Recent zbMATH articles in MSC 83https://www.zbmath.org/atom/cc/832022-05-16T20:40:13.078697ZWerkzeugConformal scattering and the Goursat problem for Dirac fields in the interior of charged spherically symmetric black holeshttps://www.zbmath.org/1483.351712022-05-16T20:40:13.078697Z"Mokdad, Mokdad"https://www.zbmath.org/authors/?q=ai:mokdad.mokdadA density theorem for asymptotically hyperbolic initial datahttps://www.zbmath.org/1483.352612022-05-16T20:40:13.078697Z"Dahl, Mattias"https://www.zbmath.org/authors/?q=ai:dahl.mattias"Sakovich, Anna"https://www.zbmath.org/authors/?q=ai:sakovich.annaSummary: When working with asymptotically hyperbolic initial data sets for general relativity it is convenient to assume certain simplifying properties. We prove that the subset of initial data sets with such properties is dense in the set of physically reasonable asymptotically hyperbolic initial data sets. More specifically, we show that an asymptotically hyperbolic initial data set with nonnegative local energy density can be approximated by an initial data set with strictly positive local energy density and a simple structure at infinity, while changing the mass arbitrarily little. This is achieved by suitably modifying the argument used by \textit{M. Eichmair} et al. [J. Eur. Math. Soc. (JEMS) 18, No. 1, 83--121 (2016; Zbl 1341.53067)] in the asymptotically Euclidean case.Spin weighted wavelets on the sphere -- frameshttps://www.zbmath.org/1483.420242022-05-16T20:40:13.078697Z"Iglewska-Nowak, I."https://www.zbmath.org/authors/?q=ai:iglewska-nowak.ilonaSummary: A new construction of spin weighted wavelets on the sphere is presented in the paper. The wavelets are similar to those derived from approximate identities but the constraints of the definition are slightly weaker. They allow for quite a big freedom in wavelet construction so that even spin weighted wavelets with explicit representations exist. The price to be paid is that no direct reconstruction is given and the wavelet transform must be inverted with frame methods. The set of wavelet coefficients is a priori continuous but it is shown how it can be discretized so that no information about the analyzed signal get lost.Static Einstein-Maxwell space-time invariant by translationhttps://www.zbmath.org/1483.530382022-05-16T20:40:13.078697Z"Leandro, Benedito"https://www.zbmath.org/authors/?q=ai:leandro.benedito"de Melo, Ana Paula"https://www.zbmath.org/authors/?q=ai:de-melo.ana-paula"Menezes, Ilton"https://www.zbmath.org/authors/?q=ai:menezes.ilton"Pina, Romildo"https://www.zbmath.org/authors/?q=ai:pina.romildo-da-silva|pina.romildo-sSummary: In this paper we study the static Einstein-Maxwell space when it is conformal to an \(n\)-dimensional pseudo-Euclidean space, which is invariant under the action of an \((n-1)\)-dimensional translation group. We also provide a complete classification of such space.A note on the Gannon-Lee theoremhttps://www.zbmath.org/1483.530392022-05-16T20:40:13.078697Z"Schinnerl, Benedict"https://www.zbmath.org/authors/?q=ai:schinnerl.benedict"Steinbauer, Roland"https://www.zbmath.org/authors/?q=ai:steinbauer.rolandSummary: We prove a Gannon-Lee theorem for non-globally hyperbolic Lorentzian metrics of regularity \(C^1\), the most general regularity class currently available in the context of the classical singularity theorems. Along the way, we also prove that any maximizing causal curve in a \(C^1\)-spacetime is a geodesic and hence of \(C^2\)-regularity.Inevitability of the Poisson bracket structure of the relativistic constraintshttps://www.zbmath.org/1483.530412022-05-16T20:40:13.078697Z"Głowacki, Jan"https://www.zbmath.org/authors/?q=ai:glowacki.janSummary: The purpose of this paper is to shed some fresh light on the long-standing conceptual question of the \textit{origin} of the well-known Poisson bracket structure of the constraints that govern the canonical dynamics of generally relativistic field theories, i.e. geometrodynamics. This structure has long been known to be the same for a wide class of fields that inhabit the space-time, namely those with non-differential coupling to gravity. It has also been noticed that an identical bracket structure can be derived independently of any dynamical theory, by \textit{purely geometrical} considerations in Lorentzian geometry. Here we attempt to provide the missing link between the dynamics and geometry, which we understand to be the \textit{reason} for this structure to be of the specific kind. We achieve this by a careful analysis of the geometrodynamical approach, which allows us to \textit{derive} the structure in question and understand it as a \textit{consistency requirement} for any such theory. In order to stay close to the classical literature on the subject we stick to the metric formulation of general relativity, but the reasoning should carry over to any other formulation as long as the non-metricity tensor vanishes. The discussion section is devoted to derive some interesting consequences of the presented result in the context of reconstructing the Arnowitt-Deser-Misner (ADM) framework, thus providing a precise sense to the inevitability of the Einstein's theory under minimal assumptions.On center of mass and foliations by constant spacetime mean curvature surfaces for isolated systems in general relativityhttps://www.zbmath.org/1483.530862022-05-16T20:40:13.078697Z"Cederbaum, Carla"https://www.zbmath.org/authors/?q=ai:cederbaum.carla"Sakovich, Anna"https://www.zbmath.org/authors/?q=ai:sakovich.annaThe authors define a new total center of mass for an ``isolated system'': the ``Universe'' is a 4-dimensional Lorentzian manifold \((\mathfrak M^{1,3}, \mathfrak{g})\), endowed with an energy-momentum tensor field \(\mathfrak T\), with an ``initial data set'' given by a spacelike hypersuface \((M^3,g)\), with the second fundamental form \(K\), the scalar local energy density \(\mu\) and the (1-form) local momentum density \(J\). When this configuration is ``asymptotically Euclidean'' and with non-vanishing energy, it gives rise to a (unique) foliation by 2-spheres of constant spacetime mean curvature. This foliation is the main tool for constructing the total center of mass. It is shown that this center of mass behaves as a point particle in Special Relativity (i.e. it transforms equivariantly under the asymptotic Poincaré group of \({\mathfrak M^{1,3}}\)). In particular, it evolves in time under the Einstein evolution equations like a point particle in Special Relativity.
Reviewer: Gabriel Teodor Pripoae (Bucureşti)A note on the Sagnac effect in general relativity as a Finslerian effecthttps://www.zbmath.org/1483.530892022-05-16T20:40:13.078697Z"Caponio, Erasmo"https://www.zbmath.org/authors/?q=ai:caponio.erasmo"Masiello, Antonio"https://www.zbmath.org/authors/?q=ai:masiello.antonioSummary: The geometry of the Sagnac effect in a stationary region of a spacetime is reviewed with the aim of emphasizing the role of asymmetry of a Finsler metric defined on a spacelike hypersurface associated to a stationary splitting and related to future-pointing null geodesics of the spacetime. We show also that an analogous asymmetry comes into play in the Sagnac effect for timelike geodesics.Geometric flux formula for the gravitational Wilson loophttps://www.zbmath.org/1483.530912022-05-16T20:40:13.078697Z"Klitgaard, N."https://www.zbmath.org/authors/?q=ai:klitgaard.n"Loll, R."https://www.zbmath.org/authors/?q=ai:loll.renate"Reitz, M."https://www.zbmath.org/authors/?q=ai:reitz.m"Toriumi, R."https://www.zbmath.org/authors/?q=ai:toriumi.reikoThis paper is concerned with finding quantities, constructed out of gravitational holonomies of the Levi-Civita connection, that can be used to obtain information about the curvature of a given manifold. The authors motivate the search by possible applications in nonperturbative quantum gravity, e.g. in the causal dynamical triangulation approach. The main idea is to use Wilson loops as a basic tool and formulate a certain type of generalized Stokes theorem.
The authors first revisit holonomies for infinitesimal loops on Riemannian manifolds and discuss certain nonabelian version of the Stokes theorem for finite (contractible) loops which are boundaries of a given surface \(S\). Schematically, it can be written as
\[
P e^{-\oint_{\partial S}\Gamma}=\mathcal{P} e^{-\int_S \widetilde{R}},
\]
where \(P\) is the path-ordering and \(\mathcal{P}\) is a specific type of surface-ordering considered by the authors. Here, again schematically, \(\Gamma\) denotes the Levi-Civita connection with curvature \(R\), and \(\widetilde{R}\) is the curvature \(R\) parallely-transported to a chosen base point of the surface \(S\). The right hand side is therefore a highly nonlocal object that encodes information about the curvature. Furthermore, the non-uniqueness of the choice of a surface-ordering leads to problems with the interpretation of this quantity. It is therefore natural to ask for a similar relation between holonomies for finite loops and averaging curvature-like quantities, which is free of this issue even for the case with nonabelian holonomy group.
The authors show that there is a class of manifolds, possessing foliation by a family of totally geodesic surfaces, for which this problem can be solved. They study three and four dimensional manifolds with hypersurface-orthogonal Killing vector fields, whose presence is suficient for the existence of totally geodesic surfaces. The authors then find associated geometric fluxes and use them to prove (with the help of the classical Stokes theorem) that the quantity, defined in terms of the integral from the curvature-like quantity over the surface being the boundary of the given loop, is invariant under smooth deformations of this surface that leave the boundary untouched.
Reviewer: Arkadiusz Bochniak (Kraków)A method for estimating the statistical error of the solution in the inverse spectroscopy problemhttps://www.zbmath.org/1483.622062022-05-16T20:40:13.078697Z"Bannikova, Tat'yana Mikhaĭlovna"https://www.zbmath.org/authors/?q=ai:bannikova.tatyana-mikhailovna"Nemtsov, Viktor Mikhaĭloich"https://www.zbmath.org/authors/?q=ai:nemtsov.viktor-mikhailoich"Baranova, Natal'ya Anatol'evna"https://www.zbmath.org/authors/?q=ai:baranova.natalya-anatolevna"Konygin, Grigorĭ Nikolaevich"https://www.zbmath.org/authors/?q=ai:konygin.grigori-nikolaevich"Nemtsova, Ol'ga Mikhaĭlovna"https://www.zbmath.org/authors/?q=ai:nemtsova.olga-mikhailovnaSummary: A method for obtaining the interval of statistical error of the solution of the inverse spectroscopy problem, for the estimation of the statistical error of experimental data of which the normal distribution law can be applied, has been proposed. With the help of mathematical modeling of the statistical error of partial spectral components obtained from the numerically stable solution of the inverse problem, it has become possible to specify the error of the corresponding solution. The problem of getting the inverse solution error interval is actual because the existing methods of solution error evaluation are based on the analysis of smooth functional dependences under rigid restrictions on the region of acceptable solutions (compactness, monotonicity, etc.). Their use in computer processing of real experimental data is extremely difficult and therefore, as a rule, is not applied. Based on the extraction of partial spectral components and the estimation of their error, a method for obtaining an interval of statistical error for the solution of inverse spectroscopy problems has been proposed in this work. The necessity and importance of finding the solution error interval to provide reliable results is demonstrated using examples of processing Mössbauer spectra.Domain uncertainty quantification in computational electromagneticshttps://www.zbmath.org/1483.650102022-05-16T20:40:13.078697Z"Aylwin, Ruben"https://www.zbmath.org/authors/?q=ai:aylwin.ruben"Jerez-Hanckes, Carlos"https://www.zbmath.org/authors/?q=ai:jerez-hanckes.carlos"Schwab, Christoph"https://www.zbmath.org/authors/?q=ai:schwab.christoph"Zech, Jakob"https://www.zbmath.org/authors/?q=ai:zech.jakobContextuality, fine-tuning and teleological explanationhttps://www.zbmath.org/1483.810032022-05-16T20:40:13.078697Z"Adlam, Emily"https://www.zbmath.org/authors/?q=ai:adlam.emily-christineSummary: I assess various proposals for the source of the intuition that there is something problematic about contextuality, ultimately concluding that contextuality is best thought of in terms of fine-tuning. I then argue that as with other fine-tuning problems in quantum mechanics, this behaviour can be understood as a manifestation of teleological features of physics. Finally I discuss several formal mathematical frameworks that have been used to analyse contextuality and consider how their results should be interpreted by scientific realists. In the course of this discussion I obtain several new mathematical results -- I demonstrate that preparation contextuality is a form of fine-tuning, I show that measurement contextuality can be explained by appeal to a global constraint forbidding closed causal loops, and I demonstrate how negative probabilities can arise from a classical ontological model together with an epistemic restriction.Fundamental limit on angular measurements and rotations from quantum mechanics and general relativityhttps://www.zbmath.org/1483.810132022-05-16T20:40:13.078697Z"Calmet, Xavier"https://www.zbmath.org/authors/?q=ai:calmet.xavier"Hsu, Stephen D. H."https://www.zbmath.org/authors/?q=ai:hsu.stephen-d-hSummary: We show that the precision of an angular measurement or rotation (e.g., on the orientation of a qubit or spin state) is limited by fundamental constraints arising from quantum mechanics and general relativity (gravitational collapse). The limiting precision is \(r^{-1}\) in Planck units, where \(r\) is the physical extent of the (possibly macroscopic) device used to manipulate the spin state. This fundamental limitation means that spin states \(S_1\) and \(S_2\) cannot be experimentally distinguished from each other if they differ by a sufficiently small rotation. Experiments cannot exclude the possibility that the space of quantum state vectors (i.e., Hilbert space) is fundamentally discrete, rather than continuous. We discuss the implications for finitism: does physics require infinity or a continuum?The quantum Otto heat engine with a relativistically moving thermal bathhttps://www.zbmath.org/1483.810462022-05-16T20:40:13.078697Z"Papadatos, Nikolaos"https://www.zbmath.org/authors/?q=ai:papadatos.nikolaosSummary: We investigate the quantum thermodynamic cycle of a quantum heat engine carrying out an Otto thermodynamic cycle. We use the thermal properties of a moving heat bath with relativistic velocity with respect to the cold bath. As a working medium, we use a two-level system and a harmonic oscillator that interact with a hot and cold bath respectively. In the current work, the quantum heat engine is studied in the high and low temperatures regime. Using quantum thermodynamics and the theory of open quantum systems we obtain the total produced work, the efficiency and the efficiency at maximum power. The maximum efficiency of the Otto quantum heat engine depends only on the ratio of the minimum and maximum energy gaps. On the contrary, the efficiency at maximum power and the extracted work decreases with the velocity since the motion of the heat bath has an energy cost for the quantum heat engine. Furthermore, the efficiency at maximum power depends on the nature of the working medium.Exciton stability and luminescence in InN/(In,Ga)N quantum dots under size and shell content effectshttps://www.zbmath.org/1483.810772022-05-16T20:40:13.078697Z"Benhaddou, Farid"https://www.zbmath.org/authors/?q=ai:benhaddou.farid"El Ghazi, Haddou"https://www.zbmath.org/authors/?q=ai:el-ghazi.haddou"Abboudi, Hassan"https://www.zbmath.org/authors/?q=ai:abboudi.hassan"Zorkani, Izeddine"https://www.zbmath.org/authors/?q=ai:zorkani.izeddine"Jorio, Anouar"https://www.zbmath.org/authors/?q=ai:jorio.anouarSummary: The electronic structure and associated excitonic properties of core/shell nanocrystals based on InN/(In,Ga)N quantum dots with InN-core and (In,Ga)N-shell are investigated numerically using perturbation theory. The shell In(Ga)N and ligand in this nanocrystal strengthen confinement, passivate the structure, and improve the InN optical characteristics. Such confinement is modelled by a finite potential considering the effective mass and dielectric constant mismatches between the core and shell. The impacts of Indium-content and quantum dot size on charge carrier position, excitonic states, excitonic binding energy, exciton stability, effective band-gap, and fundamental excitonic transition are investigated. Our numerical results reveal that the quantum dots size and Indium-content can be used to tailor nanocrystals and their luminescence properties for eventual opto-electronic applications. It is found that the exciton is more stable at room temperature in nanostrucure with lower Indium-content and thin core.Existence of relativistic dynamics for two directly interacting Dirac particles in \(1+3\) dimensionshttps://www.zbmath.org/1483.810782022-05-16T20:40:13.078697Z"Lienert, Matthias"https://www.zbmath.org/authors/?q=ai:lienert.matthias"Nöth, Markus"https://www.zbmath.org/authors/?q=ai:noth.markusThe ladder operators on \(1+1\)-de Sitter spacehttps://www.zbmath.org/1483.810892022-05-16T20:40:13.078697Z"Rabeie, A."https://www.zbmath.org/authors/?q=ai:rabeie.a"Rezaei, S."https://www.zbmath.org/authors/?q=ai:rezaei.sadegh|rezaei.seyed-saeed-changi|rezaei.sara|rezaei.shahed|rezaei.shahram|rezaei.shadi|rezaei.shahrbanoo|rezaei.seyed-mehdi|rezaei.shayesteh|rezaei.saeidSummary: In this paper, we present the annihilation and creation operators for a moving scalar massive particle on \(1+1\)-de Sitter space. This presentation is based on coherent states method and Hall-Mitchell approach about annihilation operator for a system which its phase space is \(S_{\mathcal{C}}^n \). We show that these operators coincide with the Ladder operators for a quantum particle on circle which was presented by Kowalski-Rembielinski-Papaloucas (both cases have the same phase spaces).Spinorial Snyder and Yang models from superalgebras and noncommutative quantum superspaceshttps://www.zbmath.org/1483.810912022-05-16T20:40:13.078697Z"Lukierski, Jerzy"https://www.zbmath.org/authors/?q=ai:lukierski.jerzy"Woronowicz, Mariusz"https://www.zbmath.org/authors/?q=ai:woronowicz.mariuszSummary: The relativistic Lorentz-covariant quantum space-times obtained by Snyder can be described by the coset generators of (anti) de-Sitter algebras. Similarly, the Lorentz-covariant quantum phase spaces introduced by Yang, which contain additionally quantum curved fourmomenta and quantum-deformed relativistic Heisenberg algebra, can be defined by suitably chosen coset generators of conformal algebras. We extend such algebraic construction to the respective superalgebras, which provide quantum Lorentz-covariant superspaces (SUSY Snyder model) and indicate also how to obtain the quantum relativistic phase superspaces (SUSY Yang model). In last Section we recall briefly other ways of deriving quantum phase (super)spaces and we compare the spinorial Snyder type models defining bosonic or fermionic quantum-deformed spinors.A numbers-based approach to a free particle's proper spacetimehttps://www.zbmath.org/1483.810922022-05-16T20:40:13.078697Z"Ferber, R."https://www.zbmath.org/authors/?q=ai:ferber.reginaldSummary: This paper contains a proposal for a free, nonzero-rest-mass particle's proper spacetime, determined exclusively by the particle's rest mass \(m_0\) and numbers. The approach defines proper time as de Broglie time, which is isomorphic to a sequence of natural numbers \(1, 2, \ldots\) that count de Broglie time units \((h/c^2)(m_0^{-1}\) (see \textit{R. Ferber} in [Found. Phys. Lett. 9, No. 6, 575--586 (1996,; \url{doi:10.1007/BF02190032})]. The approach is based on defining the spatial coordinate as proper following the constructive definition of positive and negative integers as all possible differences of ordered pairs of natural numbers multiplied by the Compton unit \((h/c)(m_0^{-1})\). The spatial and temporal coordinates that form the particle's proper spacetime are constructed as Euclidean projections of the de Broglie time. The corresponding expression in the form of an energy-momentum relation reveals the existence, aside from the rest energy term \(m_0c^2\), of an additional energy term of the same order of magnitude, which is related to large intervals of the \(m_0\)-particle's proper space. The relation of the numbers-based approach to the foundations of the special theory of relativity and of quantum mechanics is discussed.The D-CTC condition is generically fulfilled in classical (Non-quantum) statistical systemshttps://www.zbmath.org/1483.810962022-05-16T20:40:13.078697Z"Tolksdorf, Jürgen"https://www.zbmath.org/authors/?q=ai:tolksdorf.jurgen"Verch, Rainer"https://www.zbmath.org/authors/?q=ai:verch.rainerSummary: The D-CTC condition, introduced by David Deutsch as a condition to be fulfilled by analogues for processes of quantum systems in the presence of closed timelike curves, is investigated for classical statistical (non-quantum) bi-partite systems. It is shown that the D-CTC condition can generically be fulfilled in classical statistical systems, under very general, model-independent conditions. The central property used is the convexity and completeness of the state space that allows it to generalize Deutsch's original proof for q-bit systems to more general classes of statistically described systems. The results demonstrate that the D-CTC condition, or the conditions under which it can be fulfilled, is not characteristic of, or dependent on, the quantum nature of a bi-partite system.Correlation functions of \(\mathrm{U}(N)\)-tensor models and their Schwinger-Dyson equationshttps://www.zbmath.org/1483.810972022-05-16T20:40:13.078697Z"Pascalie, Romain"https://www.zbmath.org/authors/?q=ai:pascalie.romain"Pérez-Sánchez, Carlos I."https://www.zbmath.org/authors/?q=ai:perez-sanchez.carlos-ignacio"Wulkenhaar, Raimar"https://www.zbmath.org/authors/?q=ai:wulkenhaar.raimarSummary: We analyze the correlation functions of \(\mathrm{U}(N)\)-tensor models (or complex tensor models) and use the Ward-Takahashi identity in order to derive the full tower of exact, analytic Schwinger-Dyson equations. We write them explicitly for ranks \(D=3\) and \(D=4\). Throughout, we follow a non-perturbative approach. We propose the extension of this program to the Gurău-Witten model, a holographic tensor model based on the Sachdev-Ye-Kitaev model (SYK model).Erratum to: ``Reducible gauge symmetry versus unfree gauge symmetry in Hamiltonian formalism''https://www.zbmath.org/1483.810992022-05-16T20:40:13.078697Z"Abakumova, V. A."https://www.zbmath.org/authors/?q=ai:abakumova.v-a"Karataeva, I. Yu."https://www.zbmath.org/authors/?q=ai:karataeva.i-yu"Lyakhovich, S. L."https://www.zbmath.org/authors/?q=ai:lyakhovich.simon-lCorrects six formulas in the authors' paper [ibid. 973, Article ID 115577, 30 p. (2021; Zbl 1480.81088)].D-brane description from nontrivial M2-braneshttps://www.zbmath.org/1483.811182022-05-16T20:40:13.078697Z"Garcia del Moral, M. P."https://www.zbmath.org/authors/?q=ai:garcia-del-moral.maria-pilar"Las Heras, C."https://www.zbmath.org/authors/?q=ai:las-heras.cSummary: We obtain the bosonic D-brane description of toroidally compactified non-trivial M2-branes with the unique property of having a purely discrete supersymmetric regularized spectrum with finite multiplicity. As a byproduct, we generalize the previous Hamiltonian formulation to describe a M2-brane on a completely general constant quantized background \(C_3\) denoted by us as CM2-brane. We show that under this condition, the theory is equivalent to a more restricted one, denoted as an M2-brane with \(C_\pm\) fluxes, which has been shown to have good quantum behavior. As a result, the spectral properties of both sectors must be the same. We then obtain its bosonic D-brane description and discover new symmetries. We find that it contains a new symplectic gauge field in addition to the expected U(1) Dirac-Born-Infeld gauge symmetry and a nontrivial \(U(1)\) associated with the presence of 2-form fluxes. Its bundle description takes on a new structure in the form of a twisted torus bundle. By turning off some of the fields, the D-brane description of other toroidally nontrivial M2-brane sectors can be obtained from this one. The possibility of reinterpreting these sectors in terms of Dp-brane bound states is discussed. These D-brane descriptions constitute String theory sectors with a quantum consistent uplift to M-theory.Type IIB superstring vertex operator from the -8 picturehttps://www.zbmath.org/1483.811202022-05-16T20:40:13.078697Z"Martins, Lucas N. S."https://www.zbmath.org/authors/?q=ai:martins.lucas-n-sSummary: A new procedure was recently proposed for constructing massless Type IIB vertex operators in the pure spinor formalism. Instead of expressing these closed string vertex operators as left-right products of open string vertex operators, they were instead constructed from the complex N=2 d=10 superfield whose lowest real and imaginary components are the dilaton and Ramond-Ramond axion. These Type IIB vertex operators take a simple form in the -8 picture and are related to the usual vertex operators in the zero picture by acting with picture-raising operators. In this paper, we compute explicitly this picture-raising procedure and confirm this proposal in a flat background. Work is in progress on confirming this proposal in an \(AdS_5 \times S^5\) background.Finite-\(N\) corrections to the superconformal index of toric quiver gauge theorieshttps://www.zbmath.org/1483.811232022-05-16T20:40:13.078697Z"Arai, Reona"https://www.zbmath.org/authors/?q=ai:arai.reona"Fujiwara, Shota"https://www.zbmath.org/authors/?q=ai:fujiwara.shota"Imamura, Yosuke"https://www.zbmath.org/authors/?q=ai:imamura.yosuke"Mori, Tatsuya"https://www.zbmath.org/authors/?q=ai:mori.tatsuyaSummary: The superconformal index of quiver gauge theories realized on D3-branes in toric Calabi-Yau cones is investigated. We use the AdS/CFT correspondence and study D3-branes wrapped on supersymmetric cycles. We focus on brane configurations in which a single D3-brane is wrapped on a cycle, and we do not take account of branes with multiple wrapping. We propose a formula that gives finite-\(N\) corrections to the index caused by such brane configurations. We compare the predictions of the formula for several examples with the results on the gauge theory side obtained by using localization for small sizes of gauge groups, and confirm that the formula correctly reproduces the finite-\(N\) corrections up to the expected order.Holographic chaos, pole-skipping, and regularityhttps://www.zbmath.org/1483.811242022-05-16T20:40:13.078697Z"Natsuume, Makoto"https://www.zbmath.org/authors/?q=ai:natsuume.makoto"Okamura, Takashi"https://www.zbmath.org/authors/?q=ai:okamura.takashiSummary: We investigate the ``pole-skipping'' phenomenon in holographic chaos. According to pole-skipping, the energy-density Green's function is not unique at a special point in the complex momentum plane. This arises because the bulk field equation has two regular near-horizon solutions at the special point. We study the regularity of the two solutions more carefully using curvature invariants. In the upper-half \(\omega\)-plane, one solution, which is normally interpreted as the outgoing mode, is in general singular at the future horizon and produces a curvature singularity. However, at the special point, both solutions are indeed regular. Moreover, the incoming mode cannot be uniquely defined at the special point due to these solutions.Quantisation of Lorentz invariant scalar field theory in non-commutative space-time and its consequencehttps://www.zbmath.org/1483.811312022-05-16T20:40:13.078697Z"Harikumar, E."https://www.zbmath.org/authors/?q=ai:harikumar.e"Rajagopal, Vishnu"https://www.zbmath.org/authors/?q=ai:rajagopal.vishnuSummary: Quantisation of Lorentz invariant scalar field theory in Doplicher-Fredenhagen-Roberts (DFR) space-time, a Lorentz invariant, non-commutative space-time is studied. We use an approach to quantisation that is based on the equations of motion alone and derive the equal time commutation relation between Doplicher-Fredenhagen-Roberts-Amorim (DFRA) scalar field and its conjugate, which has non-commutative dependent modifications, but the corresponding creation and annihilation operators obey usual algebra.
We show that imposing the condition that the commutation relation between the field and its conjugate is same as that in the commutative space-time leads to a deformation of the algebra of quantised oscillators. Both these deformed commutation relations derived are valid to all orders in the non-commutative parameter. By analysing the first non-vanishing terms which are \(\theta^3\) order, we show that the deformed commutation relations scale as \(1/\lambda^4\), where \(\lambda\) is the length scale set by the non-commutativity of the space-time. We also derive the conserved currents for DFRA scalar field. Further, we analyse the effects of non-commutativity on Unruh effect by analysing a detector coupled to the DFRA scalar field, showing that the Unruh temperature is not modified but the thermal radiation seen by the accelerated observer gets correction due to the non-commutativity of space-time.Physics of the inverted harmonic oscillator: From the lowest Landau level to event horizonshttps://www.zbmath.org/1483.811392022-05-16T20:40:13.078697Z"Subramanyan, Varsha"https://www.zbmath.org/authors/?q=ai:subramanyan.varsha"Hegde, Suraj S."https://www.zbmath.org/authors/?q=ai:hegde.suraj-s"Vishveshwara, Smitha"https://www.zbmath.org/authors/?q=ai:vishveshwara.smitha"Bradlyn, Barry"https://www.zbmath.org/authors/?q=ai:bradlyn.barrySummary: In this work, we present the inverted harmonic oscillator (IHO) Hamiltonian as a paradigm to understand the quantum mechanics of scattering and time-decay in a diverse set of physical systems. As one of the generators of area preserving transformations, the IHO Hamiltonian can be studied as a dilatation generator, squeeze generator, a Lorentz boost generator, or a scattering potential. In establishing these different forms, we demonstrate the physics of the IHO that underlies phenomena as disparate as the Hawking-Unruh effect and scattering in the lowest Landau level (LLL) in quantum Hall systems. We derive the emergence of the IHO Hamiltonian in the LLL in a gauge invariant way and show its exact parallels with the Rindler Hamiltonian that describes quantum mechanics near event horizons. This approach of studying distinct physical systems with symmetries described by isomorphic Lie algebras through the emergent IHO Hamiltonian enables us to reinterpret geometric response in the lowest Landau level in terms of relativistic effects such as Wigner rotation. Further, the analytic scattering matrix of the IHO points to the existence of quasinormal modes (QNMs) in the spectrum, which have quantized time-decay rates. We present a way to access these QNMs through wave packet scattering, thus proposing a novel effect in quantum Hall point contact geometries that parallels those found in black holes.Electroweak phase transition in a complex singlet extension of the standard model with degenerate scalarshttps://www.zbmath.org/1483.811562022-05-16T20:40:13.078697Z"Cho, Gi-Chol"https://www.zbmath.org/authors/?q=ai:cho.gi-chol"Idegawa, Chikako"https://www.zbmath.org/authors/?q=ai:idegawa.chikako"Senaha, Eibun"https://www.zbmath.org/authors/?q=ai:senaha.eibunSummary: We study the feasibility of strong first-order electroweak phase transition (EWPT) in a degenerate-scalar scenario of a complex singlet extension of the Standard Model, in which a mass of an additional scalar is nearly degenerate with that of the Higgs boson, 125 GeV. This scenario is known to provide an exquisite solution for circumventing constraints from dark matter direct detection experiments due to cancellations between two scattering amplitudes mediated by two scalars. In the analysis of EWPT, we employ two gauge-invariant calculation schemes on the scalar potential and two familiar resummation methods in evaluating one-loop (gauge dependent) effective potential. We point out that one of the conditions for the strong first-order EWPT is incompatible with the known suppression mechanism of a dark matter cross-section scattering off the nucleons. Nevertheless, we find that strong first-order EWPT is still possible in the degenerate-scalar scenario by dodging dark matter constraints differently.Monopole hierarchy in transitions out of a Dirac spin liquidhttps://www.zbmath.org/1483.811642022-05-16T20:40:13.078697Z"Dupuis, Éric"https://www.zbmath.org/authors/?q=ai:dupuis.eric"Witczak-Krempa, William"https://www.zbmath.org/authors/?q=ai:witczak-krempa.williamSummary: Quantum spin liquids host novel emergent excitations, such as monopoles of an emergent gauge field. Here, we study the hierarchy of monopole operators that emerges at quantum critical points (QCPs) between a two-dimensional Dirac spin liquid and various ordered phases. This is described by a confinement transition of quantum electrodynamics in two spatial dimensions (QED\(_3\) Gross-Neveu theories) Focusing on a spin ordering transition, we get the scaling dimension of monopoles at leading order in a large-\(N\) expansion, where \(2 N\) is the number of Dirac fermions, as a function of the monopole's total magnetic spin. Monopoles with a maximal spin have the smallest scaling dimension while monopoles with a vanishing magnetic spin have the largest one, the same as in pure QED\(_3\). The organization of monopoles in multiplets of the QCP's symmetry group SU\((2)\times\)SU(N) is shown for general N.Extending light-front holographic QCD using the 't Hooft equationhttps://www.zbmath.org/1483.811752022-05-16T20:40:13.078697Z"Ahmady, Mohammad"https://www.zbmath.org/authors/?q=ai:ahmady.mohammad-r"Dahiya, Harleen"https://www.zbmath.org/authors/?q=ai:dahiya.harleen"Kaur, Satvir"https://www.zbmath.org/authors/?q=ai:kaur.satvir"Mondal, Chandan"https://www.zbmath.org/authors/?q=ai:mondal.chandan-kumar.1"Sandapen, Ruben"https://www.zbmath.org/authors/?q=ai:sandapen.ruben"Sharma, Neetika"https://www.zbmath.org/authors/?q=ai:sharma.neetikaSummary: We show the 't Hooft Equation and the light-front holographic Schrödinger Equation are complementary to each other in governing the transverse and longitudinal dynamics of colour confinement in quark-antiquark mesons. Together, they predict remarkably well the light, heavy-light and heavy-heavy meson spectroscopic data. The universal emerging hadronic scale of light-front holography, \(\kappa \approx 0.5\) GeV, controls the transverse dynamics of confinement in all these mesons. In heavy-heavy mesons, it also coincides numerically with the 't Hooft coupling which governs longitudinal confinement, thus reflecting the restoration of manifest 3-dimensional rotational symmetry.On the horizon entropy of a causal sethttps://www.zbmath.org/1483.830012022-05-16T20:40:13.078697Z"Machet, Ludovico"https://www.zbmath.org/authors/?q=ai:machet.ludovico"Wang, Jinzhao"https://www.zbmath.org/authors/?q=ai:wang.jinzhaoThe authors develop a relatively recent notion of a ``horizon molecule'', which is due to\textit{C. Barton}et al. [Phys. Rev. 100, No. 12, Article ID 126008, 17 p. (2019; \url{doi:10.1103/PhysRevD.100.126008})], which is defined on a causal set, to a setting with a null hypersurface crossing the horizon, which was discussed earlier by \textit{R. D. Sorkin} and \textit{Y. K. Yazdi} [Classical Quantum Gravity 35, No. 7, Article ID 074004, 17 p. (2018; Zbl 1390.83072)]. They argue that this notion fails to yield an entropy local to the hypersurface- horizon intersection in the continuum limit when the causal set approximates the curved spacetime. Subsequently the authors investigate the entopy defined via the spacetime mutual information between two regions of a ``causal diamond'' truncated by a causal horizon, and find, that it does limit to the area of the intersection.
Reviewer: Alex B. Gaina (Chişinău)Revisiting the evolving Lorentzian wormhole: a general perspectivehttps://www.zbmath.org/1483.830022022-05-16T20:40:13.078697Z"Bhattacharya, Subhra"https://www.zbmath.org/authors/?q=ai:bhattacharya.subhra"Bandyopadhyay, Tanwi"https://www.zbmath.org/authors/?q=ai:bandyopadhyay.tanwiSummary: Wormholes can be described as geometrical structures in space and time that can serve as connection between distant regions of the universe. Mathematically, general wormholes can be defined both on stationary as well as on dynamic line elements. However, general relativistic and evolving Lorentzian wormholes are less studied than their static wormhole counterpart. Accordingly, in this work we shall focus on some evolving wormhole geometries. Starting from a general class of spherically symmetric line element supporting wormhole geometries, we shall use the Einstein's field equations to develop viable astatic wormhole solutions. We will also discuss various evolving wormhole solutions together with their physical significance, properties and throat energy conditions. We claim that the method discussed in this work shall be applicable for developing wormhole solutions corresponding to any general Lorentzian wormhole metric.Anti-gravity à la Carlotto-Schoen [after Carlotto and Schoen]https://www.zbmath.org/1483.830032022-05-16T20:40:13.078697Z"Chruściel, Piotr T."https://www.zbmath.org/authors/?q=ai:chrusciel.piotr-tadeuszSummary: The Einstein equations have, essentially, a hyperbolic nature. Their solutions can therefore be obtained by evolving initial data in time. One of the difficulties of the theory is that the initial data are not arbitrary, but subject to constraint equations. In the case where the velocity-part of the initial data vanishes, the equations reduce to the prescribed-scalar-curvature equation, which is of geometric interest of its own.
One of the methods for the construction of initial data is the ``gluing method'', introduced by Corvino and Schoen. In my talk I will describe the method and review its applications. In particular I will describe a recent construction of Carlotto and Schoen which shows that
you can ``screen gravitational fields with gravitational fields'' by producing, for example, initial data which are exactly Minkowskian in one half-space and non-trivial in the other.
For the entire collection see [Zbl 1416.00029].Modeling of compact stars: an anisotropic approachhttps://www.zbmath.org/1483.830042022-05-16T20:40:13.078697Z"Das, Shyam"https://www.zbmath.org/authors/?q=ai:das.shyam"Singh, Ksh. Newton"https://www.zbmath.org/authors/?q=ai:singh.ksh-newton"Baskey, Lipi"https://www.zbmath.org/authors/?q=ai:baskey.lipi"Rahaman, Farook"https://www.zbmath.org/authors/?q=ai:rahaman.farook"Aria, Anil K."https://www.zbmath.org/authors/?q=ai:aria.anil-kSummary: We present here a new class of singularity free interior solutions relevant for the description of realistic anisotropic compact stellar objects with spherically symmetric matter distribution. In this geometric approach, specific choices of one of the metric functions and a selective anisotropic profile allow us to develop a stellar model by solving Einstein Field equations. The interior solutions thus obtained are matched with the Schwarzschild exterior metric over the bounding surface of a compact star. These matching conditions together with the condition that the radial pressure vanishes at the boundary are used to fix the model parameters. The different physical features for the developed model explicitly studied from the aspect of the pulsar 4U \(1820-30\) with its current estimated data (mass \(=1.46\pm 0.21~M\odot\) and radius \(=11.1\pm 1.8\) km [\textit{F. Özel} et al., ``The dense matter equation of state from neutron star radius and mass measurements'', Astrophys. J. 820, No. 1, Paper No. 28, 25 p. (2016)]. Analysis has shown that all the physical aspects are acceptable demanded for a physically admissible star and satisfy all the required physical conditions. The stability of the model is also explored in the context of causality conditions, adiabatic index, generalized Tolman-Oppenheimer-Volkov (TOV) equation, Buchdahl Condition and Herrera Cracking Method. To show that the developed model is compatible with a wide range of recently observed pulsars, various relevant physical variables are also highlighted in tabular form. The data studied here are in agreement with the observation of gravitational waves from the first binary merger event. Assuming a particular surface density \((7.5\times 10^{14}\text{ gm cm}^{-3})\), the mass-radius \((M-b)\) relationship and the radius-central density relationship \((b-\rho(0))\) of the compact stellar object are analyzed for this model. Additionally, comparing the results with a slow rotating configuration, we have also discussed moment of inertia and the time period using Bejger-Haensel idea.Particle motion in a space-time of a 3D Einstein gravity with torsionhttps://www.zbmath.org/1483.830052022-05-16T20:40:13.078697Z"Kaya, R."https://www.zbmath.org/authors/?q=ai:kaya.rustem"Özçelik, H. T."https://www.zbmath.org/authors/?q=ai:ozcelik.hasan-tuncaySummary: We analyze the motion of both massive and massless particles in a model with space-time of 3D Einstein gravity with torsion. We consider the spinor field and the massless scalar field as the source of torsion respectively. Following the Hamilton-Jacobi formalism, we investigate the effective potential of radial motion for test particles in a homogeneous and isotropic space-time with torsion. We show that there are no stable circular orbits for massive and massless particles in the Einstein gravity with torsion induced by the spinor field, in a space-time with two spatial and one time dimensions. In the case of massive particles, we show that stable orbits exist in 3D Einstein gravity with torsion induced by the scalar field.Spacetimes with continuous linear isotropies. I: Spatial rotationshttps://www.zbmath.org/1483.830062022-05-16T20:40:13.078697Z"MacCallum, M. A. H."https://www.zbmath.org/authors/?q=ai:maccallum.malcolm-a-hSummary: The weakest known criterion for local rotational symmetry (LRS) in spacetimes of Petrov type D is due to \textit{S. W. Goode} and \textit{J. Wainwright} [ibid. 18, 315--331 (1986; Zbl 0584.53029)]. Here it is shown, using methods related to the Cartan-Karlhede procedure, to be equivalent to local spatial rotation invariance of the Riemann tensor and its first derivatives. Conformally flat spacetimes are similarly studied and it is shown that for almost all cases the same criterion ensures LRS. Only for conformally flat accelerated perfect fluids are three curvature derivatives required to ensure LRS, showing that Ellis's original condition for that case is necessary as well as sufficient.Possible existence of a third fundamental long-range forcehttps://www.zbmath.org/1483.830072022-05-16T20:40:13.078697Z"Nakanishi, Noboru"https://www.zbmath.org/authors/?q=ai:nakanishi.noboru"Yoshida, Ritsu"https://www.zbmath.org/authors/?q=ai:yoshida.ritsuSummary: It is inferred that, in addition to the Coulomb and Newtonian forces, there should exist a third fundamental long-range force, which acts between intrinsic angular momenta. This inference is based on the quantum Einstein gravity, that is, the manifestly-covariant, BRS-invariant, canonically quantized theory of general relativity. The form of the potential of the third fundamental long-range force is determined by calculating the non-relativistic limit of the Bethe-Salpeter kernel in the lowest-order perturbation theory. The observability of this force is also discussed.Microscopic origin of Einstein's field equations and the \textit{raison d'être} for a positive cosmological constanthttps://www.zbmath.org/1483.830082022-05-16T20:40:13.078697Z"Padmanabhan, T."https://www.zbmath.org/authors/?q=ai:padmanabhan.thanu|padmanabhan.t-v"Chakraborty, Sumanta"https://www.zbmath.org/authors/?q=ai:chakraborty.sumantaSummary: In the paradigm of effective field theory, one hierarchically obtains the effective action \(\mathcal{A}_{\mathrm{eff}} [q, \cdots]\) for some low(er) energy degrees of freedom \(q\), by integrating out the high(er) energy degrees of freedom \(\xi\), in a path integral, based on an action \(\mathcal{A} [q, \xi, \cdots]\). We show how one can integrate out a vector field \(v^a\) in an action \(\mathcal{A} [\Gamma, v, \cdots]\) and obtain an effective action \(\mathcal{A}_{\mathrm{eff}}[\Gamma, \cdots]\) which, on variation with respect to the connection \(\Gamma\), leads to the Einstein's field equations and a metric compatible with the connection. The derivation \textit{predicts} a non-zero, positive, cosmological constant, which arises as an integration constant. The Euclidean action \(\mathcal{A} [\Gamma, v, \cdots]\), has an interpretation as the heat density of null surfaces, when translated into the Lorentzian spacetime. The vector field \(v^a\) can be interpreted as the Euclidean analogue of the microscopic degrees of freedom hosted by any null surface. Several implications of this approach are discussed.A wavefunction description for a localized quantum particle in curved spacetimeshttps://www.zbmath.org/1483.830092022-05-16T20:40:13.078697Z"Perche, T. Rick"https://www.zbmath.org/authors/?q=ai:perche.tales-rick"Neuser, Jonas"https://www.zbmath.org/authors/?q=ai:neuser.jonasQuasinormal resonances of rapidly-spinning Kerr black holes and the universal relaxation boundhttps://www.zbmath.org/1483.830102022-05-16T20:40:13.078697Z"Hod, Shahar"https://www.zbmath.org/authors/?q=ai:hod.shaharSummary: The universal relaxation bound suggests that the relaxation times of perturbed thermodynamical systems is bounded from below by the simple time-times-temperature (TTT) quantum relation \(\tau \times T \geq \frac{\hbar}{\pi}\). It is known that some perturbation modes of near-extremal Kerr black holes in the regime \(M T_{\mathrm{BH}}/\hbar \ll m^{-2}\) are characterized by normalized relaxation times \(\pi \tau \times T_{\mathrm{BH}}/\hbar\) which, in the approach to the limit \(M T_{\mathrm{BH}}/\hbar\to 0\), make infinitely many oscillations with a tiny constant amplitude around 1 and therefore cannot be used directly to verify the validity of the TTT bound in the entire parameter space of the black-hole spacetime (Here \(\{T_{\mathrm{BH}}, M\}\) are respectively the Bekenstein-Hawking temperature and the mass of the black hole, and \(m\) is the azimuthal harmonic index of the linearized perturbation mode). In the present compact paper we explicitly prove that all rapidly-spinning Kerr black holes respect the TTT relaxation bound. In particular, using analytical techniques, it is proved that all black-hole perturbation modes in the complementary regime \(m^{-1} \ll M T_{\mathrm{BH}}/\hbar\ll 1\) are characterized by relaxation times with the simple dimensionless property \(\pi \tau \times T_{\mathrm{BH}}/\hbar\geq 1\).Three-dimensional Maxwellian Carroll gravity theory and the cosmological constanthttps://www.zbmath.org/1483.830112022-05-16T20:40:13.078697Z"Concha, Patrick"https://www.zbmath.org/authors/?q=ai:concha.patrick"Peñafiel, Diego"https://www.zbmath.org/authors/?q=ai:penafiel.diego-m"Ravera, Lucrezia"https://www.zbmath.org/authors/?q=ai:ravera.lucrezia"Rodríguez, Evelyn"https://www.zbmath.org/authors/?q=ai:rodriguez.evelynSummary: In this work, we present the three-dimensional Maxwell Carroll gravity by considering the ultra-relativistic limit of the Maxwell Chern-Simons gravity theory defined in three spacetime dimensions. We show that an extension of the Maxwellian Carroll symmetry is necessary in order for the invariant tensor of the ultra-relativistic Maxwellian algebra to be non-degenerate. Consequently, we discuss the origin of the aforementioned algebra and theory as a flat limit. We show that the theoretical setup with cosmological constant yielding the extended Maxwellian Carroll Chern-Simons gravity in the vanishing cosmological constant limit is based on a new enlarged extended version of the Carroll symmetry. Indeed, the latter exhibits a non-degenerate invariant tensor allowing the proper construction of a Chern-Simons gravity theory which reproduces the extended Maxwellian Carroll gravity in the flat limit.Comment on: ``Do electromagnetic waves always propagate along null geodesics?''https://www.zbmath.org/1483.830122022-05-16T20:40:13.078697Z"Linnemann, Niels"https://www.zbmath.org/authors/?q=ai:linnemann.niels-s"Read, James"https://www.zbmath.org/authors/?q=ai:read.jamesErratum to: ``On the spectrum of primordial density fluctuations''https://www.zbmath.org/1483.830132022-05-16T20:40:13.078697Z"Pollock, M. D."https://www.zbmath.org/authors/?q=ai:pollock.martin-dCorrects seven typos in the author's paper [ibid. 15, No. 9, 1487--1499 (2006; Zbl 1120.83301)].Helicity and spin conservation in linearized gravityhttps://www.zbmath.org/1483.830142022-05-16T20:40:13.078697Z"Aghapour, Sajad"https://www.zbmath.org/authors/?q=ai:aghapour.sajad"Andersson, Lars"https://www.zbmath.org/authors/?q=ai:andersson.lars-erik|andersson.lars-ake|andersson.lars-l"Bhattacharyya, Reebhu"https://www.zbmath.org/authors/?q=ai:bhattacharyya.reebhuSummary: The duality-symmetric, Maxwell-like, formulation of linearized gravity introduced by \textit{S. M. Barnett} [New J. Phys. 16, No. 2, Article ID 023027, 23 p. (2014; Zbl 1451.83014)] is used to generalize the conservation laws for helicity, the spin part of angular momentum, and spin-flux, to the case of linearized gravity. These conservation laws have been shown to follow from the conservation property of the helicity array, an analog of Lipkin's zilch tensor. The analog of the helicity array for linearized gravity is constructed and is shown to be conserved.Propagation of gravitational waves in various cosmological backgroundshttps://www.zbmath.org/1483.830152022-05-16T20:40:13.078697Z"Mondal, Sushovan"https://www.zbmath.org/authors/?q=ai:mondal.sushovan"Ali, Saif"https://www.zbmath.org/authors/?q=ai:ali.saif"Shahul, Shanima"https://www.zbmath.org/authors/?q=ai:shahul.shanima"Banerjee, Narayan"https://www.zbmath.org/authors/?q=ai:banerjee.narayan"Hossain, Golam Mortuza"https://www.zbmath.org/authors/?q=ai:hossain.golam-mortuzaSummary: The present work investigates some exact solutions of the gravitational wave equation in some widely used cosmological spacetimes. The examples are taken from spatially flat and closed isotropic models as well as Kasner metric which is anisotropic. Various matter distributions are considered, from the standard dust or radiation distribution to exotic matters like that with an equation of state \(P=-\frac{1}{3}\rho\). In almost all cases the frequency and amplitude of the wave are found to be decaying with evolution, except for a closed radiation universe where there is a resurgence of the waveform, consistent with the recollapse of the universe into the big crunch singularity.Modifications to the signal from a gravitational wave event due to a surrounding shell of matterhttps://www.zbmath.org/1483.830162022-05-16T20:40:13.078697Z"Naidoo, Monos"https://www.zbmath.org/authors/?q=ai:naidoo.monos"Bishop, Nigel T."https://www.zbmath.org/authors/?q=ai:bishop.nigel-t"van der Walt, Petrus J."https://www.zbmath.org/authors/?q=ai:van-der-walt.petrus-jSummary: In previous work, we established theoretical results concerning the effect of matter shells surrounding a gravitational wave (GW) source, and we now apply these results to astrophysical scenarios. Firstly, it is shown that GW echoes that are claimed to be present in LIGO data of certain events, could not have been caused by a matter shell. However, it is also shown that there are scenarios in which matter shells could make modifications of order a few percent to a GW signal; these scenarios include binary black hole mergers, binary neutron star mergers, and core collapse supernovae.Quantum noise and vacuum fluctuations in balanced homodyne detections through ideal multi-mode detectorshttps://www.zbmath.org/1483.830172022-05-16T20:40:13.078697Z"Nakamura, Kouji"https://www.zbmath.org/authors/?q=ai:nakamura.koujiSummary: The balanced homodyne detection as a readout scheme of gravitational-wave detectors is carefully examined from the quantum field theoretical point of view. The readout scheme in gravitational-wave detectors specifies the directly measured quantum operator in the detection. This specification is necessary when we apply the recently developed quantum measurement theory to gravitational-wave detections. We examine the two models of measurement. One is the model in which the directly measured quantum operator at the photodetector is Glauber's photon number operator, and the other is the model in which the power operator of the optical field is directly measured. These two are regarded as ideal models of photodetectors. We first show these two models yield the same expectation value of the measurement. Since there is consensus in the gravitational-wave community that vacuum fluctuations contribute to the noises in the detectors, we also clarify the contributions of vacuum fluctuations to the quantum noise spectral density without using the two-photon formulation which is used in the gravitational-wave community. We found that the conventional noise spectral density in the two-photon formulation includes vacuum fluctuations from the main interferometer but does not include those from the local oscillator. Although the contribution of vacuum fluctuations from the local oscillator theoretically yields the difference between the above two models in the noise spectral densities, this difference is negligible in realistic situations.Baryon asymmetry from the generalized uncertainty principlehttps://www.zbmath.org/1483.830182022-05-16T20:40:13.078697Z"Das, Saurya"https://www.zbmath.org/authors/?q=ai:das.saurya"Fridman, Mitja"https://www.zbmath.org/authors/?q=ai:fridman.mitja"Lambiase, Gaetano"https://www.zbmath.org/authors/?q=ai:lambiase.gaetano"Vagenas, Elias C."https://www.zbmath.org/authors/?q=ai:vagenas.elias-cSummary: The unexplained observed baryon asymmetry in the Universe is a long-standing problem in physics, with no satisfactory resolution so far. To explain this asymmetry, three Sakharov conditions must be met. An interaction term which couples space-time and the baryon current is considered, which satisfies the first two Sakharov conditions. Furthermore, it is shown that the Generalized Uncertainty Principle (GUP) from quantum gravity induces corrections to the Friedmann equations in cosmology, via the holographic principle. GUP also induces variations of energy and pressure density in the radiation dominated era, which satisfies the third Sakharov condition. Therefore, this construction provides a viable explanation for the observed baryon asymmetry. This also fixes the GUP parameters to \(\alpha_0 \approx 10^4\) and \(\beta_0 \approx - 10^8\).Spacetimes with continuous linear isotropies. II: Boostshttps://www.zbmath.org/1483.830192022-05-16T20:40:13.078697Z"MacCallum, M. A. H."https://www.zbmath.org/authors/?q=ai:maccallum.malcolm-a-hSummary: Conditions are found which ensure that local boost invariance (LBI), invariance under a linear boost isotropy, implies local boost symmetry (LBS), i.e. the existence of a local group of motions such that for every point \(P\) in a neighbourhood there is a boost leaving \(P\) fixed. It is shown that for Petrov type D spacetimes this requires LBI of the Riemann tensor and its first derivative. That is also true for most conformally flat spacetimes, but those with Ricci tensors of Segre type [1(11,1)] may require LBI of the first three derivatives of curvature to ensure LBS.
For Parts I and III, see [the author, ibid. 53, No. 6, Paper No. 57, 21 p. (2021; Zbl 1483.83006); ibid. 53, No. 10, Paper No. 96, 22 p. (2021; Zbl 1483.83020)].Spacetimes with continuous linear isotropies. III: Null rotationshttps://www.zbmath.org/1483.830202022-05-16T20:40:13.078697Z"MacCallum, M. A. H."https://www.zbmath.org/authors/?q=ai:maccallum.malcolm-a-hSummary: It is shown that in many of the possible cases local null rotation invariance of the curvature and its first derivatives is sufficient to ensure that there is an isometry group \(G_r\) with \(r\ge 3\) acting on (a neighbourhood of) the spacetime and containing a null rotation isotropy. The exceptions where invariance of the second derivatives is additionally required to ensure this conclusion are Petrov type N Einstein spacetimes, spacetimes containing ``pure radiation'' (a Ricci tensor of Segre type [(11,2)]), and conformally flat spacetimes with a Ricci tensor of Segre type [1(11,1)] (a ``tachyon fluid'').
For Parts I and II, see [the author, ibid. 53, No. 6, Paper No. 57, 21 p. (2021; Zbl 1483.83006); ibid. 53, No. 6, Paper No. 61, 12 p. (2021; Zbl 1483.83019)].On the non-blow up of energy critical nonlinear massless scalar fields in `\(3+1\)' dimensional globally hyperbolic spacetimes: light cone estimateshttps://www.zbmath.org/1483.830212022-05-16T20:40:13.078697Z"Mondal, Puskar"https://www.zbmath.org/authors/?q=ai:mondal.puskarSummary: Here we prove a global existence theorem for the solutions of the semi-linear wave equation with critical non-linearity admitting a positive definite Hamiltonian. Formulating a parametrix for the wave equation in a globally hyperbolic curved spacetime, we derive an apriori pointwise bound for the solution of the nonlinear wave equation in terms of the initial energy, from which the global existence follows in a straightforward way. This is accomplished by two steps. First, based on Moncrief's light cone formulation we derive an expression for the scalar field in terms of integrals over the past light cone from an arbitrary spacetime point to an `initial', Cauchy hypersurface and additional integrals over the intersection of this cone with the initial hypersurface. Secondly, we obtain a priori estimates for the energy associated with three quasi-local approximate time-like conformal Killing and one approximate Killing vector fields. Utilizing these naturally defined energies associated with the physical stress-energy tensor together with the integral equation, we show that the spacetime \(L^\infty\) norm of the scalar field remains bounded in terms of the initial data and continues to be so as long as the spacetime remains singularity/Cauchy-horizon free.Mass and horizon Dirac observables in effective models of quantum black-to-white hole transitionhttps://www.zbmath.org/1483.830222022-05-16T20:40:13.078697Z"Bodendorfer, Norbert"https://www.zbmath.org/authors/?q=ai:bodendorfer.norbert"Mele, Fabio M."https://www.zbmath.org/authors/?q=ai:mele.fabio-m"Münch, Johannes"https://www.zbmath.org/authors/?q=ai:munch.johannesThere have been several recent studies of the black hole interior in loop quantum gravity, exploiting the isomorphism between the Schwarzschild interior and the Kantowski-Sachs spacetime. This allows the use of loop quantum cosmology techniques. The singularity that appears in the classical theory is resolved, replacing it with a black hole to white hole transition. Dirac observables have been identified associated with the mass of the black hole and the white hole and relations between them found. This paper further analyzes the issue of Dirac observables in these and other ``polymerized'' models.
Reviewer: Jorge Pullin (Baton Rouge)Dephasing and inhibition of spin interference from semi-classical self-gravitationhttps://www.zbmath.org/1483.830232022-05-16T20:40:13.078697Z"Großardt, André"https://www.zbmath.org/authors/?q=ai:grossardt.andreNon-local imprints of gravity on quantum theoryhttps://www.zbmath.org/1483.830242022-05-16T20:40:13.078697Z"Maziashvili, Michael"https://www.zbmath.org/authors/?q=ai:maziashvili.michael"Silagadze, Zurab K."https://www.zbmath.org/authors/?q=ai:silagadze.zurab-kSummary: During the last two decades or so much effort has been devoted to the discussion of quantum mechanics (QM) that in some way incorporates the notion of a minimum length. This upsurge of research has been prompted by the modified uncertainty relation brought about in the framework of string theory. In general, the implementation of minimum length in QM can be done either by modification of position and momentum operators or by restriction of their domains. In the former case we have the so called soccer-ball problem when the naive classical limit appears to be drastically different from the usual one. Starting with the latter possibility, an alternative approach was suggested in the form of a band-limited QM. However, applying momentum cutoff to the wave-function, one faces the problem of incompatibility with the Schrödinger equation. One can overcome this problem in a natural fashion by appropriately modifying Schrödinger equation. But incompatibility takes place for boundary conditions as well. Such wave-function cannot have any more a finite support in the coordinate space as it simply follows from the Paley-Wiener theorem. Treating, for instance, the simplest quantum-mechanical problem of a particle in an infinite potential well, one can no longer impose box boundary conditions. In such cases, further modification of the theory is in order. We propose a non-local modification of QM, which has close ties to the band-limited QM, but does not require a hard momentum cutoff. In the framework of this model, one can easily work out the corrections to various processes and discuss further the semi-classical limit of the theory.Loop quantum gravity and cosmological constanthttps://www.zbmath.org/1483.830252022-05-16T20:40:13.078697Z"Zhang, Xiangdong"https://www.zbmath.org/authors/?q=ai:zhang.xiangdong"Long, Gaoping"https://www.zbmath.org/authors/?q=ai:long.gaoping"Ma, Yongge"https://www.zbmath.org/authors/?q=ai:ma.yonggeSummary: A one-parameter regularization freedom of the Hamiltonian constraint for loop quantum gravity is analyzed. The corresponding spatially flat, homogenous and isotropic model includes the two well-known models of loop quantum cosmology as special cases. The quantum bounce nature is tenable in the generalized cases. For positive value of the regularization parameter, the effective Hamiltonian leads to an asymptotic de-Sitter branch of the Universe connecting to the standard Friedmann branch by the quantum bounce. Remarkably, by suitably choosing the value of the regularization parameter, the observational cosmological constant can emerge at large volume limit from the effect of quantum gravity, and the effective Newtonian constant satisfies the experimental restrictions in the meantime.5D \(\mathcal{N} = 1\) super QFT: symplectic quivershttps://www.zbmath.org/1483.830262022-05-16T20:40:13.078697Z"Saidi, E. H."https://www.zbmath.org/authors/?q=ai:saidi.el-hassan"Drissi, L. B."https://www.zbmath.org/authors/?q=ai:drissi.lalla-btissamSummary: We develop a method to build new 5D \(\mathcal{N} = 1\) gauge models based on Sasaki-Einstein manifolds \(Y^{p, q}\). These models extend the standard 5D ones having a unitary \(\mathrm{SU}(p)_q\) gauge symmetry based on \(Y^{p, q} \). Particular focus is put on the building of a gauge family with symplectic \(\mathrm{SP}(2r, \mathbb{R})\) symmetry. These super QFTs are embedded in M-theory compactified on folded toric Calabi-Yau threefolds \(\hat{X}(Y^{2r, 0})\) constructed from conical \(Y^{2r, 0}\). By using outer-automorphism symmetries of 5D \(\mathcal{N} = 1\) BPS quivers with unitary \(\mathrm{SU}(2r)\) gauge invariance, we also construct BPS quivers with symplectic \(\mathrm{SP}(2r, \mathbb{R})\) gauge symmetry. Other related aspects are discussed.Reply to comment on: ``Do electromagnetic waves always propagate along null geodesics?''https://www.zbmath.org/1483.830272022-05-16T20:40:13.078697Z"Asenjo, Felipe A."https://www.zbmath.org/authors/?q=ai:asenjo.felipe-a"Hojman, Sergio A."https://www.zbmath.org/authors/?q=ai:hojman.sergio-aExploration of a singular fluid spacetimehttps://www.zbmath.org/1483.830282022-05-16T20:40:13.078697Z"Remmen, Grant N."https://www.zbmath.org/authors/?q=ai:remmen.grant-nSummary: We investigate the properties of a special class of singular solutions for a self-gravitating perfect fluid in general relativity: the singular isothermal sphere. For arbitrary constant equation-of-state parameter \(w=p/\rho\), there exist static, spherically-symmetric solutions with density profile \(\propto 1/r^2\), with the constant of proportionality fixed to be a special function of \(w\). Like black holes, singular isothermal spheres possess a fixed mass-to-radius ratio independent of size, but no horizon cloaking the curvature singularity at \(r=0\). For \(w=1\), these solutions can be constructed from a homogeneous dilaton background, where the metric spontaneously breaks spatial homogeneity. We study the perturbative structure of these solutions, finding the radial modes and tidal Love numbers, and also find interesting properties in the geodesic structure of this geometry. Finally, connections are discussed between these geometries and dark matter profiles, the double copy, and holographic entropy, as well as how the swampland distance conjecture can obscure the naked singularity.Consistency between dynamical and thermodynamical stabilities for charged self-gravitating perfect fluidhttps://www.zbmath.org/1483.830292022-05-16T20:40:13.078697Z"Yang, Wei"https://www.zbmath.org/authors/?q=ai:yang.wei.4|yang.wei.2|yang.wei.3|yang.wei|yang.wei.1"Fang, Xiongjun"https://www.zbmath.org/authors/?q=ai:fang.xiongjun"Jing, Jiliang"https://www.zbmath.org/authors/?q=ai:jing.jiliangSummary: The entropy principle shows that, for self-gravitating perfect fluid, the Einstein field equations can be derived from the extrema of the total entropy, and the thermodynamical stability criterion are equivalent to the dynamical stability criterion. In this paper, we recast the dynamical criterion for the charged self-gravitating perfect fluid in Einstein-Maxwell theory, and further give the criterion of the star with barotropic condition. In order to obtain the thermodynamical stability criterion, first we get the general formula of the second variation of the total entropy for charged perfect fluid case, and then obtain the thermodynamical criterion for radial perturbation. We show that these two stability criterions are the same, which suggest that the inherent connection between gravity and thermodynamic even when the electric field is taken into account.Phase space analysis of Tsallis agegraphic dark energyhttps://www.zbmath.org/1483.830302022-05-16T20:40:13.078697Z"Huang, Hai"https://www.zbmath.org/authors/?q=ai:huang.hai"Huang, Qihong"https://www.zbmath.org/authors/?q=ai:huang.qihong"Zhang, Ruanjing"https://www.zbmath.org/authors/?q=ai:zhang.ruanjingSummary: Based on the generalized Tsallis entropy and holographic hypothesis, the Tsallis agegraphic dark energy (TADE) was proposed by introducing the timescale as infrared cutoff. In this paper, we analyze the evolution of the universe in the TADE model and the new Tsallis agegraphic dark energy (NTADE) model by considering an interaction between dark matter and dark energy as \(Q=H(\alpha\rho_m+\beta\rho_D)\). Through the phase space and stability analysis, we find an attractor which represents a late-time accelerated expansion phase can exist only in NTADE model. When \(0\leq\alpha<1\) and \(\beta=0\), this attractor becomes a dark energy dominated de Sitter solution and the universe can eventually evolve into an accelerated expansion era which is depicted by the \(\Lambda\) cold dark matter model. Thus, the expansion history of the universe can be depicted by the NTADE model.The new \((g -2)_\mu\) and right-handed sneutrino dark matterhttps://www.zbmath.org/1483.830312022-05-16T20:40:13.078697Z"Kim, Jong Soo"https://www.zbmath.org/authors/?q=ai:kim.jong-soo"López-Fogliani, Daniel E."https://www.zbmath.org/authors/?q=ai:lopez-fogliani.daniel-e"Perez, Andres D."https://www.zbmath.org/authors/?q=ai:perez.andres-d"de Austri, Roberto Ruiz"https://www.zbmath.org/authors/?q=ai:de-austri.roberto-ruizSummary: In this paper we investigate the \((g-2)_\mu\) discrepancy in the context of the R-parity conserving next-to-minimal supersymmetric Standard Model plus right-handed neutrinos superfields. The model has the ability to reproduce neutrino physics data and includes the interesting possibility to have the right-handed sneutrino as the lightest supersymmetric particle and a viable dark matter candidate. Since right-handed sneutrinos are singlets, no new contributions for \(\delta a_\mu\) with respect to the MSSM and NMSSM are present. However, the possibility to have the right-handed sneutrino as the lightest supersymmetric particle opens new ways to escape Large Hadron Collider and direct detection constraints. In particular, we find that dark matter masses within \(10 \lesssim m_{\widetilde{\nu}_R} \lesssim 600\) GeV are fully compatible with current experimental constraints. Remarkably, not only spectra with light sleptons are needed, but we obtain solutions with \(m_{\widetilde{\mu}} \gtrsim 600\) GeV in the entire dark matter mass range that could be probed by new \((g-2)_\mu\) data in the near future. In addition, dark matter direct detection experiments will be able to explore a sizable portion of the allowed parameter space with \(m_{\widetilde{\nu}_R} \lesssim 300\) GeV, while indirect detection experiments will be able to probe a much smaller fraction within \(200 \lesssim m_{\widetilde{\nu}_R} \lesssim 350\) GeV.Curvature perturbations and anomaly explain dark energyhttps://www.zbmath.org/1483.830322022-05-16T20:40:13.078697Z"Kitazawa, Yoshihisa"https://www.zbmath.org/authors/?q=ai:kitazawa.yoshihisaSummary: We investigate the history of dark energy to explain the present magnitude. We assume the dark energy is the residual cosmological constant. The most important channel in the reheating process is gluon pair production by the quantumchromodynamic trace anomaly. We argue that dark energy decays rapidly by gluon pair emissions during the reheating and after the big bang. The reheating temperature is determined by the decay width of dark energy, \(\Gamma\), and the Planck mass, \(M_{\mathrm{p}}\), as \(\sqrt{M_{\mathrm{P}}\Gamma} \sim 10^6 \, GeV\). This is a consequence of Friedmann's equation and the equilibrium condition \(\Gamma\sim H\). As the Universe cools below the hadronic scale, the dark energy density is almost frozen. Nevertheless, the dark energy further decreases by emitting two photons. We have estimated the current decay rate of dark energy from the quantum electrodynamic trace anomaly. The consistent solution of the Friedmann equation is in excellent agreement with the observations. The suppression factor of the dark energy scale is the product of the fine structure constant, \(\alpha\), and the curvature perturbation, \(P\): \(10^{-30}=(\alpha^2P/4\pi)^2\). We argue that the conformal symmetry breaking in both ultraviolet and infrared are necessary unless dark energy is subtracted. We also investigate leptogenesis by adding massive right-handed neutrinos: realistic leptogenesis takes place during the reheating process.Statistical approaches on the apparent horizon entropy and the generalized second law of thermodynamicshttps://www.zbmath.org/1483.830332022-05-16T20:40:13.078697Z"Abreu, Everton M. C."https://www.zbmath.org/authors/?q=ai:abreu.everton-m-c"Neto, Jorge Ananias"https://www.zbmath.org/authors/?q=ai:neto.jorge-ananiasSummary: In this work we have investigated the effects of three nongaussian entropies, namely, the modified Rényi entropy (MRE), the Sharma-Mittal entropy (SME) and the dual Kaniadakis entropy (DKE) in the investigation of the generalized second law (GSL) of thermodynamics violation. The GSL is an extension of the second law for black holes. Recently, it was concluded that a total entropy is the sum of the entropy enclosed by the apparent horizon plus the entropy of the horizon itself when the apparent horizon is described by the Barrow entropy. It was assumed that the universe is filled with matter and dark energy fluids. Here, the apparent horizon will be described by MRE, SME, and then by DKE proposals. Since GSL holds for usual entropy, but it is conditionally violated in the extended entropies, this implies that the parameter of these entropies should be constrained in small values in order to obey the GSL of thermodynamics. Hence, we have established conditions where the second law of thermodynamics can or cannot be obeyed considering these three statistical concepts just as it was made in Barrow's entropy. Considering the \(\Lambda CDM\) cosmology, we will notice that for MRE, SME and DKE, the GSL of thermodynamics is not obeyed for small redshift values.Scalar quasinormal modes for \(2+1\)-dimensional Coulomb-like AdS black holes from nonlinear electrodynamicshttps://www.zbmath.org/1483.830342022-05-16T20:40:13.078697Z"Aragón, Almendra"https://www.zbmath.org/authors/?q=ai:aragon.almendra"González, P. A."https://www.zbmath.org/authors/?q=ai:gonzalez.pablo-a-miranda"Saavedra, Joel"https://www.zbmath.org/authors/?q=ai:saavedra.joel"Vásquez, Yerko"https://www.zbmath.org/authors/?q=ai:vasquez.yerkoSummary: We study the propagation of scalar fields in the background of \(2+1\)-dimensional Coulomb-like AdS black holes, and we show that such propagation is stable under Dirichlet boundary conditions. Then, we solve the Klein-Gordon equation by using the pseudospectral Chebyshev method and the Horowitz-Hubeny method, and we find the quasinormal frequencies. Mainly, we find that the quasinormal frequencies are purely imaginary for a null angular number and they are complex and purely imaginary for a non-null value of the angular number, which depend on the black hole charge, angular number and overtone number. On the other hand, the effect of the inclusion of a Coulomb-like field from nonlinear electrodynamics to general relativity for a vanishing angular number is the emergence of two branches of quasinormal frequencies in contrast with the static BTZ black hole.QNMs of branes, BHs and fuzzballs from quantum SW geometrieshttps://www.zbmath.org/1483.830352022-05-16T20:40:13.078697Z"Bianchi, Massimo"https://www.zbmath.org/authors/?q=ai:bianchi.massimo"Consoli, Dario"https://www.zbmath.org/authors/?q=ai:consoli.dario"Grillo, Alfredo"https://www.zbmath.org/authors/?q=ai:grillo.alfredo"Morales, Francisco"https://www.zbmath.org/authors/?q=ai:morales.franciscoSummary: QNMs govern the linear response to perturbations of BHs, D-branes and fuzzballs and the gravitational wave signals in the ring-down phase of binary mergers. A remarkable connection between QNMs of neutral BHs in 4d and quantum SW geometries describing the dynamics of \(\mathcal{N} = 2\) SYM theories has been recently put forward. We extend the gauge/gravity dictionary to a large class of gravity backgrounds including charged and rotating BHs of Einstein-Maxwell theory in \(d = 4\), 5 dimensions, D3-branes, D1D5 `circular' fuzzballs and smooth horizonless geometries; all related to \(\mathcal{N} = 2\) SYM with a single \(SU(2)\) gauge group and fundamental matter. We find that photon-spheres, a common feature of all examples, are associated to degenerations of the classical elliptic SW geometry whereby a cycle pinches to zero size. Quantum effects resolve the singular geometry and lead to a spectrum of quantized energies, labelled by the overtone number \(n\). We compute the spectrum of QNMs using exact WKB quantization, geodetic motion and numerical simulations and show excellent agreement between the three methods. We explicitly illustrate our findings for the case D3-brane QNMs.Entropy of Reissner-Nordström-like black holeshttps://www.zbmath.org/1483.830362022-05-16T20:40:13.078697Z"Blagojević, M."https://www.zbmath.org/authors/?q=ai:blagojevic.milutin"Cvetković, B."https://www.zbmath.org/authors/?q=ai:cvetkovic.branislavSummary: In Poincaré gauge theory, black hole entropy is defined canonically by the variation of a boundary term \(\Gamma_H\), located at horizon. For a class of static and spherically symmetric black holes in vacuum, the explicit formula reads \(\delta \Gamma_H = T \delta S\), where \(T\) is black hole temperature and \(S\) entropy. Here, we analyze a new member of the same class, the Reissner-Nordström-like black hole with torsion [\textit{ J. A.R. Cembranos} and [\textit{J. G. Valcarcel}, ``New torsion black hole solutions in Poincaré gauge theory,'' J. Cosmol. Astropart. Phys., 01, Article 014 (2017; \url{doi:10.1088/1475-7516/2017/01/014})], where the electric charge of matter is replaced by a gravitational parameter, induced by the existence of torsion. This parameter affects \(\delta \Gamma_H\) in a way that ensures the validity of the first law.Generalized Dirac equation for a particle in a gravitational fieldhttps://www.zbmath.org/1483.830372022-05-16T20:40:13.078697Z"Chemisana, Daniel"https://www.zbmath.org/authors/?q=ai:chemisana.daniel"Giné, Jaume"https://www.zbmath.org/authors/?q=ai:gine.jaume"Madrid, Jaime"https://www.zbmath.org/authors/?q=ai:madrid.jaimeSummary: The existence of a minimal observable length modifies the Heisenberg's uncertainty principle at Plank scales and leads to some modifications of the Dirac equation. Here, we consider the generalized uncertainty principle (GUP) theory in order to deduce a generalized Dirac equation and solve its eigenvalue problem for a particle within a gravitational field created by a central mass. We use two different approximations to tackle the problem, based on the Schwarzschild and a modified Schwarzschild metrics.Numerical evolution of the interior geometry of charged black holeshttps://www.zbmath.org/1483.830382022-05-16T20:40:13.078697Z"Chesler, Paul M."https://www.zbmath.org/authors/?q=ai:chesler.paul-mSummary: Previously, we developed a late time approximation scheme to study the interior geometry of black holes. In the present paper we test this scheme with numerical relativity simulations. In particular, we present numerical relativity simulations of the interior geometry of charged spherically symmetric two-sided black holes with a spacelike singularity at \(r=0\). Our numerics are in excellent agreement with the late time approximatoin. We also demonstrate that the geometry near \(r=0\) is a scalarized Kasner geometry and compute the associated Kasner exponents.Geometry of Vaidya spacetimeshttps://www.zbmath.org/1483.830392022-05-16T20:40:13.078697Z"Coudray, Armand"https://www.zbmath.org/authors/?q=ai:coudray.armand"Nicolas, Jean-Philippe"https://www.zbmath.org/authors/?q=ai:nicolas.jean-philippeSummary: We investigate the geometrical structure of Vaidya's spacetime in the case of a white hole with decreasing mass, stabilising to a black hole in finite or infinite time or evaporating completely. Our approach relies on a detailed analysis of the ordinary differential equation describing the incoming principal null geodesics, among which are the generators of the past horizon. We devote special attention to the case of a complete evaporation in infinite time and establish the existence of an asymptotic light-like singularity of the conformal curvature, touching both the past space-like singularity and future time-like infinity. This singularity is present independently of the decay rate of the mass. We derive an explicit formula that relates directly the strength of this null singularity to the asymptotic behaviour of the mass function.On a conformal Schwarzschild-de Sitter spacetimehttps://www.zbmath.org/1483.830402022-05-16T20:40:13.078697Z"Culetu, Hristu"https://www.zbmath.org/authors/?q=ai:culetu.hristuSummary: On the basis of the C-metric, we investigate the conformal Schwarzschild - deSitter spacetime and compute the source stress tensor and study its properties, including the energy conditions. Then we analyze its extremal version \((b^2=27m^2\), where \(b\) is the deS radius and \(m\) is the source mass), when the metric is nonstatic. The weak-field
version is investigated in several frames, and the metric becomes flat with the special choice \(b=1/a\), \(a\) being the constant acceleration of the Schwarzschild-like mass or black hole. This form is Rindler's geometry in disguise and is also conformal to a de Sitter metric where the acceleration plays the role of the Hubble constant. In its time dependent version, one finds that the proper acceleration of a static observer is constant everywhere, in contrast with the standard Rindler case. The timelike geodesics along the z-direction are calculated and proves to be hyperbolae.Modeling the motion of a bright spot in jets from black holes M87* and SgrA*https://www.zbmath.org/1483.830412022-05-16T20:40:13.078697Z"Dokuchaev, Vyacheslav I."https://www.zbmath.org/authors/?q=ai:dokuchaev.vyacheslav-i"Nazarova, Natalia O."https://www.zbmath.org/authors/?q=ai:nazarova.natalia-oSummary: We study the general relativistic motion of a bright spot in a jet from an accreting black hole. The corresponding lensed images of the moving bright spot are calculated numerically in discrete time intervals along the bright spot trajectory in the Kerr space-time framework. As representative examples, we consider the cases of supermassive black holes SgrA* and M87*. Astrophysical observations of the moving bright spots in the jets from black holes provides the unique possibility for the verification of different gravitation theories in the strong field limit.Chiral and non-chiral spinning string dynamo instability from quantum torsion sourceshttps://www.zbmath.org/1483.830422022-05-16T20:40:13.078697Z"Garcia de Andrade, L. C."https://www.zbmath.org/authors/?q=ai:garcia-de-andrade.l-cSummary: In this paper dynamo instability is investigated by making use of a condensed matter screw dislocation model of spinning cosmic strings in the framework of teleparallel \(T_4\) spacetime, The magnetic field is encoded into the \(T_4\) metric tensor. By using quantum torsion from quantisation flux dependence on the spin angular momentum of strings, one is able to obtain dynamo instability where chiral currents grow exponentially as in Witten superconducting cosmic string. Our results are compared to [\textit{V. Galitsky} et al., Phys. Rev. Lett. 121, No. 17, Article ID 176603, 6 p. (2018; \url{doi:10.1103/PhysRevLett.121.176603})], who have investigated dynamo instability from Weyl semimetals, showing that chiral anomaly term reduces the Reynolds number for dynamo instability. String dynamos in the framework of Einstein-Cartan (EC) [the author, Cosmol. Astropart. Phys. 2014, No. 8, Paper No. 23, 9 p. (2014; \url{doi:10.1088/1475-7516/2014/08/023})], ER - [\textit{L. C. Garcia de Andrade}, Cosmic magnetism in modified theories of gravity. ChisinauÉditions universitaires europ'eennes (2017)] cosmology have been previously addressed. Moreover, it is shown that dynamo strings possess a monopole singularity at Big Bang. Topological defects dynamos, such as torsion spin-polarised fermions orthogonal to the wall [the author, Classical Quantum Gravity 38, No. 6, Article ID 065005, 9 p. (2021; Zbl 1479.83135)] have been obtained from torsional anomalies sources. Galitski et al. also discovered that chiral anomalies help dynamo effect in real magnetic fields. Non-chiral solutions where the current is along the string but the magnetic field is not, such as in pion string dynamo [\textit{R. Gwyn} et al., ``Magnetic fields from heterotic cosmic strings'', Phys. Rev. D (3) 79, No. 8, Article ID 083502, 13 p. (2009; \url{doi:10.1103/PhysRevD.79.083502})] are obtained from the Heaviside step function which tells us that the magnetic field grows, in the plane above \(z=0\) where the spinning string crosses the plane, and vanishes below the crossing plane.Black hole in Nielsen-Olesen vortexhttps://www.zbmath.org/1483.830432022-05-16T20:40:13.078697Z"Ghosh, Kumar J. B."https://www.zbmath.org/authors/?q=ai:ghosh.kumar-jang-bahadurSummary: In this article, we calculate the classical vortex solution of a spontaneously broken gauge theory interacting with gravity in (2+1)-dimension. We also calculate the conditions for the formation of a (2+1)-dimensional black hole due to magnetic vortex (a Nielsen-Olesen vortex). The semiclassical Hawking temperature for this black hole is calculated, where we see that the temperature of a BTZ black hole increases or decreases without changing the size of the horizon if we insert the magnetic vortex fields in the black hole. Finally, the first law of black hole thermodynamics is described for this particular solution, which shows that the additional work terms from the scalar and gauge fields compensate the change in the temperature relative to its usual value for the BTZ solution.Hawking radiation and particle dynamics in accelerating non-Kerr black holeshttps://www.zbmath.org/1483.830442022-05-16T20:40:13.078697Z"Gillani, Usman A."https://www.zbmath.org/authors/?q=ai:gillani.usman-a"Saifullah, Khalid"https://www.zbmath.org/authors/?q=ai:saifullah.khalidSummary: In this article we study Hawking radiation and particle dynamics for the recently discovered accelerating non-Kerr black holes. A critical analysis of incoming and outgoing, charged and uncharged scalar and Dirac particles, has been done. The Hawking temperature of massive and massless Dirac particles has been found in the background of accelerating non-Kerr black holes. The centre of mass energy of colliding particles has also been calculated and presented graphically. The classical expression of action for the massive and massless charged fermions is also worked out. We have compared our results with those that exist in the literature.Stability analysis of geodesics and quasinormal modes of a dual stringy black hole via Lyapunov exponentshttps://www.zbmath.org/1483.830452022-05-16T20:40:13.078697Z"Giri, Shobhit"https://www.zbmath.org/authors/?q=ai:giri.shobhit"Nandan, Hemwati"https://www.zbmath.org/authors/?q=ai:nandan.hemwatiSummary: We investigate the stability of both timelike as well as null circular geodesics in the vicinity of a dual (3+1) dimensional stringy black hole (BH) spacetime by using an excellent tool so-called Lyapunov exponent. The proper time \((\tau)\) Lyapunov exponent \((\lambda_p)\) and coordinate time \((t)\) Lyapunov exponent \((\lambda_c)\) are explicitly derived to analyze the stability of equatorial circular geodesics for the stringy BH spacetime with \textit{electric charge} parameter \((\alpha )\) and \textit{magnetic charge} parameter \((Q)\). By computing
these exponents for both the cases of BH spacetime, it is observed that the coordinate time Lyapunov exponent of magnetically charged stringy BH for both timelike and null geodesics are independent of magnetic charge parameter \((Q)\). The variation of the ratio of Lyapunov exponents with radius of timelike circular orbits \((r_0/M)\) for both the cases of stringy BH are presented. The behavior of instability exponent for null circular geodesics with respect to charge parameters \((\alpha\) and \(Q)\) are also observed for both the cases of BH. Further, by establishing a relation between quasinormal modes (QNMs) and parameters related to null circular geodesics (like angular frequency and Lyapunov exponent), we deduced the QNMs (or QNM frequencies) for a massless scalar field perturbation around \textit{both} the cases of stringy BH spacetime in the eikonal limit. The variation of scalar field potential with charge parameters and angular momentum of perturbation \((l)\) are visually presented and discussed accordingly.Schwarzschild-like black hole with a topological defect in bumblebee gravityhttps://www.zbmath.org/1483.830462022-05-16T20:40:13.078697Z"Güllü, İbrahim"https://www.zbmath.org/authors/?q=ai:gullu.ibrahim"Övgün, Ali"https://www.zbmath.org/authors/?q=ai:ovgun.aliSummary: In this paper, we derive an exact black hole spacetime metric in the Einstein-Hilbert-Bumblebee (EHB) gravity around global monopole field. We study the horizon, temperature, and the photon sphere of the black hole. Using the null geodesics equation, we obtain the shadow cast by the Schwarzschild-like black hole with a topological defect in Bumblebee gravity. Interestingly, the radius of shadow of the black hole increases with increase in the global monopole parameter. We also visualize the shadows and energy emission rates for different values of parameters. Moreover, using the Gauss-Bonnet theorem, we calculate the deflection angle in weak field limits and we discuss the possibility of testing the effect of global monopole field and bumblebee field, on a weak deflection angle. We find that the global monopole parameter and also Lorentz symmetry breaking parameter has an increasing effect on the deflection angle.An alternative to the Teukolsky equationhttps://www.zbmath.org/1483.830472022-05-16T20:40:13.078697Z"Hatsuda, Yasuyuki"https://www.zbmath.org/authors/?q=ai:hatsuda.yasuyukiSummary: We conjecture a new ordinary differential equation exactly isospectral to the radial component of the homogeneous Teukolsky equation. We find this novel relation by a hidden symmetry implied from a four-dimensional \(\mathcal{N}=2\) supersymmetric quantum chromodynamics. Our proposal is powerful both in analytical and in numerical studies. As an application, we derive high-order perturbative series of quasinormal mode frequencies in the slowly rotating limit. We also test our result numerically by comparing it with a known technique.Higher-dimensional non-extremal Reissner-Nordström black holes, scalar perturbation and superradiance: an analytical studyhttps://www.zbmath.org/1483.830482022-05-16T20:40:13.078697Z"Huang, Jia-Hui"https://www.zbmath.org/authors/?q=ai:huang.jiahui"Zhao, Run-Dong"https://www.zbmath.org/authors/?q=ai:zhao.rundong"Zou, Yi-Feng"https://www.zbmath.org/authors/?q=ai:zou.yi-fengSummary: The superradiant stability of asymptotically flat higher dimensional non-extremal Reissner-Nordstrom black holes under charged massive scalar perturbation is analytically studied. We extend an analytical method developed by one of the authors in the extremal Reissner-Nordstrom black hole cases to non-extremal cases. Using the new analytical method, we revisit four-dimensional Reissner-Nordstrom black hole case and obtain that four-dimensional Reissner-Nordstrom black hole is superradiantly stable, which is consistent with results in previous works. We then analytically prove that the five-dimensional Reissner-Nordstrom black holes are also superradiantly stable under charged massive scalar perturbation. Our result implies that all higher dimensional non-extremal Reissner-Nordstrom black holes may be superradiantly stable under charged massive scalar perturbation.Holographic complexity in charged accelerating black holeshttps://www.zbmath.org/1483.830492022-05-16T20:40:13.078697Z"Jiang, Shun"https://www.zbmath.org/authors/?q=ai:jiang.shun"Jiang, Jie"https://www.zbmath.org/authors/?q=ai:jiang.jie.2Summary: Using the ``complexity equals action'' (CA) conjecture, for an ordinary charged system, it has been shown that the late-time complexity growth rate is given by a difference between the value of \(\Phi_H Q + \Omega_H J\) on the inner and outer horizons. In this paper, we investigate the complexity of the boundary quantum system with conical deficits. From the perspective of holography, we consider charged accelerating black holes which contain conical deficits on the north and south poles in the bulk gravitational theory and evaluate the complexity growth rate using the CA conjecture. As a result, the late-time growth rate of complexity is different from the ordinary charged black holes. It implies that complexity can carry the information of conical deficits on the boundary quantum system.Correspondence between quasinormal modes and the shadow radius in a wormhole spacetimehttps://www.zbmath.org/1483.830502022-05-16T20:40:13.078697Z"Jusufi, Kimet"https://www.zbmath.org/authors/?q=ai:jusufi.kimetSummary: In this paper we study the correspondence between the real part of quasinormal modes and the shadow radius in a wormhole spacetime. Firstly we consider the above correspondence in a static and spherically symmetric wormhole spacetime and then explore this correspondence numerically by considering different wormhole models having specific redshift functions. To this end, we generalize this correspondence to the rotation wormhole spacetime and calculate the typical shadow radius of the rotating wormhole when viewed from the equatorial plane. We argue that due to the rotation and depending on the specific model, the typical shadow radius can increase or decrease and a reflecting point exists. Finally, we discuss whether a wormhole can mimic the black hole due to it's shadow. In the light of the EHT data, we find the upper and lower limits of the wormhole throat radius in the galactic center M87.Superradiance and stability of Kerr black hole enclosed by anisotropic fluid matterhttps://www.zbmath.org/1483.830512022-05-16T20:40:13.078697Z"Khodadi, Mohsen"https://www.zbmath.org/authors/?q=ai:khodadi.mohsen"Pourkhodabakhshi, Reza"https://www.zbmath.org/authors/?q=ai:pourkhodabakhshi.rezaSummary: Focusing on the rotating black hole (BH) surrounded by the anisotropic fluid matters; radiation, dust, and dark matter, we study the massive scalar superradiant scattering and the stability in the Kiselev spacetime. Superradiance behavior is dependent on the intensity parameter of the anisotropic matter \(K\) in the Kiselev spacetime. By adopting the manifest of low-frequency and low-mass for the scalar perturbation, we find \(K < 0\) enhances the superradiance scattering within the broader frequency range, compared to \(K = 0\) while \(K > 0\) suppresses within the narrower frequency range. As a result, the radiation and dark matter around the rotating BH act as amplifier and attenuator for the massive scalar superradiance, respectively. This is while the dust has a twofold role because of admitting both signs of \(K\). Through stability analysis in the light of the BH bomb mechanism, we show in the presence of dark matter, the instability regime of standard Kerr BH (\(K = 0\)) gets improved in favor of stabilization while the radiation and dust do not affect it. In other words, by taking the dark matter fluid around BH into account, we obtain a broader regime that allows the massive scalar field dynamic to enjoy superradiant stability.Configuration entropy and confinement-deconfinement transition in higher-dimensional hard wall modelhttps://www.zbmath.org/1483.830522022-05-16T20:40:13.078697Z"Lee, Chong Oh"https://www.zbmath.org/authors/?q=ai:lee.chong-ohSummary: We consider a higher-dimensional hard wall model with an infrared (IR) cut-off in asymptotically AdS space and investigate its thermodynamics via the holographic renormalization method. We find a relation between the confinement temperature and the IR cut-off for any dimension. It is also shown that the entropy of \(p\)-branes with the number of coincident branes (the number of the gauge group) \(N\) jumps from leading order in \(\mathcal{O}(N^0)\) at the confining low temperature phase to \(\mathcal{O}(N^{\frac{p + 1}{2}})\) at the deconfining high temperature phase like \(D3\)-branes (\(p = 3\)) case. On the other hand, we calculate the configuration entropy (CE) of various magnitudes of an inverse temperature at an given IR cut-off scale. It is shown that as the inverse temperature grows up, the CE above the critical temperature decreases and AdS black hole (BH) is stable while it below the critical temperature is constant and thermal AdS (ThAdS) is stable. In particular, we also find that the CE below the critical temperature becomes constant and its magnitude increases as a dimension of AdS space increases.Corrections to Hawking radiation and Bekenstein-Hawking entropy of novel four-dimensional black holes in Gauss-Bonnet gravityhttps://www.zbmath.org/1483.830532022-05-16T20:40:13.078697Z"Li, Gu-Qiang"https://www.zbmath.org/authors/?q=ai:li.guqiang"Mo, Jie-Xiong"https://www.zbmath.org/authors/?q=ai:mo.jie-xiong"Zhuang, Yi-Wen"https://www.zbmath.org/authors/?q=ai:zhuang.yi-wenSummary: We make use of the Hamilton-Jacobi and Parikh-Wilczek methods to investigate the Hawking radiation from the event horizon of a new charged anti-de Sitter black hole in four-dimensional Gauss-Bonnet gravity space-time. Both the tunneling rate of charged particles and the Bekenstein-Hawking entropy are evaluated. The emission spectrum is an impure thermal one and consistent with an underlying unitary theory. There is no difference between the emission rate of massive particle and that of massless one. The entropy is modified by a logarithmic term so that the area law of the black hole entropy is violated. It satisfies the first law of black hole thermodynamics and has the same expression as that calculated by Loop Quantum Gravity and String Theory. When the Gauss-Bonnet coupling coefficient is equal to zero, the logarithmic correction vanishes and the Bekenstein-Hawking relation in general relativity is recovered. So our results show the effects of the Gauss-Bonnet modified gravity on the Bekenstein-Hawking entropy and Hawking radiation.Thermodynamical critical properties of \(4D\) charged AdS massive black hole by thermo-shadow methodhttps://www.zbmath.org/1483.830542022-05-16T20:40:13.078697Z"Liu, Yun"https://www.zbmath.org/authors/?q=ai:liu.yun"Nie, Zhenxiong"https://www.zbmath.org/authors/?q=ai:nie.zhenxiong"Chen, Juhua"https://www.zbmath.org/authors/?q=ai:chen.juhua"Wang, Yongjiu"https://www.zbmath.org/authors/?q=ai:wang.yongjiuSummary: In this paper, we investigate the effect of the characteristic parameter \(m\) of the black hole solution in massive gravity on the thermodynamical critical properties of the black hole. We find that when the characteristic parameter \(m\) is less than the critical value \(m_c\), there is no the phase transition in the black hole system. On this basis, we use the black hole shadow radius to detect the phase transition of the \(4D\) charged AdS massive black hole in the extended phase space. The acquired result shows that the variation of thermodynamic quantities with shadow radius is very similar to that with event horizon radius. Using the shadow radius, we construct the black hole shadow thermal profile. By changing the temperature on the shadow contour, the Van der Waals-like phase transition can be clearly presented on the shadow contour.A note on size-momentum correspondence and chaoshttps://www.zbmath.org/1483.830552022-05-16T20:40:13.078697Z"Mahish, Sandip"https://www.zbmath.org/authors/?q=ai:mahish.sandip"Mohapatra, Shrohan"https://www.zbmath.org/authors/?q=ai:mohapatra.shrohan"Sil, Karunava"https://www.zbmath.org/authors/?q=ai:sil.karunava"Bhamidipati, Chandrasekhar"https://www.zbmath.org/authors/?q=ai:bhamidipati.chandrasekharSummary: The aim of this note is to explore \textit{L. Susskind}'s proposal [``Why do things fall?'', Preprint, \url{arXiv:1802.01198}] on the connection between operator size in chaotic theories and the bulk momentum of a particle falling into black holes (see also
[\textit{A. R. Brown} et al., ``Falling toward charged black holes'', Phys. Rev. D (3) 98, No. 12, Article ID 126016, 8 p. (2018, \url{doi:10.1103/PhysRevD.98.126016});
\textit{D. S. Ageev} and \textit{I. Ya. Aref'eva}, J. High Energy Phys. 2019, No. 1, Paper No. 100, 9 p. (2019; Zbl 1409.81101);
\textit{L. Susskind}, ``Complexity and Newton's laws'', Preprint, \url{arXiv:1904.12819};
\textit{J. L. F. Barbón} et al., J. High Energy Phys. 2020, No. 7, Paper No. 169, 23 p. (2020; Zbl 1451.83034);
\textit{L. Susskind} and \textit{Y. Zhao}, J. High Energy Phys. 2021, No. 3, Paper No. 239, 13 p. (2021; Zbl 1461.83021)]
for more recent generalizations), in a broad class of models involving Gauss-Bonnet(GB) and Lifshitz-Hyperscaling violating theories in AdS. For Gauss-Bonnet black holes, the operator size is seen to be suppressed as the coupling constant \(\lambda\) is increased. For the Lifshitz-hyperscaling violating theories characterised by the parameters \(z\) and \(\theta \), the operator size is higher as compared to case \(z = 1\), \(\theta = 0\) (Reissner-Nordstrom AdS black holes). In the case of operators with global charge corresponding to charged particles falling into black holes, suppression of chaos is seen in general theories of gravity, in conformity with the original proposal [Susskind, arXiv:1802.01198, loc. cit.] and earlier findings [Ageev and Aref'eva, loc. cit.].BMS Goldstone modes near the horizon of a Kerr black hole are thermalhttps://www.zbmath.org/1483.830562022-05-16T20:40:13.078697Z"Maitra, Mousumi"https://www.zbmath.org/authors/?q=ai:maitra.mousumi"Maity, Debaprasad"https://www.zbmath.org/authors/?q=ai:maity.debaprasad"Majhi, Bibhas Ranjan"https://www.zbmath.org/authors/?q=ai:majhi.bibhas-ranjanSummary: Near horizon Bondi-Metzner-Sachs (BMS) like symmetry is spontaneously broken by the black hole background itself and hence gives rise to Goldstone mode. The associated Goldstone mode for the near horizon BMS like symmetry of a Schwarzschild black hole was found to behave like inverted harmonic oscillators, which has been further shown to lead to thermodynamic temperature in the semi-classical regime. Here we investigate the generalization of this previous findings for the Kerr black hole. The analysis is being performed for two different situations. Firstly, we analyze Goldstone mode dynamics considering \textit{slowly rotating} Kerr. In other case the problem is solved in the frame of \textit{zero angular momentum observer} (ZAMO) with arbitrary value of rotation. In both analysis the effective semi-classical temperature of Goldstone modes turns out to be proportional to that of Hawking temperature. Due to such similarity and generality we feel that these Goldstone modes may play important role to understand the underlying microscopic description of horizon thermalization.Aliasing instabilities in the numerical evolution of the Einstein field equationshttps://www.zbmath.org/1483.830572022-05-16T20:40:13.078697Z"Meringolo, C."https://www.zbmath.org/authors/?q=ai:meringolo.c"Servidio, S."https://www.zbmath.org/authors/?q=ai:servidio.sergioSummary: The Einstein field equations of gravitation are characterized by cross-scale, high-order nonlinear terms, representing a challenge for numerical modeling. In an exact spectral decomposition, high-order nonlinearities correspond to a convolution that numerically might lead to aliasing instabilities. We present a study of this problem, in vacuum conditions, based on the \(3+1\) Baumgarte-Shibata-Shapiro-Nakamura (BSSN) formalism. We inspect the emergence of numerical artifacts, in a variety of conditions, by using the Spectral-FIltered Numerical Gravity codE (\texttt{SFINGE}) -- a pseudo-spectral algorithm, based on a classical (Cartesian) Fourier decomposition. By monitoring the highest \(k\)-modes of the dynamical
fields, we identify the culprits of the aliasing and propose procedures that cure such instabilities, based on the suppression of the aliased wavelengths. This simple algorithm, together with appropriate treatment of the boundary conditions, can be applied to a variety of gravitational problems, including those related to massive objects dynamics.Charged spherically symmetric Taub-NUT black hole solutions in \(f(R)\) gravityhttps://www.zbmath.org/1483.830582022-05-16T20:40:13.078697Z"Nashed, G. G. L."https://www.zbmath.org/authors/?q=ai:nashed.gamal-g-l"Bamba, Kazuharu"https://www.zbmath.org/authors/?q=ai:bamba.kazuharuSummary: \(f(R)\) theory is a modification of Einstein's general relativity which has provided many interesting results in cosmology and astrophysics. To derive a black hole solution in this theory is difficult due to the fact that it contains fourth-order differential equations. In this study, we use the first reliable deviation from general relativity which is given by the quadratic form of \(f(R)=R+\beta R^2\), where \(\beta\) is a dimensional parameter. We calculate the energy conditions of charged black holes and show that they are all satisfied for the Taub-NUT spacetime. Finally, we study some thermodynamic quantities such as entropy, temperature, specific heat, and Gibbs free energy. The calculations of heat capacity and free energy show that the charged Taub-NUT black hole has positive values, which means that it has thermal stability.Shadow and weak deflection angle of extended uncertainty principle black hole surrounded with dark matterhttps://www.zbmath.org/1483.830592022-05-16T20:40:13.078697Z"Pantig, Reggie C."https://www.zbmath.org/authors/?q=ai:pantig.reggie-c"Yu, Paul K."https://www.zbmath.org/authors/?q=ai:yu.paul-k-l"Rodulfo, Emmanuel T."https://www.zbmath.org/authors/?q=ai:rodulfo.emmanuel-t"Övgün, Ali"https://www.zbmath.org/authors/?q=ai:ovgun.aliSummary: In this paper, we discuss the possible effects of dark matter on a Schwarzschild black hole with the correction of extended uncertainty principle (EUP), such as the parameter \(\alpha\) and the large fundamental length scale \(L_\ast\). In particular, we surround the EUP black hole of mass \(m\) with a static spherical shell of dark matter described by the parameters mass \(M\), inner radius \(r_s\), and thickness \(\Delta r_s\). In this study, we find that there is no deviation in the event horizon, which readily implies that the black hole temperature due to the Hawking radiation is independent of any dark matter concentration. In addition, we show some effects of the EUP parameter on the innermost stable circular orbit (ISCO) radius of time-like particles, photon sphere, shadow radius, and weak deflection angle. It is found that time-like orbits are affected by deviation of low values of mass \(M\). A greater dark matter density is needed to have remarkable effects on the null orbits. Using the analytic expression for the shadow radius and the approximation \(\Delta r_s\gg r_s\), it is revealed that \(L_\ast\) should not be lower than \(2m\). To broaden the scope of this study, we also calculate the analytic expression for the weak deflection angle using the Ishihara et al. method [\textit{A. Ishihara} et al., ``Gravitational bending angle of light for finite distance and the Gauss-Bonnet theorem'', Phys. Rev. D 94, No. 8, Article ID 084015, 9 p. (2016; \url{doi:10.1103/PhysRevD.94.084015})]. As a result, we show that \(\Delta r_s\) is improved by a factor of \((1+4\alpha m^2/L_\ast^2)\) due to the EUP correction parameters. The calculated shadow radius and weak deflection angle are then compared using the estimated values of the galactic mass from Sgr A*, M87, and UGC 7232, as well as the mass of the supermassive black hole at their center.Energy formula for Newman-unti-tamburino class of black holeshttps://www.zbmath.org/1483.830602022-05-16T20:40:13.078697Z"Pradhan, Parthapratim"https://www.zbmath.org/authors/?q=ai:pradhan.parthapratimSummary: We compute the \textit{surface energy} \((\mathcal{E}_s^{\pm})\), \textit{the rotational energy} \((\mathcal{E}_r^\pm)\) \textit{and the electromagnetic energy} \((\mathcal{E}_{em}^\pm)\) for Newman-Unti-Tamburino (NUT) class of black hole having the event horizon \((\mathcal{H}^+)\) and the Cauchy horizon \((\mathcal{H}^-)\). Remarkably, we find that the \textit{mass parameter can be expressed as sum of three energies, i.e.,} \(M=\mathcal{E}_s^{\pm}+\mathcal{E}_r^{\pm}+\mathcal{E}_{em}^{\pm}\). It has been \textit{tested} for Taub-NUT black hole, Reissner-Nordström-Taub-NUT black hole, Kerr-Taub-NUT black hole and Kerr-Newman-Taub-NUT black hole. In each case of black hole, we find that \textit{the sum of these energies is equal to the Komar mass}. It is plausible only due to the introduction of new conserved charges i. e. \(J_N=M\,N\) (where \(M=m\) is the Komar mass and \(N=n\) is the gravitomagnetic charge), which is closely analogue to the Kerr-like angular momentum parameter \(J=a\,M\).Repulsive gravity effects in horizon formation. Horizon remnants in naked singularitieshttps://www.zbmath.org/1483.830612022-05-16T20:40:13.078697Z"Pugliese, Daniela"https://www.zbmath.org/authors/?q=ai:pugliese.daniela"Quevedo, Hernando"https://www.zbmath.org/authors/?q=ai:quevedo.hernandoSummary: Repulsive gravity is a well known characteristic of naked singularities. In this work, we explore light surfaces and find new effects of repulsive gravity. We compare Kerr naked singularities with the corresponding black hole counterparts and find certain structures that are identified as horizon remnants. We argue that these features might be significant for the comprehension of processes that lead to the formation or eventually destruction of black hole Killing horizons. These features can be detected by observing photon orbits, particularly close to the rotation axis, which can be used to distinguish naked singularities from black holes.Polytropic anti-de Sitter black holehttps://www.zbmath.org/1483.830622022-05-16T20:40:13.078697Z"Salti, M."https://www.zbmath.org/authors/?q=ai:salti.mustafa"Aydogdu, O."https://www.zbmath.org/authors/?q=ai:aydogdu.oktay"Sogut, K."https://www.zbmath.org/authors/?q=ai:sogut.kenanSummary: In the present study, we mainly discuss the features of polytropic anti-de Sitter (PAdS) black hole solution, which can be taken into account also as a stable configuration for dark energy stars. A dark energy star is a hypothetical compact astrophysical object and it has gained astrophysical relevance in literature for several reasons, for instance, it may be another interpretation for observations of astronomical black hole candidates. The idea basically points out that falling matter is transformed into dark energy (or vacuum energy), as the matter falls through the event horizon. In the first step of our investigation, assuming thermodynamical parameters of the asymptotically AdS black hole are identical to those introduced for the generalized polytropic gas, we obtain an exact solution for the metric function describing interior domain of the PAdS black hole. Then, we investigate the physical features of intermediate (shell) region. Subsequently, we describe physical properties like energy conditions and hydrostatic equilibrium via mathematical calculations as well as graphical analyses. In the final step, because black holes can be naturally regarded as a thermal device, we focus on a heat engine process for the PAdS black hole and obtain an analytical expression for the efficiency in terms of entropy and temperature.Geometrothermodynamics of black holes with a nonlinear sourcehttps://www.zbmath.org/1483.830632022-05-16T20:40:13.078697Z"Sánchez, Alberto"https://www.zbmath.org/authors/?q=ai:rivadulla-sanchez.albertoSummary: We study thermodynamics and geometrothermodynamics of a particular black hole configuration with a nonlinear source. We use the mass as fundamental equation, from which it follows that the curvature radius must be considered as a thermodynamic variable, leading to an extended equilibrium space. Using the formalism of geometrothermodynamics, we show that the geometric properties of the thermodynamic equilibrium space can be used to obtain information about thermodynamic interaction, critical points and phase transitions. We show that these results are compatible with the results obtained from classical black hole thermodynamics.Greybody factor for a rotating Bardeen black hole by perfect fluid dark matterhttps://www.zbmath.org/1483.830642022-05-16T20:40:13.078697Z"Sharif, M."https://www.zbmath.org/authors/?q=ai:sharif.muhammad-a-r|sharif.mhd-saeed|sharif.masoud"Shaukat, Sulaman"https://www.zbmath.org/authors/?q=ai:shaukat.sulamanSummary: In this paper, the greybody factor is studied analytically for a rotating regular Bardeen black hole surrounded by perfect fluid dark matter. Firstly, we examine the behavior of effective potential by using the radial equation of motion developed from the Klein-Gordon equation. We then consider tortoise coordinate to convert the radial equation into Schrödinger form equation. We solve the radial equation of motion and obtain two different asymptotic solutions in terms of hypergeometric function measured at distinct regimes so called near and far-field horizons. These solutions are smoothly matched over the whole radial coordinate in an intermediate regime to check their viability. Finally, we measure the absorption probability for massless scalar field and examine the effect of perfect fluid dark matter. It is concluded that both the effective potential and greybody factor increase with perfect fluid dark matter.Thermodynamics of a static electric-magnetic black hole in Einstein-Born-Infeld-AdS theory with different horizon geometrieshttps://www.zbmath.org/1483.830652022-05-16T20:40:13.078697Z"Tataryn, M. B."https://www.zbmath.org/authors/?q=ai:tataryn.m-b"Stetsko, M. M."https://www.zbmath.org/authors/?q=ai:stetsko.mykola-mSummary: We consider black hole solutions with electric and magnetic sources in the four-dimensional Einstein-Born-Infeld-AdS theory with spherical, planar and hyperbolic horizon geometries. Exact analytical solutions for the metric function, electric and magnetic fields were obtained and they recover the RN-AdS black hole in the limit \(\beta \rightarrow +\infty\) for spherical horizon in the absence of the magnetic charge. Expressions for temperature, electric and magnetic potential were obtained and they satisfy the first law of the extended black hole thermodynamics, where a negative cosmological constant is associated with thermodynamic pressure. Also, the Born-Infeld vacuum polarization term \(Bd\beta\) was included into the first law in order to satisfy the Smarr relation. Critical behavior of the black hole was examined and condition on electric and magnetic charges were obtained when phase transition appears. Also, the critical ratio and capacity at constant pressure were calculated. Electric and magnetic charges enter into the metric function and thermodynamic quantities symmetrically and thus the presence of the magnetic charge does not bring very significant new features. Finally, we examine the Joule-Thomson expansion if the black hole mass is fixed. The inversion and isenthalpic curves were plotted and the cooling and heating regions were demonstrated. These results recover the Joule-Thomson expansion recently considered for the RN-AdS black hole in the corresponding limit.Vaidya-Bonnor black hole in monopole-de Sitter space with variable \(\varLambda (u)\)https://www.zbmath.org/1483.830662022-05-16T20:40:13.078697Z"Vaiphei, ST Khaiminthang"https://www.zbmath.org/authors/?q=ai:vaiphei.st-khaiminthang"Ibohal, Ng."https://www.zbmath.org/authors/?q=ai:ibohal.ng"Singh, M. R."https://www.zbmath.org/authors/?q=ai:singh.maibam-ranjit|singh.medini-r|singh.mahi-r|singh.manas-ranjanSummary: In this paper, we propose a class of embedded solutions of Einstein's field equations with the de Sitter cosmological function \(\varLambda (u)\). This class of solutions describes Vaidya-Bonnor-monopole-de Sitter space-time with variable \(\varLambda (u)\). It may also be interpreted as Vaidya-Bonnor black hole in monopole-de Sitter space with variable \(\varLambda (u)\). It is shown the natural modification of Einstein's field equations with the de Sitter cosmological function \(\varLambda (u)\). In the energy-momentum tensor of the gravitational field in the embedded solution it is also seen the interaction of electromagnetic field with monopole and de Sitter fields having different equations of state parameters. It is
also established that the time like vector field of the matter distribution in the embedded space-time geometry is expanding, accelerating and shearing, but non-rotating. We have also discussed the areas, entropies, surface gravities and temperatures for the different horizons for the solution. From the embedded solution we may also recover possible solutions with variable \(\varLambda (u)\) such as (i) Vaidya-Bonnor-de Sitter, (ii) Vaidya-Bonnor-monopole, (iii) Vaidya-monopole, (iv) charged monopole-de Sitter and (v) uncharged monopole-de Sitter. From the study of these exact solutions, it is found that the physical properties of an embedded black hole are depended on the nature of the background spaces. It is also true in the case of the cosmological de Sitter space with variable \(\varLambda (u)\) that the charged monopole-de Sitter and the uncharged monopole-de Sitter spaces have different properties depending upon the charged spaces.Morris-Thorne wormholes in modified \(f(R, T)\) gravityhttps://www.zbmath.org/1483.830672022-05-16T20:40:13.078697Z"Chanda, A."https://www.zbmath.org/authors/?q=ai:chanda.anirban"Dey, S."https://www.zbmath.org/authors/?q=ai:dey.sagar"Paul, B. C."https://www.zbmath.org/authors/?q=ai:paul.bikash-chandraSummary: Wormhole solutions obtained by Morris and Thorne (MT) in general relativity (GR) is investigated in a modified theory of gravity. In the gravitational action, we consider \(f(R, T)\) which is a function of the Ricci scalar \((R)\) and the trace of the energy-momentum tensor \((T)\). In the framework of a modified gravity described by \(f(R,T)=R+\alpha R^2+\lambda T^{\beta}\), where \(\alpha , \beta\) and \(\lambda\) are coupling constants, MT wormhole (WH) solutions with normal matter are obtained for a relevant shape function. We have considered two different values of \(\beta\) leading to two forms of \(f(R, T)\)-gravity. The energy conditions are probed at the throat and away from the throat of the WH. It is found that the coupling parameters, \( \alpha\) and \(\lambda\) in the gravitational action play an important role in deciding the matter composition in the wormholes. It is found that for a given \(\lambda \), WH exists in the presence of exotic matter at the throat when \(\alpha <0\). It is demonstrated here that WH exists even without exotic matter for \(\alpha >0\) in the modified gravity. Two different shape functions are considered to obtain WH solutions that are permitted with or without exotic matter. It is noted that in a modified \(f(R, T)\) gravity MT WH is permitted with normal matter which is not possible in GR. It is demonstrated that a class of WH solutions exist with anisotropic fluid for \(\lambda \ne -8\pi\). However, for flat asymptotic regions with anisotropic fluids WH solutions cannot be realized when \(\lambda =-8\pi\). All the energy conditions are found consistent with the hybrid shape function indicating existence of WH even with normal matter for \(\lambda \rightarrow 0\).Can magnetogenesis driven by dynamo instabilities in chiral fermion plasmas, favor Einstein-Cartan AdS cosmology?https://www.zbmath.org/1483.830682022-05-16T20:40:13.078697Z"de Andrade, L. C. Garcia"https://www.zbmath.org/authors/?q=ai:garcia-de-andrade.l-cSummary: In this letter we show that the magnetic field (MF) bounds induced by Einstein-Cartan-de Sitter (EC) with AdS anti-de Sitter spacetime geometry and fermionic torsion with chiral dynamo plasmas instabilities, with inhomogeneous uniform chiral chemical potential, indicates that there is a possibility, as far as magnetogenesis is concerned, that we may obtain more stringent results within ECAdS gravity, compared with general relativity (GR) limits obtained by Tsagas using torsionless magnetogenesis. Spinorial fermionic source with torsion induces a chiral plasmas oscillation. The time dependent chiral chemical potential, sometimes associated formally with torsion, [the author, ``Metric-torsion decay of non-adiabatic chiral helical magnetic fields against chiral dynamo action in bouncing cosmological models'', Eur. Phys. J. C, Part. Fields 78, No. 6, Paper No. 530, 7 p. (2018; \url{doi:10.1140/epjc/s10052-018-5983-x})], is obtained from chiral flipping equation. The MFs obtained from the present universe ECdS chiral dynamo model, meet the criteria of galactic seed fields with better limits within Tsagas range [\textit{C. G. Tsagas}, ``Relaxing the limits on inflationary magnetogenesis'', Phys. Rev. D (3) 92, No. 10--15, Article ID 101301, 5 p. (2015; \url{doi:10.1103/PhysRevD.92.101301})] seed galactic magnetic fields for dynamo mechanisms, than the bound obtained by chiral dynamos in torsionless AdS cosmology. Majorana neutrinos are used as spatial components of axial spin-torsion source of dynamo instability from neutrino asymmetry.Lifshitz scaling effects on the holographic paramagnetic-ferromagnetic phase transitionhttps://www.zbmath.org/1483.830692022-05-16T20:40:13.078697Z"Ghotbabadi, B. Binaei"https://www.zbmath.org/authors/?q=ai:ghotbabadi.b-binaei"Sheykhi, A."https://www.zbmath.org/authors/?q=ai:sheykhi.ahmad"Bordbar, G. H."https://www.zbmath.org/authors/?q=ai:bordbar.g-hSummary: We disclose the effects of Lifshitz dynamical exponent \(z\) on the properties of holographic paramagnetic-ferromagnetic phase transition in the background of Lifshitz spacetime. To preserve the conformal invariance in higher dimensions, we consider the Power-Maxwell (PM) electrodynamics as our gauge field. We introduce a massive 2-form coupled to the PM field and perform the numerical shooting method in the probe limit by assuming the PM and the 2-form fields do not back-react on the background geometry. The obtained results indicate that the critical temperature decreases with increasing the strength of the power parameter \(q\) and dynamical exponent \(z\). Besides, the formation of the magnetic moment in the black hole background is harder in the absence of an external magnetic field. At low temperatures, and in the absence of an external magnetic field, our result show the spontaneous magnetization and the ferromagnetic phase transition. We find that the critical exponent takes the universal value \(\beta=1/2\) regardless of the parameters \(q, z, d\), which is in agreement with the mean field theory. In the presence of an external magnetic field, the magnetic susceptibility satisfies the Curie-Weiss law.Covariant Hamiltonian formalism for \(F(R)\)-gravityhttps://www.zbmath.org/1483.830702022-05-16T20:40:13.078697Z"Klusoň, J."https://www.zbmath.org/authors/?q=ai:kluson.josef"Matouš, B."https://www.zbmath.org/authors/?q=ai:matous.bSummary: In this short note we apply Weyl-De Donder formalism, also known as covariant Hamiltonian formalism, for \(F(R)\)-gravity. We derive covariant Hamiltonian and derive corresponding equations of motion.Constraint on the equation of state parameter (\(\omega\)) in non-minimally coupled \(f(Q)\) gravityhttps://www.zbmath.org/1483.830712022-05-16T20:40:13.078697Z"Mandal, Sanjay"https://www.zbmath.org/authors/?q=ai:mandal.sanjay-kumar"Sahoo, P. K."https://www.zbmath.org/authors/?q=ai:sahoo.pradyumn-kumarSummary: We study observational constraints on the modified symmetric teleparallel gravity, the non-metricity \(f(Q)\) gravity, which reproduces background expansion of the universe. For this purpose, we use Hubble measurements, Baryonic Acoustic Oscillations (BAO), 1048 Pantheon supernovae type Ia data sample which integrate SuperNova Legacy Survey (SNLS), Sloan Digital Sky Survey (SDSS), Hubble Space Telescope (HST) survey, Panoramic Survey Telescope and Rapid Response System (Pan-STARRS1). We confront our cosmological model against observational samples to set constraints on the parameters using Markov Chain Monte Carlo (MCMC) methods. We find the equation of state parameter \(\omega = -0.853_{-0.020}^{+0.015}\) and \(\omega = -0.796_{-0.074}^{+0.049}\) for Hubble and Pantheon samples, respectively. As a result, the \(f(Q)\) model shows the quintessence behavior and deviates from \(\Lambda\)CDM.Holographic superconductors in 4D Einstein-Gauss-Bonnet gravity with backreactionshttps://www.zbmath.org/1483.830722022-05-16T20:40:13.078697Z"Pan, Jie"https://www.zbmath.org/authors/?q=ai:pan.jie"Qiao, Xiongying"https://www.zbmath.org/authors/?q=ai:qiao.xiongying"Wang, Dong"https://www.zbmath.org/authors/?q=ai:wang.dong.7|wang.dong|wang.dong.3|wang.dong.8|wang.dong.2|wang.dong.4|wang.dong.1|wang.dong.6|wang.dong.5"Pan, Qiyuan"https://www.zbmath.org/authors/?q=ai:pan.qiyuan"Nie, Zhang-Yu"https://www.zbmath.org/authors/?q=ai:nie.zhang-yu"Jing, Jiliang"https://www.zbmath.org/authors/?q=ai:jing.jiliangSummary: We construct the holographic superconductors away from the probe limit in the consistent \(D \to 4\) Einstein-Gauss-Bonnet gravity. We observe that, both for the ground state and excited states, the critical temperature first decreases then increases as the curvature correction tends towards the Chern-Simons limit in a backreaction dependent fashion. However, the decrease of the backreaction, the increase of the scalar mass, or the increase of the number of nodes will weaken this subtle effect of the curvature correction. Moreover, for the curvature correction approaching the Chern-Simons limit, we find that the gap frequency \(\omega_g/T_c\) of the conductivity decreases first and then increases when the backreaction increases in a scalar mass dependent fashion, which is different from the finding in the \((3 + 1)\)-dimensional superconductors that increasing backreaction increases \(\omega_g/T_c\) in the full parameter space. The combination of the Gauss-Bonnet gravity and backreaction provides richer physics in the scalar condensates and conductivity in the \((2 + 1)\)-dimensional superconductors.Rotational superradiance with Bogoliubov dispersionhttps://www.zbmath.org/1483.830732022-05-16T20:40:13.078697Z"Patrick, Sam"https://www.zbmath.org/authors/?q=ai:patrick.samThe article is of interest in spite of very different topics put into discussion, including astrophysical black holes, their modeling in analogue gravity up to Bose-Einstein condensates in solid state physics. The puropse of the author was to show that the dispersion relation found by \textit{N. N. Bogolyubov} and published in [Acad. Sci. USSR, J. Phys. 11 (1947)], would lead to a some decrease of the effect of superradiaton. The effect of superradiation in black holes physics came to interest since 1971. It consists in the amplification of falling spin-integer waves and mass fields by Kerr (rotating) Black Holes, if a suitable condition relating the frequency of the incident wave and the angular frequency of a Black Hole is fulfilled. From an other hand, the effect of superradiance can take place also in Bose-Einstein condensates in solids.
See, for example the articles by \textit{N. N. Bogolubov jun.} et al. [Int. J. Mod. Phys. B 1, No. 1, 69--88 (1987; Zbl 1165.82313)], which represents an English version of the lecture, published in: Quantum processes in intensive fields [Kishinev Izdatel Shtiintsa. 45--54 (1987)] and a continuation of the research by the same authors published in ICTP preprint: IC/84/214, which relates directly with experiment. The article is of undoubtible interest.
Meanwhile, I have some bibliographical additions. Obviously, great effects come to mind concommitantly to many peoples. The pioneering work in the area of superradiation of waves by Black holes is by \textit{Y. B. Zeldovich} [Zh. Exp. Teor. Fiz., Pis' ma 14, 270 (1971)], developed in detail in [Sov. Phys. JETP 35, 1085 (1972)]. For mass scalar fields the superradiaion was investigated by \textit{Th. Damour} et al. in [Lett. Nuov. Cim. 15, No. 8, 257--262 (1976; \url{doi:10.1007/BF02725534})] in the JWKB approximation and by \textit{I. M. Ternov} et al. [Sov. Phys. J. 21, No. 9, 1200--1204 (1978; Zbl 1043.83544); translation from Izv. Vyssh. Uchebn. Zaved., Fiz. 21, No. 9, 109--114 (1978)] by exact solutions of the radial equation. The resulting Bose instability of Kerr Black holes due to mass fields was put into discussion by \textit{T. J. M. Zouros} and \textit{D. Eardley} in [Ann. Phys. (USA) 118, 139--155 (1979; \url{doi:10.1016/0003-4916(79)90237-9})]. A possible formation of Bose condensate in the field of Black Holes was suggested by the author of the review in [Sov. Astron. Lett. 15, No. 3, 243 (1989)].
Reviewer: Alex B. Gaina (Chişinău)Wave packet treatment of neutrino flavor oscillations in various spacetimeshttps://www.zbmath.org/1483.830742022-05-16T20:40:13.078697Z"Sadeghi, P."https://www.zbmath.org/authors/?q=ai:sadeghi.parvin|sadeghi.parastoo"Hammad, F."https://www.zbmath.org/authors/?q=ai:hammad.faycal"Landry, A."https://www.zbmath.org/authors/?q=ai:landry.anthony"Martel, T."https://www.zbmath.org/authors/?q=ai:martel.tSummary: We study the effect of gravity on neutrino flavor oscillations when each mass eigenstate is described by a wave packet instead of a plane wave. Two different approaches for implementing the wave packet formalism in the study of neutrino flavor oscillations in curved spacetime are examined. We work with a general static and spherically symmetric spacetime before applying our results to a few spacetime metrics of interest. We first focus on general relativity by examining the effect of the exterior and interior Schwarzschild solutions, as well as the de Sitter-Schwarzschild metric, and then we examine selected metrics from modified gravity models.Gauge field theory vacuum and cosmological inflation without scalar fieldhttps://www.zbmath.org/1483.830752022-05-16T20:40:13.078697Z"Savvidy, George"https://www.zbmath.org/authors/?q=ai:savvidy.george-kSummary: We derive the quantum energy-momentum tensor and the corresponding quantum equation of state for gauge field theory using the effective Lagrangian approach. The energy-momentum tensor has a term proportional to the space-time metric and provides a finite non-diverging contribution to the effective cosmological term. This allows to investigate the influence of the gauge field theory vacuum polarisation on the evolution of Friedmann cosmology, inflation and primordial gravitational waves. The Type I-IV solutions of the Friedmann equations induced by the gauge field theory vacuum polarisation provide an alternative inflationary mechanism and a possibility for late-time acceleration. The Type II solution of the Friedmann equations generates the initial exponential expansion of the universe of finite duration and the Type IV solution demonstrates late-time acceleration. The solutions fulfil the necessary conditions for the amplification of primordial gravitational waves.The emergence of expanding space-time and intersecting D-branes from classical solutions in the Lorentzian type IIB matrix modelhttps://www.zbmath.org/1483.830762022-05-16T20:40:13.078697Z"Hatakeyama, Kohta"https://www.zbmath.org/authors/?q=ai:hatakeyama.kohta"Matsumoto, Akira"https://www.zbmath.org/authors/?q=ai:matsumoto.akira"Nishimura, Jun"https://www.zbmath.org/authors/?q=ai:nishimura.jun-ichi"Tsuchiya, Asato"https://www.zbmath.org/authors/?q=ai:tsuchiya.asato"Yosprakob, Atis"https://www.zbmath.org/authors/?q=ai:yosprakob.atisSummary: The type IIB matrix model is a promising candidate for a nonperturbative formulation of superstring theory. As such, it is expected to explain the origin of space-time and matter at the same time. This has been partially demonstrated by the previous Monte Carlo studies on the Lorentzian version of the model, which suggested the emergence of (3+1)-dimensional expanding space-time. Here we investigate the same model by solving numerically the classical equation of motion, which is expected to be valid at late times since the action becomes large due to the expansion of space. Many solutions are obtained by the gradient descent method starting from random matrix configurations, assuming a quasi-direct-product structure for the (3+1)-dimensions and the extra 6 dimensions. We find that these solutions generally admit the emergence of expanding space-time and a block-diagonal structure in the extra dimensions, the latter being important for the emergence of intersecting D-branes. For solutions corresponding to D-branes with appropriate dimensionality, the Dirac operator is shown to acquire a zero mode in the limit of infinite matrix size.Straightforward Hamiltonian analysis of \textit{BF} gravity in \(n\) dimensionshttps://www.zbmath.org/1483.830772022-05-16T20:40:13.078697Z"Montesinos, Merced"https://www.zbmath.org/authors/?q=ai:montesinos.merced"Escobedo, Ricardo"https://www.zbmath.org/authors/?q=ai:escobedo.ricardo"Celada, Mariano"https://www.zbmath.org/authors/?q=ai:celada.marianoSummary: We perform, in a manifestly \(\mathrm{SO}(n-1,1) [\mathrm{SO}(n)]\) covariant fashion, the Hamiltonian analysis of general relativity in \(n\) dimensions written as a constrained \textit{BF} theory. We solve the constraint on the \(B\) field in a way naturally adapted to the foliation of the spacetime that avoids explicitly the introduction of the vielbein. This leads to a form of the action involving a presymplectic structure, which is reduced by doing a suitable parametrization of the connection and then, after integrating out some auxiliary fields, the Hamiltonian form involving only first-class constraints is obtained.Universal mass scale for bosonic fields in multi-brane worldshttps://www.zbmath.org/1483.830782022-05-16T20:40:13.078697Z"de Oliveira Junior, R. I."https://www.zbmath.org/authors/?q=ai:de-oliveira.r-i-jun"Alencar, G."https://www.zbmath.org/authors/?q=ai:alencar.geovaSummary: In this paper we find an universal mass scale for all \(q\)-forms in multi-brane worlds model. It is known that this model provides an ultralight mode for the fields. However, to get this, the Lagrangians considered in the literature are not covariant. In order to solve this, we propose a covariant version to multi-localize \(q\)-form fields. As a consequence of the covariance, we show that all the \(q\)-form fields have an ultralight mode with the same mass as the gravitational one. That way we show that there is an universal mass scale for the ultralight modes of the bosonic fields. This suggests that a new physics must emerge, for all these fields, at the same scale.An algebraic classification of solution generating techniqueshttps://www.zbmath.org/1483.830792022-05-16T20:40:13.078697Z"Borsato, Riccardo"https://www.zbmath.org/authors/?q=ai:borsato.riccardo"Driezen, Sibylle"https://www.zbmath.org/authors/?q=ai:driezen.sibylle"Hassler, Falk"https://www.zbmath.org/authors/?q=ai:hassler.falkSummary: We consider a two-fold problem: on the one hand, the classification of a family of solution-generating techniques in (modified) supergravity and, on the other hand, the classification of a family of canonical transformations of 2-dimensional \(\sigma \)-models giving rise to integrable-preserving transformations. Assuming a generalised Scherk-Schwarz ansatz, in fact, the two problems admit essentially the same algebraic formulation, emerging from an underlying double Lie algebra \(\mathfrak{d}\). After presenting our derivation of the classification, we discuss in detail the relation to modified supergravity and the additional conditions to recover the standard (unmodified) supergravity. Starting from our master equation -- that encodes all the possible continuous deformations allowed in the family of solution-generating techniques -- we show that these are classified by the Lie algebra cohomologies \(H^2(\mathfrak{h}, \mathbb{R})\) and \(H^3(\mathfrak{h}, \mathbb{R})\) of the maximally isotropic subalgebra \(\mathfrak{h}\) of the double Lie algebra \(\mathfrak{d} \). We illustrate our results with a non-trivial example, the bi-Yang-Baxter-Wess-Zumino model.Gravitino condensate in \(N = 1\) supergravity coupled to the \(N = 1\) supersymmetric Born-Infeld theoryhttps://www.zbmath.org/1483.830802022-05-16T20:40:13.078697Z"Ishikawa, Ryotaro"https://www.zbmath.org/authors/?q=ai:ishikawa.ryotaro"Ketov, Sergei V."https://www.zbmath.org/authors/?q=ai:ketov.sergei-vSummary: The \(N=1\) supersymmetric Born-Infeld theory coupled to \(N=1\) supergravity in four spacetime dimensions is studied in the presence of a cosmological term with spontaneous supersymmetry breaking. The consistency is achieved by compensating a negative contribution to the cosmological term from the Born-Infeld theory by a positive contribution originating from the gravitino condensate. This leads to an identification of the Born-Infeld scale with the supersymmetry-breaking scale. The dynamical formation of the gravitino condensate in supergravity is reconsidered and the induced one-loop effective potential is derived. Slow-roll cosmological inflation with the gravitino condensate as the inflaton (near the maximum of the effective potential) is viable against the Planck 2018 data and can lead to the inflationary (Hubble) scale as high as \(10^{12}\) GeV. Uplifting the Minkowski vacuum (after inflation) to a de Sitter vacuum (dark energy) is possible by the use of the alternative Fayet-Iliopoulos term. Some major physical consequences of our scenario for reheating are also briefly discussed.Electrostatic description of five-dimensional SCFTshttps://www.zbmath.org/1483.830812022-05-16T20:40:13.078697Z"Legramandi, Andrea"https://www.zbmath.org/authors/?q=ai:legramandi.andrea"Nunez, Carlos"https://www.zbmath.org/authors/?q=ai:nunez.carlosSummary: In this paper we discuss an infinite class of \(\mathrm{AdS}_6\) backgrounds in Type IIB supergravity dual to five dimensional SCFTs whose low energy description is in terms of linear quiver theories. The quantisation of the Page charges imposes that each solution is determined once a convex, piece-wise linear function is specified. In the dual field theory, we interpret this function as encoding the ranks of colour and flavour groups in the associated quiver. We check our proposal with several examples and provide general expressions for the holographic central charge and the Wilson loop VEV. Some solutions outside this general class, with less clear quiver interpretation, are also discussed.The unified history of the viscous accelerating universe and phase transitionshttps://www.zbmath.org/1483.830822022-05-16T20:40:13.078697Z"Astashenok, A. V."https://www.zbmath.org/authors/?q=ai:astashenok.artyom-v"Odintsov, S. D."https://www.zbmath.org/authors/?q=ai:odintsov.sergei-d"Tepliakov, A. S."https://www.zbmath.org/authors/?q=ai:tepliakov.a-sSummary: We propose the unified description of the early acceleration (cosmological inflation) and the present epoch of so called ``dark energy''. The inflation can be described by cosmic fluid with van der Waals equation of state and with viscosity term. Viscosity leads to slow-roll inflation with the parameters such as the spectral index, and the tensor-to-scalar ratio in concordance with observational data. Our next step is to modify this equation of state (EoS) to describe the present accelerated expansion. One can add the term into EoS so that the contribution of which is small for inflation but crucial for late-time acceleration. The key point of the model is possible phase transition which leads to decrease of the viscosity. We show that proposed model describes observational data about standard ``candles'' and correct dependence of Hubble parameter from redshift. Moreover, we propose the possible scenario to resolve dark matter problem.Inflation, phase transitions and the cosmological constanthttps://www.zbmath.org/1483.830832022-05-16T20:40:13.078697Z"Bertolami, Orfeu"https://www.zbmath.org/authors/?q=ai:bertolami.orfeuSummary: Cosmological phase transitions are thought to have taken place at the early Universe imprinting their properties on the observable Universe. There is strong evidence that, through the dynamics of a scalar field that lead a second order phase transition, inflation shaped the Universe accounting for the most conspicuous features of the observed Universe. It is argued that inflation has also striking implications for the vacuum energy. Considerations for subsequent second order phase transitions are also discussed.Cosmological implications of the hydrodynamical phase of group field theoryhttps://www.zbmath.org/1483.830842022-05-16T20:40:13.078697Z"Gabbanelli, Luciano"https://www.zbmath.org/authors/?q=ai:gabbanelli.luciano"De Bianchi, Silvia"https://www.zbmath.org/authors/?q=ai:de-bianchi.silviaSummary: In this review we focus on the main cosmological implications of the Group Field Theory approach, according to which an effective continuum macroscopic dynamics can be extracted from the underlying formalism for quantum gravity. Within this picture what counts is the collective behaviour of a large number of quanta of geometry. The resulting state is a condensate-like structure made of ``pre-geometric'' excitations of the Group Field Theory field over a no-space vacuum. Starting from the kinematics and dynamics, we offer an overview of the way in which Group Field Theory condensate cosmology treats solutions for the homogeneous and isotropic universe. These solutions including a bounce, share with other quantum cosmological approaches the resolution of the singularity characterizing general relativity. Contrary to what is usually done in quantum cosmology, in Group Field Theory cosmology no preliminary symmetry reduction is needed for this purpose. We conclude with a discussion of the limits and future perspectives of the Group Field Theory approach.Noether symmetry in Newtonian dynamics and cosmologyhttps://www.zbmath.org/1483.830852022-05-16T20:40:13.078697Z"Guendelman, E. I."https://www.zbmath.org/authors/?q=ai:guendelman.eduardo-i"Zamlung, E."https://www.zbmath.org/authors/?q=ai:zamlung.e"Benisty, D."https://www.zbmath.org/authors/?q=ai:benisty.davidSummary: A new symmetry for Newtonian Dynamics is analyzed, this corresponds to going to an accelerated frame, which introduces a constant gravitational field into the system and subsequently. We consider the addition of a linear contribution to the gravitational potential \(\phi\) which can be used to cancel the gravitational field induced by going to the accelerated from, the combination of these two operations produces then a symmetry. This symmetry leads then to a Noether current which is conserved. The conserved charges are analyzed in special cases. The charges may not be conserved if the Noether current produces flux at infinity, but such flux can be eliminated by going to the CM (center of mass) system in the case of an isolated system. In the CM frame the Noether charge vanishes, Then we study connection between the Cosmological Principle and the Newtonian Dynamics which was formulated via a symmetry \textit{D. Benisty} and \textit{E. I. Guendelman} [Mod. Phys. Lett. A 35, No. 16, Article ID 2050131, 7 p. (2020; Zbl 1435.85006)] of this type, but without an action formulation. Homogeneous behavior for the coordinate system relevant to cosmology leads to a zero Noether current and the requirement of the Newtonian potential to be invariant under the symmetry in this case yields the Friedmann equations, which appear as a consistency condition for the symmetry.Solar system, astrophysics, and cosmology from the derivative expansionhttps://www.zbmath.org/1483.830862022-05-16T20:40:13.078697Z"Haddad, Nidal"https://www.zbmath.org/authors/?q=ai:haddad.nidal"Haddad, Fateen"https://www.zbmath.org/authors/?q=ai:haddad.fateenSummary: In this paper we show how the solar system, the galactic, and the cosmological scales, are accommodated in a single framework, namely, in the derivative expansion framework. We construct a locally inertial static metric, based on the Einstein equations and on the derivative expansion method, which describes a Schwarzschild black hole immersed in dark matter and dark energy. The leading order metric in the expansion corresponds to the solar system, the first order metric to the galaxy, and the second order metric to cosmology. It is shown how this metric captures the main observations at each scale: in the solar system it trivially gives the Keplerian physics, in the galaxy it gives the flat part of the rotation curve and the Baryonic Tully-Fisher relation, and in the cosmological scale it gives the cosmological redshift, the accelerating expansion, and it coincides with the Robertson-Walker spacetime in the appropriate limit and approximation.Magnetogenesis in Higgs inflationhttps://www.zbmath.org/1483.830872022-05-16T20:40:13.078697Z"Kamarpour, Mehran"https://www.zbmath.org/authors/?q=ai:kamarpour.mehranSummary: We study the generation of magnetic fields in the Higgs inflation model with the axial coupling in order to break the conformal invariance of the Maxwell action and produce strong enough magnetic fields for observed large-scale magnetic fields. This interaction breaks the parity and enables a production of only one of the polarization states of the electromagnetic field due to axion-like coupling of electromagnetic field to the inflation. Therefore, the produced magnetic fields are helical. In fact, calculations show the mode of one polarization undergoes amplification, while the other one diminishes. We consider radiatively corrected Higgs inflation potential. In comparison to the Starobinsky potential, we obtain an extra term as a one loop correction and determine the spectrum of generalized electromagnetic fields. The effect of quantum correction modifies potential so that in some certain conditions when
back reaction is weak the observed large-scale magnetic field can be explained by our modified potential. We should emphasize in this model we only consider linear approximation for electromagnetic field so that the theory does not contain higher-order derivatives and the so-called ghost degrees of freedom. Therefore, the theory is consistent with cosmology. In addition, the magnetic field generated in this model has very small correlation length. It is impossible to explain within this model both the strength of magnetic field and its large coherence length. Due to the nontrivial helicity, the produced magnetic fields undergo the inverse cascade process in the turbulent plasma which can strongly increase their correlation length. We find that, for two values of coupling parameter \(\chi_1=5\times 10^9M_p^{-2}\) and \(\chi_1=7.5\times 10^9M_p^{-2}\), the back-reaction is weak and our analysis is valid.Nonstaticity with type II, III, or IV matter field in \(f(R_{\mu\nu\rho\sigma},g^{\mu\nu})\) gravityhttps://www.zbmath.org/1483.830882022-05-16T20:40:13.078697Z"Maeda, Hideki"https://www.zbmath.org/authors/?q=ai:maeda.hidekiSummary: In all \(n(\ge 3)\)-dimensional gravitation theories whose Lagrangians are functions of the Riemann tensor and metric, we show that static solutions are absent unless the total energy-momentum tensor for matter fields is of type I in the Hawking-Ellis classification. In other words, there is no hypersurface-orthogonal timelike Killing vector in a spacetime region with an energy-momentum tensor of type II, III, or IV. This asserts that, if back-reaction is taken into account to give a self-consistent solution, ultra-dense regions with a semiclassical type-IV matter field cannot be static even with higher-curvature correction terms. As a consequence, a static Planck-mass relic is possible as a final state of an evaporating black hole only if the semiclassical total energy-momentum tensor is of type I.Static cosmological solutions in quadratic gravityhttps://www.zbmath.org/1483.830892022-05-16T20:40:13.078697Z"Müller, Daniel"https://www.zbmath.org/authors/?q=ai:muller.daniel"Toporensky, Alexey"https://www.zbmath.org/authors/?q=ai:toporensky.alexey-vSummary: We consider conditions for existence and stability of a static cosmological solution in quadratic gravity. It appears that such a solution for a Universe filled by only one type of perfect fluid is possible in a wide range of the equation of state parameter \(w\) and for both positively and negatively spatially curved Universe. We show that the static solution for the negative curvature is always unstable if we require positive energy density of the matter content. On the other hand, a static solution with positive spatial curvature can be stable under certain restrictions. Stability of this solution with respect to isotropic perturbation requires that the coupling constant with the \(R^2\) therm in the Lagrangian of the theory is positive, and the equations of state parameter \(w\) is located in a rather narrow interval. Nevertheless, the stability condition does not require violation of the strong energy condition. Taking into account anisotropic perturbations leads to further restrictions on the values of coupling constants and the parameter \(w\).Pre-inflationary bounce effects on primordial gravitational waves of \(f(R)\) gravityhttps://www.zbmath.org/1483.830902022-05-16T20:40:13.078697Z"Odintsov, S. D."https://www.zbmath.org/authors/?q=ai:odintsov.sergei-d"Oikonomou, V. K."https://www.zbmath.org/authors/?q=ai:oikonomou.vasilis-kSummary: In this work we shall study a possible pre-inflationary scenario for our Universe and how this might be realized by \(f(R)\) gravity. Specifically, we shall introduce a scenario in which the Universe in the pre-inflationary era contracts until it reaches a minimum magnitude, and subsequently expands, slowly entering a slow-roll quasi-de Sitter inflationary era. This pre-inflationary bounce avoids the cosmic singularity, and for the eras before and after the quasi-de Sitter inflationary stage, approximately satisfies the string theory motivated scale factor duality \(a(t) = a^{-1}(-t)\).
We investigate which approximate forms of \(f(R)\) can realize such a non-singular pre-inflationary scenario, the quasi-de Sitter patch of which is described by an \(R^2\) gravity, thus the exit from inflation is guaranteed. Furthermore, since in string theory pre-Big Bang scenarios lead to an overall amplification of the gravitational wave energy spectrum, we examine in detail this perspective for the \(f(R)\) gravity generating this pre-inflationary non-singular bounce. As we show, in the \(f(R)\) gravity case, the energy spectrum of the primordial gravitational waves background is also amplified, however the drawback is that the amplification is too small to be detected by future high frequency interferometers. Thus we conclude that, as in the case of single scalar field theories, \(f(R)\) gravity cannot produce detectable stochastic gravitational waves and a synergistic theory of scalars and higher order curvature terms might be needed.Particle creation in some LRS Bianchi I modelshttps://www.zbmath.org/1483.830912022-05-16T20:40:13.078697Z"Pimentel, Luis O."https://www.zbmath.org/authors/?q=ai:pimentel.luis-o"Pineda, Flavio"https://www.zbmath.org/authors/?q=ai:pineda.flavioSummary: In this work we consider particle creation by the expansion of the universe, using two Bianchi type I anisotropic models. The particles studied are of spin 0 and 1/2. The cosmological models have rotational symmetry, which allows us to solve exactly the equations of motion. The number density of the created particles is calculated with the method of Bogolubov transformations.On cosmological expansion and local physicshttps://www.zbmath.org/1483.830922022-05-16T20:40:13.078697Z"Pons, J. M."https://www.zbmath.org/authors/?q=ai:pons.josep-m"Talavera, P."https://www.zbmath.org/authors/?q=ai:talavera.pereSummary: We find an exact convergence in the local dynamics described by two supposedly antagonistic approaches applied at the local, solar system scale: one starting from an expanding universe perspective such as FLRW, the other based on a local model ignoring any notion of expansion, such as static Schwarzschild dS. Both models are in complete agreement when the local effects of the expansion are circumscribed to the presence of the cosmological constant. We elaborate on the relevant role of static backgrounds like the Schwarzschild-dS metric in standard form as the most proper coordinatizations to describe physics at the local scale. We also elaborate on the popular expanding 3-space picture -- to be distinguished from that of the expanding universe -- and point out the confusion of scales which is typically associated with it. Finally, making use of an old and too often forgotten relativistic kinematical invariant, we address some remaining misunderstandings on space expansion, cosmological and gravitational redshifts. As a byproduct we propose a \textit{unique and unambiguous} prescription to match the local and cosmological expression of a specific observable.Interaction rates in cosmology: heavy particle production and scatteringhttps://www.zbmath.org/1483.830932022-05-16T20:40:13.078697Z"Rai, Mudit"https://www.zbmath.org/authors/?q=ai:rai.mudit"Boyanovsky, Daniel"https://www.zbmath.org/authors/?q=ai:boyanovsky.danielNon-singular non-flat universeshttps://www.zbmath.org/1483.830942022-05-16T20:40:13.078697Z"Salamanca, Andrés Felipe Estupiñán"https://www.zbmath.org/authors/?q=ai:salamanca.andres-felipe-estupinan"Medina, Sergio Bravo"https://www.zbmath.org/authors/?q=ai:bravo-medina.sergio"Nowakowski, Marek"https://www.zbmath.org/authors/?q=ai:nowakowski.marek"Batic, Davide"https://www.zbmath.org/authors/?q=ai:batic.davideSummary: The quest to understand better the nature of the initial cosmological singularity is with us since the discovery of the expanding universe. Here, we propose several non-flat models, among them the standard cosmological scenario with a critical cosmological constant, the Einstein-Cartan cosmology, the Milne-McCrea universe with quantum corrections and a non-flat universe with bulk viscosity. Within these models, we probe into the initial singularity by using different techniques. Several nonsingular universes emerge, one of the possibilities being a static non-expanding and stable Einstein universe.Oscillons during Dirac-Born-Infeld preheatinghttps://www.zbmath.org/1483.830952022-05-16T20:40:13.078697Z"Sang, Yu"https://www.zbmath.org/authors/?q=ai:sang.yu"Huang, Qing-Guo"https://www.zbmath.org/authors/?q=ai:huang.qingguoSummary: Oscillons are long-lived, localized, oscillating nonlinear excitations of a real scalar field which can be abundantly produced during preheating after inflation. We give the first \((3 + 1)\)-dimensional simulation for the oscillon formation during preheating with noncanonical kinetic terms, e.g. the Dirac-Born-Infeld form, and find that the formation of oscillons is significantly influenced by the noncanonical effect.On gravitational Stefan-Boltzmann law and Casimir effect in FRW universehttps://www.zbmath.org/1483.830962022-05-16T20:40:13.078697Z"Santos, A. F."https://www.zbmath.org/authors/?q=ai:santos.alesandro-ferreira"Ulhoa, S. C."https://www.zbmath.org/authors/?q=ai:ulhoa.sergio-c"Spaniol, E. P."https://www.zbmath.org/authors/?q=ai:spaniol.e-p"Khanna, Faqir C."https://www.zbmath.org/authors/?q=ai:khanna.faqir-cSummary: Both Stefan-Boltzmann law and the Casimir effect, in a universe described by the FRW metric with zero curvature, are calculated. These effects are described by Thermo Field Dynamics (TFD). The gravitational energy-momentum tensor is defined in the context of Teleparallel Equivalent to General Relativity (TEGR). Each of the two effects gives a consistent prediction with what is observed on a cosmological scale. One of the effect establishes a minimum range for the deceleration parameter. While another leads to the conclusion that a possible cosmological constant has a very small order of magnitude.Inflation with Gauss-Bonnet and Chern-Simons higher-curvature-corrections in the view of GW170817https://www.zbmath.org/1483.830972022-05-16T20:40:13.078697Z"Venikoudis, S. A."https://www.zbmath.org/authors/?q=ai:venikoudis.s-a"Fronimos, F. P."https://www.zbmath.org/authors/?q=ai:fronimos.f-pSummary: Inflationary era of our Universe can be characterized as semi-classical because it can be described in the context of four-dimensional Einstein's gravity involving quantum corrections. These string motivated corrections originate from quantum theories of gravity such as superstring theories and include higher gravitational terms as, Gauss-Bonnet and Chern-Simons terms. In this paper we investigated inflationary phenomenology coming from a scalar field, with quadratic curvature terms in the view of GW170817. Firstly, we derived the equations of motion, directly from the gravitational action. As a result, formed a system of
differential equations with respect to Hubble's parameter and the inflaton field which was very complicated and cannot be solved analytically, even in the minimal coupling case. Based on the observations from GW170817 event, which have shown that the speed of the primordial gravitational wave is equal to the speed of light, \(c_{\mathcal{T}}^2=1\) in natural units, our equations of motion where simplified after applying the constraint \(c_{\mathcal{T}}^2=1\), the slow-roll approximations and neglecting the string corrections. We described the dynamics of inflationary phenomenology and proved that theories with Gauss-Bonnet term can be compatible with recent observations. Also, the Chern-Simons term leads to asymmetric generation and evolution of the two circular polarization states of gravitational wave. Finally, viable inflationary models are presented, consistent with the observational constraints. The possibility of a blue tilted tensor spectral index is briefly investigated.Quantum phase space description of a cosmological minimal massive bigravity modelhttps://www.zbmath.org/1483.830982022-05-16T20:40:13.078697Z"Vera-Hernández, Julio César"https://www.zbmath.org/authors/?q=ai:vera-hernandez.julio-cesarSummary: Bimetric gravity theories describes gravitational interactions in the presence of an extra spin-2 field. The Hassan-Rosen (HR) nonlinear massive minimal bigravity theory is a ghost-free bimetric theory formulated with respect a flat, dynamical reference metric. In this work the deformation quantization formalism is applied to a HR cosmological model in the minisuperspace. The quantization procedure is performed explicitly for quantum cosmology in the minisuperspace. The Friedmann-Lemaître-Robertson-Walker model with flat metrics is worked out and the computation of the Wigner functions for the Hartle-Hawking, Vilenkin and Linde wavefunctions are done numerically and, in the Hartle-Hawking case, also analytically. From the stability analysis in the quantum minisuper phase space it is found an interpretation of the mass of graviton as an emergent cosmological constant and as a measure of the deviation of classical behavior of the Wigner functions. Also, from the Hartle-Hawking case, an interesting relation between the curvature and the mass of graviton in a cusp catastrophe surface is discussed.The evolution of binary neutron star post-merger remnants: a reviewhttps://www.zbmath.org/1483.850012022-05-16T20:40:13.078697Z"Sarin, Nikhil"https://www.zbmath.org/authors/?q=ai:sarin.nikhil"Lasky, Paul D."https://www.zbmath.org/authors/?q=ai:lasky.paul-dSummary: Two neutron stars merge somewhere in the Universe approximately every 10 to 100 s, creating violent explosions potentially observable in gravitational waves and across the electromagnetic spectrum. The transformative coincident gravitational-wave and electromagnetic observations of the binary neutron star merger GW170817 gave invaluable insights into these cataclysmic collisions, probing bulk nuclear matter at supranuclear
densities, the jet structure of gamma-ray bursts, the speed of gravity, and the cosmological evolution of the local Universe, among other things. Despite the wealth of information, it is still unclear when the remnant of GW170817 collapsed to form a black hole. Evidence from other short gamma-ray bursts indicates a large fraction of mergers may form long-lived neutron stars. We review what is known observationally and theoretically about binary neutron star post-merger remnants. From a theoretical perspective, we review our understanding of the evolution of short- and long-lived merger remnants, including fluid, magnetic-field, and temperature evolution. These considerations impact prospects of detection of gravitational waves from either short- or long-lived neutron star remnants which potentially allows for new probes into the hot nuclear equation of state in conditions inaccessible in terrestrial experiments. We also review prospects for determining post-merger physics from current and future electromagnetic observations, including kilonovae and late-time X-ray and radio afterglow observations.AdS graviton stars and differential configurational entropyhttps://www.zbmath.org/1483.850022022-05-16T20:40:13.078697Z"da Rocha, Roldao"https://www.zbmath.org/authors/?q=ai:da-rocha.roldao-jun|rocha.roldao-daSummary: AdS graviton stars are studied in the differential configurational entropy setup, as solutions of the effective Einstein field equations that backreact to compactification. With the critical central density of AdS graviton stars, the differential configurational entropy is derived and computed, presenting global minima for a wide range of stellar mass magnitude orders. It indicates insular domains of configurational stability for AdS graviton stars near astrophysical neutron star densities. Other relevant features are also reported.Galactic clustering under power-law modified Newtonian potentialhttps://www.zbmath.org/1483.850062022-05-16T20:40:13.078697Z"Khanday, Abdul W."https://www.zbmath.org/authors/?q=ai:khanday.abdul-w"Upadhyay, Sudhaker"https://www.zbmath.org/authors/?q=ai:upadhyay.sudhaker"Ganai, Prince A."https://www.zbmath.org/authors/?q=ai:ganai.prince-ahmadSummary: We estimate galaxy clustering under a modified gravitational potential. In particular, the modifications in gravitational potential energy occur due to a power-law and cosmological constant terms. We derive a canonical partition function for the system of galaxies interacting under such a modified gravitational potential. Moreover, we compute various thermodynamical equation of states for the system. We do comparative analysis in order to emphasize the effect of corrections on thermodynamics of the system. Interestingly, the modifications in thermodynamical quantities are embedded in clustering parameter only.Hawking-like radiation of charged particles via tunneling across the lightcylinder of a rotating magnetospherehttps://www.zbmath.org/1483.850072022-05-16T20:40:13.078697Z"Li, Huiquan"https://www.zbmath.org/authors/?q=ai:li.huiquanSummary: In rotating magnetospheres planted on compact objects, there usually exist lightcylinders (LC), beyond which the rotation speed of the magnetic field lines exceeds the speed of light. The LC is a close analog to the horizon in gravity, and is a casual boundary for charged particles that are restricted to move along the magnetic field lines. In this work, it is proposed that there should be Hawking-like radiation of charged particles from the LC of a rotating magnetosphere from the point of view of tunneling by using the field sheet metric.Aspects of GRMHD in high-energy astrophysics: geometrically thick disks and tori agglomerates around spinning black holeshttps://www.zbmath.org/1483.850102022-05-16T20:40:13.078697Z"Pugliese, D."https://www.zbmath.org/authors/?q=ai:pugliese.daniela"Montani, G."https://www.zbmath.org/authors/?q=ai:montani.giovanniSummary: This work focuses on some key aspects of the general relativistic (GR) -- magneto-hydrodynamic (MHD) applications in high-energy astrophysics. We discuss the relevance of the GRHD counterparts formulation exploring the geometrically thick disk models and constraints of the GRMHD shaping the physics of accreting configurations. Models of clusters of tori orbiting a central super-massive black hole (\textbf{SMBH}) are described. These orbiting tori aggregates form sets of geometrically thick, pressure supported, perfect fluid tori, associated to complex instability processes including tori collision emergence and
empowering a wide range of activities related expectantly to the embedding matter environment of Active Galaxy Nuclei. Some notes are included on aggregates combined with proto-jets, represented by open cusped solutions associated to the geometrically thick tori.
This exploration of some key concepts of the GRMHD formulation in its applications to High-Energy Astrophysics starts with the discussion of the initial data problem for a most general Einstein-Euler-Maxwell system addressing the problem with a relativistic geometric background. The system is then set in quasi linear hyperbolic form, and the reduction procedure is argumented. Then, considerations follow on the analysis of the stability problem
for self-gravitating systems with determined symmetries considering the perturbations also of the geometry part on the quasi linear hyperbolic onset. Thus we focus on the ideal GRMHD and self-gravitating plasma ball. We conclude with the models of geometrically thick GRHD disks gravitating around a Kerr \textbf{SMBH} in their GRHD formulation and including in the force balance equation of the disks the influence of a toroidal magnetic field, determining its impact in tori topology and stability.The shadows and observational appearance of a noncommutative black hole surrounded by various profiles of accretionshttps://www.zbmath.org/1483.850112022-05-16T20:40:13.078697Z"Zeng, Xiao-Xiong"https://www.zbmath.org/authors/?q=ai:zeng.xiaoxiong"Li, Guo-Ping"https://www.zbmath.org/authors/?q=ai:li.guoping"He, Ke-Jian"https://www.zbmath.org/authors/?q=ai:he.ke-jianSummary: The accretion around the black hole plays a pivotal role in the theoretical analysis of black hole shadow, and of the black hole observation in particular. We mainly study the shadow and observation characteristics of noncommutative Schwarzschild black holes wrapped by three accretion models, and then explore the influence of noncommutative parameters on the observation appearance and spacetime geometry of black holes. When the black hole is surrounded by an optically and geometrically thin accretion disk, it shows that the direct emissions always dominate the total observed intensity, while the lensing ring superimposed upon the direct emission produces a thin ring, which improves the observation intensity of the black hole image. However, the photon rings makes negligible contributions to the total observed brightness due to its exponential narrowness, although the photon ring intersects the thin plane more than three times to pick up larger intensity.
More importantly, when the noncommutative parameters changed, the corresponding regions and observation intensities of photon ring, lensing ring and direct emission all change correspondingly. For optical thin spherically symmetric accretion, we consider the static and infalling matters, respectively. We find that the observation intensity of the two spherical accretion models increase with the increase of noncommutative parameters. In addition, due to the Doppler effect of the infalling movement, the shadow image of infalling accretion is darker than that of static accretion. In a word, the different accretion models and noncommutative parameters will lead to different shadow images and optical appearances of noncommutative Schwarzschild black holes.The effect of stationary axisymmetric spacetimes in interferometric visibilityhttps://www.zbmath.org/1483.850122022-05-16T20:40:13.078697Z"Basso, Marcos L. W."https://www.zbmath.org/authors/?q=ai:basso.marcos-l-w"Maziero, Jonas"https://www.zbmath.org/authors/?q=ai:maziero.jonasSummary: In this article, we consider a scenario in which a spin-1/2 quanton goes through a superposition of co-rotating and counter-rotating circular paths, which play the role of the paths of a Mach-Zehnder interferometer in a stationary and axisymmetric spacetime. Since the spin of the particle plays the role of a quantum clock, as the quanton moves in a superposed path it gets entangled with the momentum (or the path), and this will cause the interferometric visibility (or the internal quantum coherence) to drop, since, in stationary axisymmetric spacetimes there is a difference in proper time elapsed along the two trajectories. However, as we show here, the proper time of each path will couple to the corresponding local Wigner rotation, and the effect in the spin of the superposed particle will be a combination of both. Besides, we discuss a general framework to study the local Wigner rotations of spin-1/2 particles in general stationary axisymmetric spacetimes for circular orbits.Anisotropic star models in the context of vanishing complexityhttps://www.zbmath.org/1483.860092022-05-16T20:40:13.078697Z"Arias, C."https://www.zbmath.org/authors/?q=ai:arias.clemente-f|arias.cesar|arias.carlos-andres|arias.carlos-f"Contreras, E."https://www.zbmath.org/authors/?q=ai:contreras.ernesto"Fuenmayor, E."https://www.zbmath.org/authors/?q=ai:fuenmayor.e"Ramos, A."https://www.zbmath.org/authors/?q=ai:ramos.arthur-f|ramos.angel-manuel|ramos.alex-d|ramos.alexis|ramos.angels|ramos.alvaro-kruger|ramos.anderson-j-a|ramos.amber|ramos.ana-rita|ramos.airton|ramos.antonio-g|ramos.alexandre-ferreira|ramos.alice-a|ramos.anabela|ramos.a-diaz|ramos.alberto-gil-c-p|ramos.alberto|ramos.adriana|ramos.alexandra|ramos.alfonso|ramos.a-l-l|ramos.arturo|ramos.ana-primo|ramos.a-b-m|ramos.andres|ramos.a-a-g-f|ramos.alberto.2|ramos.augustoSummary: We use the definition of complexity for static and self- gravitating objects to build up three physical general relativistic anisotropic models fulfilling the vanishing complexity condition which serves to provide the extra information needed to close the system of Einstein field equations. We evaluate the physical acceptability of these models by testing some of the conditions that the geometric and material sector must satisfy in order to be considered as reasonable realistic models. We present the results of this analysis by asserting that the studied cases demonstrate to be feasible and stable under the chosen set of parameters. Furthermore, the \(P_\bot=0\) and the Consenza's anisotropy models that seem not satisfying the expect conditions are also discussed.