q=ai:harms.benjamin-c"Kaminski, Matthias"https://zbmath.org/authors/?q=ai:kaminski.matthias"Thomale, Ronny"https://zbmath.org/authors/?q=ai:thomale.ronnyHow not to extract information from black holes: cosmic censorship as a guiding principlehttps://zbmath.org/1496.830272022-11-17T18:59:28.764376Z"Di Gennaro, Sofia"https://zbmath.org/authors/?q=ai:di-gennaro.sofia"Ong, Yen Chin"https://zbmath.org/authors/?q=ai:ong.yen-chinSummary: Black holes in general relativity are commonly believed to evolve towards a Schwarzschild state as they gradually lose angular momentum and electrical charge under Hawking evaporation. However, when Kim and Wen applied quantum information theory to Hawking evaporation and argued that Hawking particles with maximum mutual information could dominate the emission process, they found that charged black holes tend towards extremality. In view of some evidence pointing towards extremal black holes being effectively singular, this would violate the cosmic censorship conjecture. Nevertheless, since the Kim-Wen model is too simplistic (e.g. it assumes a continuous spectrum of particles with arbitrary charge-to-mass ratio), one might hope that a more realistic model could avoid this problem. In this work, we show that having only a finite species of charged particles would actually worsen the situation, with some end states becoming a naked singularity. With this model as an example, we emphasize the need to study whether charged black holes can violate cosmic censorship under a given model of Hawking evaporation.AdS-dS stationary rotating black hole exact solution within Einstein-nonlinear electrodynamicshttps://zbmath.org/1496.830282022-11-17T18:59:28.764376Z"García-Díaz, Alberto A."https://zbmath.org/authors/?q=ai:garcia-diaz.alberto-aSummary: In this report the exact rotating charged black hole solution to the Einstein-nonlinear electrodynamics theory with a cosmological constant is presented. This black hole is equipped with mass, rotation parameter, electric and magnetic charges, cosmological constant \(\Lambda\), and three parameters due to the nonlinear electrodynamics: \(\beta\) is associated to the potential vectors \(A_\mu\) and \(^\star P_\mu\), and two constants, \(F_0\) and \(G_0\), due to the presence of the invariants \(F\) and \(G\) in the Lagrangian \(L(F(x^\mu),G(x^\mu))\). This solution is of Petrov type D, characterized by the Weyl tensor eigenvalue \(\Psi_2\), the traceless Ricci tensor eigenvalue \(S=2\Phi_{(11)}\), and the scalar curvature \(R\); it allows for event horizons, exhibits a ring singularity and fulfils the energy conditions. Its Maxwell limit is the de Sitter-Anti-de Sitter-Kerr-Newman black hole solution.Effect of the magnetic charge on weak deflection angle and greybody bound of the black hole in Einstein-Gauss-Bonnet gravityhttps://zbmath.org/1496.830292022-11-17T18:59:28.764376Z"Javed, Wajiha"https://zbmath.org/authors/?q=ai:javed.wajiha"Aqib, Muhammad"https://zbmath.org/authors/?q=ai:aqib.muhammad"Övgün, Ali"https://zbmath.org/authors/?q=ai:ovgun.aliSummary: The objective of this paper is to analyze the weak deflection angle of Einstein-Gauss-Bonnet gravity in the presence of plasma medium. To attain our results, we implement the Gibbons and Werner approach and use the Gauss-Bonnet theorem to Einstein gravity to acquire the resulting deflection angle of photon's ray in the weak field limit. Moreover, we illustrate the behavior of plasma medium and non-plasma mediums on the deflection of photon's ray in the framework of Einstein-Gauss-Bonnet gravity. Similarly, we observe the graphical influences of deflection angle on Einstein-Gauss-Bonnet gravity with the consideration of both plasma and non-plasma mediums. Later, we observe the rigorous bounds phenomenon of the greybody factor in contact with Einstein-Gauss-Bonnet gravity and calculate the outcomes, analyze graphically for specific values of parameters.On superstatistics and black hole quasinormal modeshttps://zbmath.org/1496.830302022-11-17T18:59:28.764376Z"Martínez-Merino, A."https://zbmath.org/authors/?q=ai:martinez-merino.aldo-a"Sabido, M."https://zbmath.org/authors/?q=ai:sabido.miguelSummary: It is known that using Boltzmann-Gibbs statistics, Bekenstein-Hawking entropy \(S_{HB}\), and the quasinormal modes of black holes, one finds that the lowest value of spin is \(j_{min} = 1\). In this paper, we determine \(j_{min}\), using non-extensive entropies that depend only on the probability (known as Obregon's entropies and have been derived from superstatistics). We also calculate \(j_{min}\) for a set of non-extensive entropies that have free parameters and are written in terms of \(S_{BH}\). We find that \(j_{min}\) depends on the area and the non-extensive parameter.
For the non-extensive entropies that only depend on the probability, we find that the modification is only present for micro black holes. For classical black holes the results are the same as for the Boltzmann-Gibbs statistics.The Penrose property with a cosmological constanthttps://zbmath.org/1496.830312022-11-17T18:59:28.764376Z"Cameron, Peter"https://zbmath.org/authors/?q=ai:cameron.peter-jThe accidental flatness constraint does not mean a wrong classical limithttps://zbmath.org/1496.830322022-11-17T18:59:28.764376Z"Engle, Jonathan"https://zbmath.org/authors/?q=ai:engle.jonathan-s"Rovelli, Carlo"https://zbmath.org/authors/?q=ai:rovelli.carloLaplacian on fuzzy de Sitter spacehttps://zbmath.org/1496.830332022-11-17T18:59:28.764376Z"Brkić, Bojana"https://zbmath.org/authors/?q=ai:brkic.bojana"Burić, Maja"https://zbmath.org/authors/?q=ai:buric.maja"Latas, Duško"https://zbmath.org/authors/?q=ai:latas.duskoThe topological RN-AdS black holes cannot be overcharged by the new version of gedanken experimenthttps://zbmath.org/1496.830342022-11-17T18:59:28.764376Z"Huang, Yong-Ming"https://zbmath.org/authors/?q=ai:huang.yongming"Tian, Yu"https://zbmath.org/authors/?q=ai:tian.yu"Wu, Xiao-Ning"https://zbmath.org/authors/?q=ai:wu.xiaoning"Zhang, Hongbao"https://zbmath.org/authors/?q=ai:zhang.hongbaoSummary: In this paper, we test the weak cosmic censorship conjecture (WCCC) for \(n\geq4\) dimensional nearly extremal RN-AdS black holes with non-trivial topologies, namely plane and hyperbola, using the new version of gedanken experiment proposed by Sorce and Wald. Provided that the non-electromagnetic part of the stress tensor of matter fields satisfies the null energy condition and the linear stability condition holds, we find that the black holes cannot be overcharged under the second-order perturbation approximation, which includes the self-force and finite-size effects. As a result, we conclude that the violation of Hubeny type never occurs and the WCCC holds for the topological RN-AdS black hole.Uniformly accelerated Brownian oscillator in (2+1)D: temperature-dependent dissipation and frequency shifthttps://zbmath.org/1496.830352022-11-17T18:59:28.764376Z"Moustos, Dimitris"https://zbmath.org/authors/?q=ai:moustos.dimitrisSummary: We consider an Unruh-DeWitt detector modeled as a harmonic oscillator that is coupled to a massless quantum scalar field in the (2+1)-dimensional Minkowski spacetime. We treat the detector as an open quantum system and employ a quantum Langevin equation to describe its time evolution, with the field, which is characterized by a frequency-independent spectral density, acting as a stochastic force. We investigate a point-like detector moving with constant acceleration through the Minkowski vacuum and an inertial one immersed in a thermal reservoir at the Unruh temperature, exploring the implications of the well-known non-equivalence between the two cases on their dynamics. We find that both the accelerated detector's dissipation rate and the shift of its frequency caused by the coupling to the field bath depend on the acceleration temperature. Interestingly enough this is not only in contrast to the case of inertial motion in a heat bath but also to any analogous quantum Brownian motion model in open systems, where dissipation and frequency shifts are not known to exhibit temperature dependencies. Nonetheless, we show that the fluctuating-dissipation theorem still holds for the detector-field system and in the weak-coupling limit an accelerated detector is driven at late times to a thermal equilibrium state at the Unruh temperature.Stability analysis of anisotropic Bianchi type-I cosmological model in teleparallel gravityhttps://zbmath.org/1496.830362022-11-17T18:59:28.764376Z"Koussour, M."https://zbmath.org/authors/?q=ai:koussour.m"Bennai, M."https://zbmath.org/authors/?q=ai:bennai.mohamedElectromagnetic effects on dynamics of string fluid and information paradox in rainbow gravityhttps://zbmath.org/1496.830372022-11-17T18:59:28.764376Z"Sheikh, Umber"https://zbmath.org/authors/?q=ai:sheikh.umber"Arshad, Sana"https://zbmath.org/authors/?q=ai:arshad.sanaSummary: This work is devoted to studying the effects of electric field intensity on collapsing anisotropic string fluid in Rainbow gravity. The Einstein field equations are modified and solved for the spherical symmetric spacetime. The physical parameters of fluid including energy density, pressure and string tension are obtained. Moreover, the time and radius of formation of the apparent horizon are estimated. All these quantities depend on the fluid's electric intensity. The graphical analysis of the physical existence of dynamical quantities depending on the energy of the probing particle is presented. It is found that the presence of an electric field decreases the mass density and increases fluid's pressure. The electric field increases the time and radius of apparent horizon formation resulting in slowing down the collapsing process.Interaction of inhomogeneous axions with magnetic fields in the early universehttps://zbmath.org/1496.830382022-11-17T18:59:28.764376Z"Dvornikov, Maxim"https://zbmath.org/authors/?q=ai:dvornikov.maximSummary: We study the system of interacting axions and magnetic fields in the early universe after the quantum chromodynamics phase transition, when axions acquire masses. Both axions and magnetic fields are supposed to be spatially inhomogeneous. We derive the equations for the spatial spectra of these fields, which depend on conformal time. In case of the magnetic field, we deal with the spectra of the energy density and the magnetic helicity density. The evolution equations are obtained in the closed form within the mean field approximation. We choose the parameters of the system and the initial condition which correspond to realistic primordial magnetic fields and axions. The system of equations for the spectra is solved numerically. We compare the cases of inhomogeneous and homogeneous axions. The evolution of the magnetic field in these cases is different only within small time intervals. Generally, magnetic fields are driven mainly by the magnetic diffusion. We find that the magnetic field instability takes place for the amplified initial wavefunction of the homogeneous axion. This instability is suppressed if we account for the inhomogeneity of the axion.Natural chain inflationhttps://zbmath.org/1496.830392022-11-17T18:59:28.764376Z"Freese, Katherine"https://zbmath.org/authors/?q=ai:freese.katherine"Litsa, Aliki"https://zbmath.org/authors/?q=ai:litsa.aliki"Winkler, Martin Wolfgang"https://zbmath.org/authors/?q=ai:winkler.martin-wolfgangSummary: In Chain Inflation the universe tunnels along a series of false vacua of ever-decreasing energy. The main goal of this paper is to embed Chain Inflation in high energy fundamental physics. We begin by illustrating a simple effective formalism for calculating Cosmic Microwave Background (CMB) observables in Chain Inflation. Density perturbations seeding the anisotropies emerge from the probabilistic nature of tunneling (rather than from quantum fluctuations of the inflation). To obtain the correct normalization of the scalar power spectrum and the scalar spectral index, we find an upper limit on the scale of inflation at horizon crossing of CMB scales, \(V_\ast^{1/4} < 10^{12}\) GeV. We then provide an explicit realization of chain inflation, in which the inflaton is identified with an axion in supergravity. The axion enjoys a perturbative shift symmetry which is broken to a discrete remnant by instantons. The model, which we dub `natural chain inflation' satisfies all cosmological constraints and can be embedded into a standard \(\Lambda\)CDM cosmology. Our work provides a major step towards the ultraviolet completion of chain inflation in string theory.Emergence of space and expansion of universehttps://zbmath.org/1496.830402022-11-17T18:59:28.764376Z"V T, Hassan Basari"https://zbmath.org/authors/?q=ai:v-t.hassan-basari"Krishna, P. B."https://zbmath.org/authors/?q=ai:krishna.p-b"K. V, Priyesh"https://zbmath.org/authors/?q=ai:k-v.priyesh"Mathew, Titus K."https://zbmath.org/authors/?q=ai:mathew.titus-kOn maximal acceleration, strings with dynamical tension, and Rindler worldsheetshttps://zbmath.org/1496.830412022-11-17T18:59:28.764376Z"Castro Perelman, Carlos"https://zbmath.org/authors/?q=ai:castro-perelman.carlosSummary: Starting with a different action and following a different procedure than the construction of strings with dynamical tensions described by \textit{E. I. Guendelman} [``Implications of the spectrum of dynamically generated string tension theories'', Int. J. Mod. Phys. D 30, No.14, Article ID 2142028, 9 p. (2021; \url{doi:10.1142/S0218271821420281})], a variational procedure of our action leads to a coupled nonlinear system of \(D + 4\) partial differential equations for the \(D\) string coordinates \(X^\mu\) and the \textit{quartet} of scalar fields \(\varphi^1\), \(\varphi^2\), \(\phi\), \(T\), including the dilaton \(\phi(\sigma)\) and the tension \(T(\sigma)\) field. Trivial solutions to this system of complicated equations lead to a constant tension and to the standard string equations of motion. One of the most relevant features of our findings is that the Weyl invariance of the traditional Polyakov string is traded for the invariance under area-preserving diffeomorphisms. The final section is devoted to the physics of maximal proper forces (acceleration), minimal length within the context of Born's Reciprocal Relativity theory [\textit{C. Castro Perelman}, ``Is dark matter and black hole cosmology an effect of Born's reciprocal relativity theory?'', Can. J. Phys. 97, No. 2, 198--209 (2019; \url{doi.org/10.1139/cjp-2018-0097})] and to the Rindler world sheet description of accelerated \textit{open} and \textit{closed} strings from a very different approach and perspective than the one undertaken by [\textit{A. Bagchi} et al., ``A Rindler road to Carrollian worldsheets'', Preprint, \url{arXiv:2111.01172}; \textit{A. Bagchi}, \textit{A. Banerjee} and \textit{S. Chakrabotty}, ``Rindler physics on the string worldsheet'', Phys. Rev. Lett. 126, No. 3, Article ID 031601, 6 p. (2021; \url{doi:10.1103/PhysRevLett.126.031601})].Tensionless strings and Killing(-Yano) tensorshttps://zbmath.org/1496.830422022-11-17T18:59:28.764376Z"Lindström, Ulf"https://zbmath.org/authors/?q=ai:lindstrom.ulf"Sarıoğlu, Özgür"https://zbmath.org/authors/?q=ai:sarioglu.ozgurSummary: We construct invariants for bosonic and spinning tensionless (null) strings in backgrounds that carry Killing tensors or Killing-Yano tensors of mixed type. This is facilitated by the close relation of these strings to point particles. We apply the construction to the Minkowski and to the Kerr-Newman backgrounds.Asymmetrically twisted stringshttps://zbmath.org/1496.830432022-11-17T18:59:28.764376Z"Lipinski Jusinskas, Renann"https://zbmath.org/authors/?q=ai:lipinski-jusinskas.renannSummary: In this letter a new class of twisted strings is presented, with an asymmetry between the holomorphic and antiholomorphic sectors parametrized by an integer \(N\). Their physical content is given by the massless resonances of the closed string plus the mass-level \(N\) spectrum of the open string. The appeal of this model is the singling out of the (higher spin) massive levels of string theory together with their self/gauge/gravity interactions. Motivated by the original tree level Kawai-Lewellen-Tye relation for closed strings, its asymmetrically twisted version at four points is conjectured and shown to naturally interpolate with conventional and twisted strings. The resulting four-point amplitudes have a generalized Virasoro-Shapiro dressing factor.Traversable wormhole on the brane with non-exotic matter: a broader viewhttps://zbmath.org/1496.830442022-11-17T18:59:28.764376Z"Sengupta, Rikpratik"https://zbmath.org/authors/?q=ai:sengupta.rikpratik"Ghosh, Shounak"https://zbmath.org/authors/?q=ai:ghosh.shounak"Kalam, Mehedi"https://zbmath.org/authors/?q=ai:kalam.mehedi"Ray, Saibal"https://zbmath.org/authors/?q=ai:ray.saibalFlow equations in arbitrary signaturehttps://zbmath.org/1496.830452022-11-17T18:59:28.764376Z"Sabra, W. A."https://zbmath.org/authors/?q=ai:sabra.wafic-aSummary: We discuss general bosonic configurations of four-dimensional \(N = 2\) supergravity coupled to vector multiplets in \((t, s)\) space-time. The supergravity theories with Euclidean and neutral signature are described by the so-called para-special Kähler geometry. For extremal solutions, we derive in a unified fashion, using the equations of motion, the flow equations for all space-time signatures. Demanding that the solutions with neutral and Euclidean signatures admit unbroken supersymmetry, we derive the constraints, known as the stabilisation equations, on the para-covariantly holomorphic sections expressed in terms of the adapted coordinates. The stabilisation equations expressed in terms of the para-complex sections imply generalised flow equations in terms of para-complex central charge. For Euclidean and neutral signature, it is demonstrated that solutions for either signs of gauge kinetic terms are mapped into each other via field redefinitions.Density perturbation and cosmological evolution in the presence of magnetic field in \(f(R)\) gravity modelshttps://zbmath.org/1496.830462022-11-17T18:59:28.764376Z"Chakraborty, Samarjit"https://zbmath.org/authors/?q=ai:chakraborty.samarjit"Guha, Sarbari"https://zbmath.org/authors/?q=ai:guha.sarbariSummary: In this paper, we have investigated the density perturbations and cosmological evolution in the FLRW universe in the presence of a cosmic magnetic field, which may be assumed to mimic primordial magnetic fields. Such magnetic fields have sufficient strength to influence galaxy formation and cluster dynamics, thereby leaving an imprint on the CMB anisotropies. We have considered the FLRW universe as a representative of the isotropic cosmological model in the \(1+3\) covariant formalism for \(f(R)\) gravity. The propagation equations have been determined and analyzed, where we have assumed that the magnetic field is aligned uniformly along the \(x\)-direction, resulting in a diagonal shear tensor. Subsequently, the density perturbation evolution equations have been studied, and the results have been interpreted. We have also indicated how these results change in the general relativistic case and briefly mentioned the expected change in higher-order gravity theories.Cosmological viability of a double field unified model from warm inflationhttps://zbmath.org/1496.830472022-11-17T18:59:28.764376Z"D'Agostino, Rocco"https://zbmath.org/authors/?q=ai:dagostino.rocco"Luongo, Orlando"https://zbmath.org/authors/?q=ai:luongo.orlandoSummary: In this paper, we investigate the cosmological viability of a double scalar field model motivated by warm inflation. To this end, we first set up the theoretical framework in which dark energy, dark matter and inflation are accounted for in a triple unification scheme. We then compute the overall dynamics of the model, analyzing the physical role of coupling parameters. Focussing on the late-time evolution, we test the model against current data. Specifically, using the low-redshift Pantheon Supernovae Ia and Hubble cosmic chronometers measurements, we perform a Bayesian analysis through the Monte Carlo Markov Chains method of integration on the free parameters of the model. We find that the mean values of the free parameters constrained by observations lie within suitable theoretical ranges, and the evolution of the scalar fields provides a good resemblance to the features of the dark sector of the universe. Such behaviour is confirmed by the outcomes of widely adopted selection criteria, suggesting a statistical evidence comparable to that of the standard \(\Lambda\)CDM cosmology. We finally discuss the presence of large uncertainties over the free parameters of the model and we debate about fine-tuning issues related to the coupling constants.Observational constraints on inflection point quintessence with a cubic potentialhttps://zbmath.org/1496.830482022-11-17T18:59:28.764376Z"Storm, S. David"https://zbmath.org/authors/?q=ai:storm.s-david"Scherrer, Robert J."https://zbmath.org/authors/?q=ai:scherrer.robert-jSummary: We examine the simplest inflection point quintessence model, with a potential given by \(V(\phi) = V_0 + V_3\phi^3\). This model can produce either asymptotic de Sitter expansion or transient acceleration, and we show that it does not correspond to either pure freezing or thawing behavior. We derive observational constraints on the initial value of the scalar field, \(\phi_i\), and \(V_3/V_0\) and find that small values of either \(\phi_i\) or \(V_3/V_0\) are favored. While most of the observationally-allowed parameter space yields asymptotic de Sitter evolution, there is a small region, corresponding to large \(V_3/V_0\) and small \(\phi_i\), for which the current accelerated expansion is transient. The latter behavior is potentially consistent with a cyclic universe.Vanishing Poynting observers and electromagnetic field classification in Kerr and Kerr-Newman spacetimeshttps://zbmath.org/1496.830492022-11-17T18:59:28.764376Z"Vargas-Rodríguez, H."https://zbmath.org/authors/?q=ai:vargas-rodriguez.hector"Rosu, H. C."https://zbmath.org/authors/?q=ai:rosu.haret-c"Medina-Guevara, M. G."https://zbmath.org/authors/?q=ai:medina-guevara.maria-g"Gallegos, A."https://zbmath.org/authors/?q=ai:gallegos.armando"Muñiz-Torres, M. A."https://zbmath.org/authors/?q=ai:muniz-torres.m-aSummary: We consider electromagnetic fields having an angular momentum density in a locally nonrotating reference frame in Schwarzschild, Kerr, and Kerr-Newman spacetimes. The nature of such fields is assessed with two families of observers, the locally nonrotating ones and those of vanishing Poynting flux. The velocity fields of the vanishing-Poynting observers in the locally nonrotating reference frames are determined using the \(3+1\) decomposition formalism. From a methodological point of view and considering a classification of the electromagnetic field based on its invariants, it is convenient to separate the consideration of the vanishing-Poynting observers into two cases corresponding to the pure and nonpure fields; additionally, if there are regions where the field rotates with the speed of light (light surfaces), it becomes necessary to split these observers into two subfamilies. We present several examples of relevance in astrophysics and general relativity, such as pure rotating dipolar-like magnetic fields and the electromagnetic field of the Kerr-Newman solution. For the latter example, we see that vanishing-Poynting observers also measure a vanishing super-Poynting vector, confirming recent results in the literature. Finally, for all nonnull electromagnetic fields, we present the 4-velocity fields of vanishing Poynting observers in an arbitrary spacetime.New light rings from multiple critical curves as observational signatures of black hole mimickershttps://zbmath.org/1496.850032022-11-17T18:59:28.764376Z"Olmo, Gonzalo J."https://zbmath.org/authors/?q=ai:olmo.gonzalo-j"Rubiera-Garcia, Diego"https://zbmath.org/authors/?q=ai:rubiera-garcia.diego"Sáez-Chillón Gómez, Diego"https://zbmath.org/authors/?q=ai:saez-chillon-gomez.diegoSummary: We argue that the appearance of additional light rings in a shadow observation -- beyond the infinite sequence of exponentially demagnified self-similar rings foreseen in the Kerr solution - would make a compelling case for the existence of black hole mimickers having multiple critical curves. We support this claim by discussing three different scenarios of spherically symmetric wormhole geometries having two such critical curves, and explicitly work out the optical appearance of one such object when surrounded by an optically and geometrically thin accretion disk.Structure of magnetized strange quark star in perturbative QCDhttps://zbmath.org/1496.850042022-11-17T18:59:28.764376Z"Sedaghat, J."https://zbmath.org/authors/?q=ai:sedaghat.j"Zebarjad, S. M."https://zbmath.org/authors/?q=ai:zebarjad.s-mohammad|zebarjad.seyed-mostafa"Bordbar, G. H."https://zbmath.org/authors/?q=ai:bordbar.g-h"Eslam Panah, B."https://zbmath.org/authors/?q=ai:eslam-panah.bSummary: We have performed the leading order perturbative calculation to obtain the equation of state (EoS) of the strange quark matter (SQM) at zero temperature under the magnetic field \(B = 10^{18}G\). The SQM comprises two massless quark flavors (up and down) and one massive quark flavor (strange). Consequently, we have used the obtained EoS to calculate the maximum gravitational mass and the corresponding radius of the magnetized strange quark star (SQS). We have employed two approaches, including the regular perturbation theory (\textbf{RPT}) and the background perturbation theory (\textbf{BPT}). In \textbf{RPT} the infrared (IR) freezing effect of the coupling constant has not been accounted for, while this effect has been included in \textbf{BPT}. We have obtained the value of the maximum gravitational mass to be more than three times the solar mass. The validity of isotropic structure calculations for SQS has also been investigated. Our results show that the threshold magnetic field from which an anisotropic approach begins to be significant lies in the interval \(2 \times 10^{18}G < B < 3 \times 10^{18}G\). Furthermore, we have computed the redshift, compactness and Buchdahl-Bondi bound of the SQS to show that this compact object cannot be a black hole.