Recent zbMATH articles in MSC 83C15https://zbmath.org/atom/cc/83C152021-06-15T18:09:00+00:00WerkzeugBlack rings in large \(D\) membrane paradigm at the first order.https://zbmath.org/1460.830172021-06-15T18:09:00+00:00"Mandlik, Mangesh"https://zbmath.org/authors/?q=ai:mandlik.mangeshSummary: Black rings are the black objects found in \(D\) spacetime dimensional gravity when \( D \geq 5 \). These have event horizon topology \(S^{D - 3} \times S^1\). In this work the solutions of the large \(D\) membrane paradigm dual to stationary black rings in Einstein-Maxwell theory with or without cosmological constant are studied. It is shown that the first order membrane equations can only admit static asymptotically flat black rings, and the equilibrium angular velocity for the asymptotically AdS black rings at large \(D\) was obtained. The thermodynamic and dynamic stability of the asymptotically flat black ring solutions is studied. The apparent shortcomings of some of these results are argued to be curable within the large \(D\) membrane paradigm framework.
Reviewer: Reviewer (Berlin)The Einstein-Rosen bridge and the Einstein-Podolsky-Rosen argument: singularities and separability.https://zbmath.org/1460.830112021-06-15T18:09:00+00:00"Weinstein, Galina"https://zbmath.org/authors/?q=ai:weinstein.galinaSummary: In 1935 Einstein pursued two main paths separately: the Einstein-Rosen (ER) bridge theory [\textit{A. Einstein} and \textit{N. Rosen}, Phys. Rev., II. Ser. 48, 73--77 (1935; Zbl 0012.13401)] and the Einstein-Podolsky-Rosen (EPR) argument [\textit{A. Einstein} et al., Phys. Rev., II. Ser. 47, 777--780 (1935; Zbl 0012.04201)]. In this paper, I deal with the static two-particle problem in general relativity and relationship of this problem with the two projects on which Einstein worked in parallel. I discuss two questions: What was the possible role played by the static two-body problem in the rise and fall of the ER bridge theory? What was the possible role played by the static two-body problem in Einstein's formulations of the EPR argument? Finally, I also briefly discuss a possible link between Einstein's work on EPR and the ER bridge.
For the entire collection see [Zbl 1457.83003].
Reviewer: Reviewer (Berlin)Neutral signature gauged supergravity solutions.https://zbmath.org/1460.830152021-06-15T18:09:00+00:00"Gutowski, J."https://zbmath.org/authors/?q=ai:gutowski.jan-b"Sabra, W. A."https://zbmath.org/authors/?q=ai:sabra.wafic-aSummary: We classify all supersymmetric solutions of minimal \(D = 4\) gauged supergravity with (2) signature and a positive cosmological constant which admit exactly one Killing spinor. This classification produces a geometric structure which is more general than that found for previous classifications of \(N = 2\) supersymmetric solutions of this theory. We illustrate how the \(N = 2\) solutions which consist of a fibration over a 3-dimensional Lorentzian Gauduchon-Tod base space can be written in terms of this more generic geometric structure.
Reviewer: Reviewer (Berlin)Resonant frequencies of a massless scalar field in the canonical acoustic black hole spacetime.https://zbmath.org/1460.830552021-06-15T18:09:00+00:00"Vieira, H. S."https://zbmath.org/authors/?q=ai:vieira.h-s"Bezerra, V. B."https://zbmath.org/authors/?q=ai:bezerra.valdir-bSummary: In this work we consider the exact solution of the Klein-Gordon equation describing a massless scalar field in the spacetime of a four dimensional canonical acoustic black hole, which is given in terms of the general Heun function, to investigate the interesting phenomena related to the resonant frequencies.
Reviewer: Reviewer (Berlin)On the nature of cosmic strings in black hole spacetimes.https://zbmath.org/1460.831002021-06-15T18:09:00+00:00"Kofroň, David"https://zbmath.org/authors/?q=ai:kofron.davidStarting from the ``Bonnor rocket'' type solutions [\textit{W. B. Bonnor}, Classical Quantum Gravity 13, No. 2, 277--282 (1996; Zbl 0845.53061)], through a limiting procedure, a metric is constructed that corresponds to a Schwarzschild black hole with a conical defect representing a cosmic string. It is shown that the solution has a novel stress energy source that implies a momentum flux through the string leading to the acceleration of the black hole.
Reviewer: Jorge Pullin (Baton Rouge)Thermodynamically stable asymptotically flat hairy black holes with a dilaton potential: the general case.https://zbmath.org/1460.830842021-06-15T18:09:00+00:00"Astefanesei, Dumitru"https://zbmath.org/authors/?q=ai:astefanesei.dumitru"Blázquez-Salcedo, Jose Luis"https://zbmath.org/authors/?q=ai:blazquez-salcedo.jose-luis"Gómez, Francisco"https://zbmath.org/authors/?q=ai:gomez.francisco-j"Rojas, Raúl"https://zbmath.org/authors/?q=ai:rojas.raul.1Summary: We extend the analysis, initiated in [\textit{D. Astefanesei} et al., J. High Energy Phys. 2019, No. 3, Paper No. 205, 43 p. (2019; Zbl 1414.83081)], of the thermodynamic stability of four-dimensional asymptotically flat hairy black holes by considering a general class of exact solutions in Einstein-Maxwell-dilaton theory with a non-trivial dilaton potential. We find that, regardless of the values of the parameters of the theory, there always exists a sub-class of hairy black holes that are thermodynamically stable and have the extremal limit well defined. This generic feature that makes the equilibrium configurations locally stable should be related to the properties of the dilaton potential that is decaying towards the spatial infinity, but behaves as a box close to the horizon. We prove that these thermodynamically stable solutions are also dynamically stable under spherically symmetric perturbations.
Reviewer: Reviewer (Berlin)On the nonexistence of a vacuum black lens.https://zbmath.org/1460.830472021-06-15T18:09:00+00:00"Lucietti, James"https://zbmath.org/authors/?q=ai:lucietti.james"Tomlinson, Fred"https://zbmath.org/authors/?q=ai:tomlinson.fredSummary: We demonstrate that five-dimensional, asymptotically flat, stationary and bi-axisymmetric, vacuum black holes with lens space \(L(n,1) \) topology, possessing the simplest rod structure, do not exist. In particular, we show that the general solution on the axes and horizon, which we recently constructed by exploiting the integrability of this system, must suffer from a conical singularity on the inner axis component. We give a proof of this for two distinct singly spinning configurations and numerical evidence for the generic doubly spinning solution.
Reviewer: Reviewer (Berlin)Anisotropic compact stellar model of embedding class-I satisfying Karmarkar's condition in Vaidya and Tikekar spheroidal geometry.https://zbmath.org/1460.850012021-06-15T18:09:00+00:00"Das, Shyam"https://zbmath.org/authors/?q=ai:das.shyam"Sharma, Ranjan"https://zbmath.org/authors/?q=ai:sharma.ranjan"Chakraborty, Koushik"https://zbmath.org/authors/?q=ai:chakraborty.koushik"Baskey, Lipi"https://zbmath.org/authors/?q=ai:baskey.lipiSummary: We present a class of solutions for a spherically symmetric anisotropic matter distribution in Vaidya and Tikekar spheroidal geometry. Making use of the \textit{P. C. Vaidya} and \textit{R. Tikekar} (VT) metric ansatz [``Exact relativistic model for a superdense star'', J. Astrophys. Astron. 3, No. 3, 325--334 (1982; \url{doi:10.1007/BF02714870}] for one of the metric functions \(g_{rr}\), we obtain the unknown metric function \(g_{tt}\) by utilizing the Karmakar's embedding condition which makes the master equation tractable. The model parameters are fixed by utilizing the matching conditions of the interior spacetime and the exterior Schwarzschild solution at the boundary of the star where the radial pressure vanishes. The closed-form interior solution of the Einstein field equations thus obtained is shown to be capable of describing ultra-compact stellar objects where anisotropy might develop. The current estimated masses and radii of some other pulsars are utilized to show that the developed model meets all the requirements of a realistic star. The stability of the model is analyzed. The dependence of the curvature parameter \(K\) of the VT model, which characterizes a departure from homogeneous spherical distribution, is also investigated.
Reviewer: Reviewer (Berlin)Positive periodic solutions of Friedmann's equation for the acceleration of the cosmological scale factor.https://zbmath.org/1460.830142021-06-15T18:09:00+00:00"Belley, Jean-Marc"https://zbmath.org/authors/?q=ai:belley.jean-marcSummary: Given \(T > 0\), \(\Lambda \in \mathbb{R}\), \(k \in \{- 1, 0, 1 \}\) and \(T\)-periodic function \(p\) of bounded variation on \([0, T]\), we obtain conditions that guarantee the existence of a strictly positive \(T\)-periodic almost everywhere solution of Friedmann's nonlinear equation \(a'' = (\Lambda - 8 \pi p) a / 2 -( a^{\prime^2} + k) / 2 a\) with singularity. Both \(a\) and \(a^\prime\) will be absolutely continuous and \(a''\) Lebesgue integrable on \([0, T]\). This makes \(a\) a scale factor for an FRW cosmology with pressure \(p\), cosmological constant \(\Lambda\) and energy density equal to \(3( a^{\prime^2} + k) / 8 \pi a^2 - \Lambda / 8 \pi \). By way of Picard iterates, \(a\) and \(a^{\prime}\) can be obtained numerically.
Reviewer: Reviewer (Berlin)A new parametric class of solutions of a charged anisotropic compact star via Bardeen exterior geometry.https://zbmath.org/1460.830162021-06-15T18:09:00+00:00"Gedela, Satyanarayana"https://zbmath.org/authors/?q=ai:gedela.satyanarayana"Pant, Neeraj"https://zbmath.org/authors/?q=ai:pant.neeraj"Upreti, Jaya"https://zbmath.org/authors/?q=ai:upreti.jaya"Pant, R. P."https://zbmath.org/authors/?q=ai:pant.r-p|pant.rajendra-prasadSummary: In this paper, we provide a new parametric class of solutions to Einstein-Maxwell field equations to study the relativistic structure of a compact star via embedding class I condition. The interior of the star is delineated by Karmarkar condition and at the boundary of the star, we match the class of solutions with Bardeen and Reissner-Nordstrom exterior spacetimes. We assume one of the metric potentials as \(e^{\lambda (r)}=1+ c_1 r^2 \mathrm{csc}^n(1+ c_2 r^2)\) to obtain other metric potential. Subsequently, we solve Maxwell field equations. We verify and compare all the thermodynamic properties like matter density, anisotropy, radial and tangential pressures, compactification factor, energy conditions, and stability conditions, namely, adiabatic index, balancing forces via modified TOV equations, Harrision-Zeldovich criteria, casualty condition, Herrera cracking condition, etc., of our class of charged solutions. All the physical and stability conditions are with the viable trend throughout the interior of the stellar object. For a suitable range of values of \(n\) and parameters, it is depicted from this study that the present class of charged solutions yields effective results to obtain realistic and viable modeling of the neutron star in EXO 1785-248 in both the Bardeen and Reissner-Nordstrom exterior spacetimes.
Reviewer: Reviewer (Berlin)New \(\mathrm{AdS}_4\) vacua in dyonic ISO(7) gauged supergravity.https://zbmath.org/1460.831092021-06-15T18:09:00+00:00"Bobev, Nikolay"https://zbmath.org/authors/?q=ai:bobev.nokolai"Fischbacher, Thomas"https://zbmath.org/authors/?q=ai:fischbacher.thomas"Gautason, Fridrik Freyr"https://zbmath.org/authors/?q=ai:gautason.fridrik-freyr"Pilch, Krzysztof"https://zbmath.org/authors/?q=ai:pilch.krzysztofSummary: We identify 219 \( \mathrm{AdS}_4\) solutions in four-dimensional dyonically gauged ISO(7) \( \mathcal{N} = 8\) supergravity and present some of their properties. One of the new solutions preserves \(\mathcal{N} = 1\) supersymmetry and provides a rare explicit example of an \(\mathrm{AdS}_4\) vacuum dual to a 3d SCFT with no continuous global symmetry. There are also two new non-supersymmetric solutions for which all 70 scalar fields in the supergravity theory have masses above the BF bound. All of these \(\mathrm{AdS}_4\) solutions can be uplifted to massive type IIA supergravity. Motivated by this we present the low lying operator spectra of the dual 3d CFTs for all known supersymmetric \(\mathrm{AdS}_4\) solutions in the theory and organize them into superconformal multiplets.
Reviewer: Reviewer (Berlin)Thermodynamic criticality of d-dimensional charged AdS black holes surrounded by quintessence with a cloud of strings background.https://zbmath.org/1460.830392021-06-15T18:09:00+00:00"Chabab, M."https://zbmath.org/authors/?q=ai:chabab.mohamed"Iraoui, Samir"https://zbmath.org/authors/?q=ai:iraoui.samirSummary: We focus on the study of exact solutions corresponding to charged AdS black holes surrounded by quintessence with a cloud of strings present in higher dimensional spacetime. We then investigate its corresponding thermodynamic criticality in the extended phase space and show that the spacetime dimension has no effect on the existence of small/large phase transition for such black holes. The heat capacity is evaluated and the geothermodynamics of \textit{H. Quevedo} [J. Math. Phys. 48, No. 1, 013506, 14 p. (2007; Zbl 1121.80011)] analyzed for different spacetime dimensions with the cloud of strings and quintessence parameters. We calculate the critical exponents describing the behavior of relevant thermodynamic quantities near the critical point. Finally, we also discuss the uncharged case, show how it is sensitive to the quintessence and strings cloud parameters, and when the thermodynamic behavior of the uncharged black holes is similar to Van der Waals fluid.
Reviewer: Reviewer (Berlin)Universal black holes.https://zbmath.org/1460.830462021-06-15T18:09:00+00:00"Hervik, Sigbjørn"https://zbmath.org/authors/?q=ai:hervik.sigbjorn"Ortaggio, Marcello"https://zbmath.org/authors/?q=ai:ortaggio.marcelloThe (\(n+2\))-dimensional Schwarzschild spacetime has the Lorentzian metric \( g= - f(t) dt^2 + \frac{1}{f(t)} dr^2 + r^2 h \), where \(h\) is the metric of the \(n\)-dimensional sphere.
In the paper under review, the authors consider a family of Schwarzschild-like metrics, by multiplying the previous metric on the (\(t,r\))-plane with a (positive) conformal factor function \(e^{a(r)}\), and by relaxing the hypothesis on \(h\), which is a Riemannian metric on an \(n\)-dimensional ``universal'' space. The main purpose of the paper is to obtain sufficient conditions on the metric \(h\) and on the functions \(f\) and \(a\), which enable the new Lorentzian metric to be consistently employed in theories of gravity modelling a static vacuum black hole. Examples are constructed in concrete contexts as solutions in particular theories, such as Gauss-Bonnet, quadratic, F(R) and F(Lovelock) gravity, and certain conformal gravities.
Reviewer: Gabriel Teodor Pripoae (Bucureşti)