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Similar Journals
 General Relativity and GravitationJournal Prestige (SJR): 0.598 Citation Impact (citeScore): 1Number of Followers: 0      Hybrid journal (It can contain Open Access articles) ISSN (Print) 1572-9532 - ISSN (Online) 0001-7701 Published by Springer-Verlag  [2469 journals]
• Notes on complexity growth rate, grand potential and partition function

Abstract: Abstract We examine the complexity/volume conjecture and further investigate the possible connections between complexity and partition function. The complexity/partition function relation is then utilized to study the complexity of the thermofield double state of extended SYK models for various conditions.The difference between the complexity/partition function relation with the complexity/action duality comes from the fact that partition function can be evaluated from more than one saddle point, so they differ at most at the non-perturbative level. We further analyze free energy and the growth rate of complexity in the neutral AdS-Vaidya black hole formed by collapsing an uncharged spherically symmetric thin shell of null fluid. The relation between the late-time complexity growth rate and black hole/SYK wormhole phase transition is also discussed. Finally, we check the Lloyd bound with our proposal.
PubDate: 2022-05-22

• Space-like singularities of general relativity: A phantom menace'

Abstract: Abstract The big bang and the Schwarzschild singularities are space-like. They are generally regarded as the ‘final frontiers’ at which space–time ends and general relativity breaks down. We review the status of such space-like singularities from three increasingly more general perspectives. They are provided by (i) A reformulation of classical general relativity motivated by the Belinskii, Khalatnikov, Lifshitz conjecture on the behavior of the gravitational field near space-like singularities; (ii) The use of test quantum fields to probe the nature of these singularities; and, (iii) An analysis of the fate of these singularities in loop quantum gravity due to quantum geometry effects. At all three levels singularities turn out to be less menacing than one might a priori expect from classical general relativity. Our goal is to present an overview of the emerging conceptual picture and suggest lines for further work. In line with the Introduction to Current Research theme, we have made an attempt to make it easily accessible to all researchers in gravitational physics.
PubDate: 2022-05-21

• AdS black holes with perfect fluid dark matter and weak cosmic censorship
conjecture

Abstract: Abstract By considering the absorption of a charged particle, the thermodynamic laws and weak cosmic censorship conjecture are investigated for Reissner–Nordstöm–anti–de Sitter black holes with prefect fluid dark matter. We find that the first law of thermodynamics and the second law of thermodynamics are still valid in AdS spacetime with dark matter. In particular, we test the validity of weak cosmic censorship conjecture by studying how the minimum value of the function that determines the position of the horizon changes. As a result, it shows that there are always horizons that make the weak cosmic censorship conjecture hold, and the extreme black holes can evolve into non-extreme black holes in dark matter background.
PubDate: 2022-05-05

• Modified theories of gravity: Why, how and what'

Abstract: Abstract General relativity (GR) was proven via the direct detection of gravitational waves from the mergers of the binary black holes and binary neutron stars by the advanced LIGO and advanced virgo detectors. These detections confirmed the prediction of GR and provided the first direct evidence of the existence of stellar-mass black holes (BHs). However, the occurrence of singularities at the centers of BHs suggests that GR is inapplicable because of the breakdown of the equivalence principle at the singularities. The fact that these singularities exist indicates that GR cannot be a universal theory of space–time. In the low-energy limit, the theoretical and observational challenges faced by the $$\Lambda$$ CDM model also indicate that we might have to look beyond GR as the underlying theory of gravity. Unlike GR, whose field equations contain only up to second-order derivatives, the modified theories with higher derivative Ricci/Riemann tensor gravity models include higher derivatives. Therefore, one expects significant differences between GR and modified theories. Since there are many ways of modifying GR in the strong-gravity and cosmological distances, each model has unique features. This leads to the following crucial question: Are there a set of unique signatures that distinguish GR from modified gravity (MG) theories' This review discusses three aspects of MG theories: (1) Why do we need to consider MG theories' (2) How to modify GR' and (3) What are the observational consequences' The review is written in a pedagogical style with the expectation that it will serve as a useful reference for theorists and observers and those interested in bridging the divide between theory and observations.
PubDate: 2022-05-05

• Investigating the environmental dependence of ultralight scalar dark
matter with atom interferometers

Abstract: Abstract We study the environmental dependence of ultralight scalar dark matter (DM) with linear interactions to the standard model particles. The solution to the DM field turns out to be a sum of the cosmic harmonic oscillation term and the local exponential fluctuation term. The amplitude of the first term depends on the local DM density and the mass of the DM field. The second term is induced by the local distribution of matter, such as the Earth. And it depends not only on the mass of the Earth, but also the density of the Earth. Then, we compute the phase shift induced by the DM field in atom interferometers (AIs), through solving the trajectories of atoms. Especially, the AI signal for the violation of weak equivalence principle (WEP) caused by the DM field is calculated. Depending on the values of the DM coupling parameters, contributions to the WEP violation from the first and second terms of the DM field can be either comparable or one larger than the other. Finally, we give some constraints to DM coupling parameters using results from the terrestrial atomic WEP tests.
PubDate: 2022-04-29

• Loop quantum gravity with optimal control path integral, and application
to black hole tunneling

Abstract: Abstract This paper presents a novel path integral formalism for Einstein’s theory of gravitation from the viewpoint of optimal control theory. Despite its close connection to the well-known variational principle of physicists, optimal control turns out to be more general. Within this context, a Lagrangian which is different from the Einstein-Hilbert Lagrangian is defined. Einstein’s field equations are recovered exactly with variations of the new action functional. The quantum theory is obtained using Ashtekar variables and the loop scalar product. As an illustrative example, the tunneling process of a black hole into another black hole or into a white hole is investigated with a toy model.
PubDate: 2022-04-29

• Editorial note to: On the transition from wave optics to geometric optics
in general relativity by Jürgen Ehlers

PubDate: 2022-04-20

• Republication of: On the transition from wave optics to geometric optics
in general relativity

Abstract: Abstract This paper considers the relationship between electromagnetic waves and the geometric optics approximation in general relativity. The approximation is widely used in predictions of observations in astronomy and cosmology, for example in gravitational lensing and the cosmic microwave background. Its properties are thus of considerable significance. The paper’s author was a Golden Oldies board member and a prominent author and editor for Springer. It complements other Golden Oldies by Ehlers showing the importance and influence of his attention to issues concerning the relation of exact physical theories and their approximations.
PubDate: 2022-04-20

• Thermodynamics of multi-horizon spacetimes

Abstract: Abstract There exist several well-established procedures for computing thermodynamics for a single horizon spacetime. However, for a spacetime with multi-horizon, the thermodynamics is not very clear. It is not fully understood whether there exists a global temperature for the multi-horizon spacetime or not. Here we show that a global temperature can exist for Schwarzschild-de Sitter spacetime, Reissner-Nordstrom-de Sitter spacetime, and rotating BTZ black hole. This temperature does not coincide with the conventional Hawking temperature related to the outer horizon. We also show that the total entropy for these spacetimes can not be determined only by the outer horizon. The correlations between the horizons of these spacetimes determine it.
PubDate: 2022-04-19

• A comprehensive study of modulation effects on CMB polarization

Abstract: Abstract The Cosmic Microwave Background is characterized by temperature and linear polarization fields. Dipole modulation in the temperature field has been extensively studied in the context of hemispherical power asymmetry. In this article, we show that a dipole modulation, and in general, any kind of modulation isn’t allowed in the E and B modes. This is the main result of this paper. This result explains why no evidence of modulation in E mode has been found in the literature. On the contrary, the linear polarization fields Q and U have no such restrictions. We show that modulation under certain situations can be thought of as local U(1) gauge transformations on the surface of a sphere. As far as the modulation function is concerned, we show that physical considerations enforce it to be (i) a spin 0 field and (ii) a scalar under parity. As masking is a specific type of modulation, our study suggests that a direct masking of E mode isn’t also possible. Masking in E map can only be applied through Q and U fields. This means that in principle, leaking of E and B mode powers into each other is unavoidable.
PubDate: 2022-04-17

• Republication of: Existence theorem for the Einsteinian gravitational
field equations in the non-analytic case

Abstract: Abstract This paper was the first announcement of results later elaborated in detail in the more extensive 1952 paper by the same author (now Prof. Yvonne Choquet-Bruhat). They provide a very important theorem on the uniqueness of solutions of the initial value problem for the Einstein equations. This showed that Einstein’s theory shared the property of other physical theories that the evolution of the system is unique given the initial “position” and “velocity”, which here are the Cauchy data for the metric and its derivative.
PubDate: 2022-04-12

• Editorial note to: Existence theorem for the Einsteinian gravitational
field equations in the non-analytic case, by Yvonne Fourès-Bruhat

PubDate: 2022-04-12

• Solutions for the null-surface formulation in $$2+1$$ 2 + 1 dimensions
leading to spacetimes of Petrov types I, II, and D

Abstract: Abstract The only nontrivial exact solutions reported to-date for the field equations of the null-surface formulation (NSF) of general relativity are for the ( $$2+1$$ )-dimensional version of the theory, where three such solutions are known. This work presents a new family of NSF solutions. The corresponding general relativistic spacetimes are shown to span three different Petrov types, depending upon the choices that are made for various parameters. All of the scalar invariants for the spacetimes are constant, as are all of the eigenvalues of the Cotton-York tensor. The physical nature of a possible source term is discussed in detail, and two of the previously known NSF solutions are presented as special cases. The new family of solutions was derived by assuming additive separability—meaning that the dependent variable in the field equations is represented as a sum. This effectively turns the main NSF field equation (which is a partial differential equation) into an ordinary differential equation that is exactly solvable. The possibility of adapting this approach to the ( $$3+1$$ )-dimensional version of the NSF is discussed.
PubDate: 2022-04-10

• A family of horizon-penetrating coordinate systems for the Schwarzschild
black hole geometry with Cauchy temporal functions

Abstract: Abstract We introduce a new family of horizon-penetrating coordinate systems for the Schwarzschild black hole geometry that feature time coordinates, which are specific Cauchy temporal functions, i.e., the level sets of these time coordinates are smooth, asymptotically flat, spacelike Cauchy hypersurfaces. Coordinate systems of this kind are well suited for the study of the temporal evolution of matter and radiation fields in the joined exterior and interior regions of the Schwarzschild black hole geometry, whereas the associated foliations can be employed as initial data sets for the globally hyperbolic development under the Einstein flow. For their construction, we formulate an explicit method that utilizes the geometry of—and structures inherent in—the Penrose diagram of the Schwarzschild black hole geometry, thus relying on the corresponding metrical product structure. As an example, we consider an integrated algebraic sigmoid function as the basis for the determination of such a coordinate system. Finally, we generalize our results to the Reissner–Nordström black hole geometry up to the Cauchy horizon. The geometric construction procedure presented here can be adapted to yield similar coordinate systems for various other spacetimes with the same metrical product structure.
PubDate: 2022-04-10

• Influence of the Schwinger effect on radiatively corrected Higss
inflationary magnetogenesis

Abstract: Abstract 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 magnetic fields. We consider radiatively corrected Higgs inflation potential of our previous work in (Kamarpour, M.: Magnetogenesis in Higgs inflation model. General Relat. Gravit. (2021). https://doi.org/10.1007/s10714-021-02824-0). In comparison to the Starobinsky potential, we obtain an extra term as a one loop correction and determine the spectrum of generalized electromagnetic fields. For two values of coupling parameter $$\chi _{1}=5\times 10^{9}$$ and $$\chi _{1}=7.5\times 10^{9}$$ , the back-reaction is weak and our analysis is valid. When we switch on the Schwinger effect,there is no difference in background inflaton field. Therefore, for range of parameters considered and analyzed in this model, the Schwinger effect in Radiatively corrected Higgs model is quite negligible and play no roles in magnetogenesis.
PubDate: 2022-04-08

• Quasi-local instantaneous charges asymptotics at spatial infinity

Abstract: Abstract The article aims to analyze a construction of charges (conserved quantities) for the gravity field in the (3 $$+$$ 1) decomposition. The construction is based on (3 $$+$$ 1) splitting of conformal Yano–Killing two-form. The splitting leads to charges, defined on Cauchy surface, which are combined from components of Weyl tensor and conformal Killing vector. The relations between the conserved quantities and its classical ADM counterparts are revisited. Asymptotic behavior of the conserved quantities is described. The charges are analyzed for a particular choice of initial data, among others, Bowen–York spinning black hole.
PubDate: 2022-03-30

• Power spectrum for perturbations in an inflationary model for a closed
universe

Abstract: Abstract We derive the power spectrum of primordial quantum fluctuations in an inflationary universe for curvature parameter $${\mathcal {K}}=1$$ . This is achieved through a Born–Oppenheimer type of approximation scheme from the Wheeler–DeWitt equation of canonical quantum gravity using gauge-invariant variables. Compared to the flat model, the closed model exhibits a deficit of power at large scales.
PubDate: 2022-03-28

• Rastall-Maxwell approach for anisotropic charged strange stars

Abstract: Abstract In this work we investigate the Rastall-Maxwell theory around the strange quark matter (SQM). Some solutions are obtained by solving the Modified Tolman-Oppenheimer-Volkoff (TOV) equation in the framework of Rastall gravity. Analysis are performed about the energy condition, the mass-radius relation, the modified TOV equation, the redshift and the stability of the system is checked by exploring the adiabatic index, the compactification factor and the causality condition in order to verify the physical consistency of our model. It comes from our results that for physical values of Rastall parameter, the stellar system is more massive compared to its size. Hence, it emerges from our work that the alternative Rastall theory is a suitable candidate to explain the behavior of massive stellar objects.
PubDate: 2022-03-19

• Dynamics of Hu–Sawicki model in Born–Infeld f(R) gravity
theory

Abstract: Abstract A systematic study on the Born–Infeld theory within the Palatini approach of f(R) gravity has been performed and the field equations are investigated considering the Hu–Sawicki model. We study the dynamics of the system in the background of isotropic Friedmann–Leimaître–Robertson–Walker (FLRW) model as well as anisotropic Bianchi I and V models. A very useful approach known as dynamical system approach (DSA) has been adopted to find the equilibrium points and to study the physical behaviour of the model under consideration. Moreover, the capability of the model to reproduce the sequence of radiation dominated, matter dominated and late time accelerated expansion is investigated. This analysis provides information about the evolution of anisotropy parameter (shear) and spatial curvature with time and their behaviour in the different eras of the cosmic evolution.
PubDate: 2022-03-19

• Wave operators, torsion, and Weitzenböck identities

Abstract: Abstract The current article offers a mathematical toolkit for the study of waves propagating on spacetimes with nonvanishing torsion. The toolkit comprises generalized versions of the Lichnerowicz–de Rham and the Beltrami wave operators, and the Weitzenböck identity relating them on Riemann–Cartan geometries. The construction applies to any field belonging to a matrix representation of a Lie (super) algebra containing an $$\mathfrak {so} \left( \eta _{+}, \eta _{-} \right)$$ subalgebra. These tools allow us to study the propagation of waves on an Einstein–Cartan background at different orders in the eikonal parameter. It stands in strong contrast with more traditional approaches that are restricted to studying only the leading order for waves on this kind of geometry (“plane waves”). The current article focuses only on the mathematical aspects and offers proofs and generalizations for some results already used in physical applications. In particular, the subleading analysis proves that torsion affects the propagation of amplitude and polarization for fields in some representations. These results suggest how one may use gravitational waves and multimessenger events as probes for torsion and the spin tensor of dark matter.
PubDate: 2022-03-17

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