JournalTOCs

General Relativity and Gravitation
Journal Prestige (SJR): 0.598

Citation Impact (citeScore): 1
Number of Followers: 2

Hybrid journal (It can contain Open Access articles)
ISSN (Print) 1572-9532 - ISSN (Online) 0001-7701
Published by Springer-Verlag

[2468 journals]

Hamilton–Jacobi framework for Regge–Teitelboim gravity
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  Abstract: Abstract In higher co-dimension, we discuss the Hamilton–Jacobi formalism for brane gravity described by the Regge–Teitelboim model, in higher co-dimension. Considering that it is originally a second-order in derivatives singular theory, we analyze its constraint structure by identifying the complete set of Hamilton–Jacobi equations, under Carathéodory’s equivalent Lagrangians method, which goes hand in hand with the study of the integrability for this type of gravity. Besides, we calculate the characteristic equations, including the one that satisfies the Hamilton principal function S. We find the presence of involutive and non-involutive constraints so that by properly defining a generalized bracket, the non-involutive constraints that originally arise in our framework are removed while the set of parameters related to time evolution and gauge transformations is identified. A detailed comparison is also made with a recent Ostrogradsky–Hamilton approach for constrained systems, developed for this brane gravity. Some facts about the gauge symmetries behind this theory are discussed.
  PubDate: 2023-09-19
The bimetric model with an informational metric tensor
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  Abstract: Abstract We consider a hybrid bimetric model where, in addition to the ordinary metric tensor that determines geometry, an informational metric is introduced to describe the reference frame of an observer. We note that the local information metric being Minkowskian explains one of the key aspects of the Einstein equivalence principle. Our approach has the potential to justify the three-dimensional nature of physical space and address the gravitational energy puzzle. Furthermore, it appears to be free of ghost instabilities in the matter sector, as the second metric tensor couples exclusively to the observer and is non-dynamical.
  PubDate: 2023-09-19
Stationary, charged Zipoy–Voorhees metric from colliding wave
spacetime
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  Abstract: Abstract Through the Ernst formalism we provide expression for a class of colliding Einstein-Maxwell (EM) metrics with cross polarization. Local isometry is imposed as a means to transform interaction region of the spacetime into stationary, charged Zipoy–Voorhees (ZV) metric in Schwarzschild coordinates. This is known as the Chandrasekhar-Xanthopoulos (CX) duality which maps the plane of double-null coordinates (with two spacelike cyclic coordinates) to the static/stationary spacetime. The ZV-metric is known to describe planetary/stellar objects with arbitrary distortion parameter. Asymptotic behaviour of the metric for practical use is provided. "The world may be seen in a grain of sand" - William Blake.
  PubDate: 2023-09-15
Cosmological distances and hubble tension in Einstein–Cartan theory
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  Abstract: Abstract We analyze the measurement of cosmological distances in the presence of torsion in both Einstein–Cartan and Poincaré gauge theory of gravity. Using the modified cosmological distance measurements, we use the observed time delays in gravitational lensing systems to determine the Hubble parameter. The results show the measured Hubble parameter from a lensing system can be less than its expected value in General Relativity for certain models of torsion and its associated density parameter. This can reduce the tension between late-time and early-universe measurements of the Hubble parameter, the so-called Hubble tension.
  PubDate: 2023-09-14
Large scale structure formation for conformal theory of gravity
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  Abstract: Abstract We assume a modified (conformal) gravity theory, which produces a stronger interaction at large scale, in order to discuss the statistical distribution of the galaxy clusters based on thermodynamics. We develop N-body partition function and exploit it to study the equations of state of the system. The probability distribution function is deduced from the partition function taking the modified gravity theory into account. We compare the theoretical model with the data available through SDSS (III) via its 12th data release.
  PubDate: 2023-09-13
The covariant approach to static spacetimes in Einstein and extended
gravity theories
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  Abstract: Abstract We present a covariant study of static space-times, as such and as solutions of gravity theories. By expressing the relevant tensors through the velocity and the acceleration vectors that characterise static space-times, the field equations provide a natural non-redundant set of scalar equations. The same vectors suggest the form of a Faraday tensor, that is studied in itself and in (non)-linear electrodynamics. In spherical symmetry, we evaluate the explicit expressions of the Ricci, the Weyl, the Cotton and the Bach tensors. Simple restrictions on the coefficients yield well known and new solutions in Einstein, f(R), Cotton and Conformal gravity, with or without charges, in vacuo or with fluid source.
  PubDate: 2023-09-13
Critical compactness bound of a class of compact stars
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  Abstract: Abstract Tolman VII solution (Tolman in Phys Rev 55(4):364, 1939) is an exact analytic solution to the Einstein field equations describing the space-time of a static spherically symmetric distribution of matter. The solution has been shown to be capable of describing the interior of compact objects like neutron stars. Generalized (Raghoonundun and Hobill in Phys Rev D 92(12):124005, 2015) and modified (Jiang and Yagi in Phys Rev D 99(12):124029, 2019) versions of the solution are also available in the literature, which have been subsequently developed to accommodate a wide range of neutron star EOS. The stability of the modified Tolman VII solution has recently been analyzed (Posada et al in Phys Rev D 103(10):104067, 2021), which provides a critical value of the adiabatic index above which the stellar configuration becomes unstable against radial oscillations. In this paper, making use of the generalized version of the Tolman VII solution, we prescribe an upper bound on the compactness (M/R) beyond which the star becomes unstable against radial oscillations (Chandrasekhar in Phys Rev Lett 12(4):114, 1964). Our study brings to attention the role of model parameters in the generalized Tolman VII solution. The analysis also provides new insight into the role of inhomogeneity of the matter distribution vis-a-vis equation of state (EOS) on the compactness of a relativistic star.
  PubDate: 2023-09-05
Probing naked singularities in the charged and uncharged $$\gamma -
metrics$$ with quantum wave packets
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  Abstract: Abstract The non-trivial naked singularities that possess directional behavior in the charged and uncharged Zipoy-Voorhees (ZV) spacetimes, known as $ \gamma - metrics $ are investigated within the context of quantum mechanics. Classically singular spacetime is understood as a geodesic incompleteness with respect to a particle probe, while quantum singularity is understood as a non-unique evolution of test quantum wave packets. In this study, quantum wave packets obeying Klein–Gordon equation are used to probe timelike naked singularities. It is shown by rigorous mathematical calculations that the outermost singularity developed in the charged and uncharged ZV spacetime on the equatorial plane is quantum mechanically singular for all values of the deformation parameter $\gamma $ . However, directional singularities that develop on the symmetry axis is shown to be healed partially for specific range of the parameter $\gamma $ , if the analysis is restricted purposely to only specific mode (s-wave mode). Allowing arbitrary modes, classical directional singularities remains quantum singular.
  PubDate: 2023-09-01
Black hole evolution in the Bondi–Hoyle–Lyttleton accretion
model
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  Abstract: Abstract In this paper, we exhibit analytical solutions for the evolution of the mass of an astrophysical object accreting cosmic fluid according to the Bondi–Hoyle–Lyttleton mechanism. The key assumption of this model is that the adiabatic speed of sound within the accreted fluid directly affects the rate of change of the mass of the accreting object. We consider different literature equations of state, as the (Modified) Berthelot, Logotropic, generalized polytropic of index n, and quadratic models. We assume the fluid to evolve either according to General Relativity or to the Randall-Sundrum type 1 gravity model far away from the astrophysical object in an asymptotically Friedman universe. We claim that this accretion mechanism is unlikely to affect the mass-radius relationship of the photon sphere beyond the Schwarzschild one at the present time, and that the critical point of accretion in the (Modified) Berthelot fluid flow is hidden by the event horizon. Our work belongs to the broader research line investigating the interplay of small-scale and large-scale Physics in the modeling of gravitational phenomena.
  PubDate: 2023-08-26
The thermodynamical properties of dS black holes in Einstein gravity with
torsion induced by the spinor
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  Abstract: Abstract We investigate the thermodynamical properties of de Sitter black holes in (2+1) dimensional Einstein gravity with torsion, induced by spinors. Using the methods of Kraus, Keski-Vakkuri, and Wilczek, we calculate the entropy, temperature, and Hawking radiation from the dS black hole with torsion that has the event and cosmological horizons due to the presence of a positive cosmological constant. We show that the temperatures associated with the event and the cosmological horizons are not equal. We also obtain that the entropies associated with these horizons to differ from the standard Bekenstein-Hawking result.
  PubDate: 2023-08-24
Observational constraints on teleparallel effective equation of state
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  Abstract: Abstract A cluster of astronomical observations emerged that the present Universe is in a phase of accelerated expansion. To examine the accelerated expansion of the Universe, we used the newly proposed gravity in which torsion scalar is responcible for the accelerated expansion. The investigation is carried out using a parameterized effective equation of state with the free parameters $\alpha $ , $\beta $ , $\omega _{0}$ and $\omega _{1}$ . Also, for the analysis we consider the model of the form $f(T)=m (-T)^{n}$ , where $m \ne 0$ and n are the constants. By constraining the model with the combined H(z), SC, unCorBAO sample datasets. The model appeared to be in good agreement with the observations, and we were able to determine the parameter values that fit the data the best. Finally, we examined how the deceleration parameter and equation of state parameter behaved in relation to the parameter values that best suited the data.
  PubDate: 2023-08-23
Kiselev black holes in f(R, T) gravity
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  Abstract: Abstract We obtain new exact solutions for the gravitational field equations in the context of f(R, T) gravity, thereby obtaining different classes of black holes surrounded by fluids, taking into account some specific values of the parameter of the equations of state, w. In order to obtain these solutions in the context of f(R, T) gravity, we consider viable particular choices of the f(R, T). Considering an anisotropic energy-momentum tensor, we write the field equations with the required symmetries for this type of solution. Then, we analyze the conditions of energy in a general way and also for particular values of the parameter w of the equation of state. In addition, thermodynamic quantities, such as Hawking temperature and mass associated to the horizons of solutions, are taken into account in our analysis.
  PubDate: 2023-08-22
Toward fixing a framework for conformal cyclic cosmology
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  Abstract: Abstract Conformal Cyclic Cosmology (CCC) is a cyclic model of the universe put forward by Sir Roger Penrose (Cycles of Time: An Extraordinary New View of the Universe, Random House, Manhattan, 2010). A conformal invariance assumption in the neighbourhood of the crossover region between cycles (which Penrose calls aeons) allows successive space-times to be related by a conformal rescaling. A major open problem is how to choose the conformal factor in a unique way, and is a fundamental hurdle to further study. Proposals have been put forward by Newman (Gen Relativ Gravit 46(5):1–13, 2014), Tod (Gen Relativ Gravit 47(3):1–13, 2015) and Nurowski (Class Quantum Gravity 38(14):145004, 2021), but they disagree in one way or another with Penrose’s original assumptions as well as each other. In this paper we compare these different models in detail and rule out certain choices for the conformal factor that have been put forward by Penrose. We extend the results of Newman and fix inconsistencies that arose in his calculations. A new class of solutions are put forward which agree with Penrose’s assumptions exactly so long as a certain additional relation is satisfied.
  PubDate: 2023-08-19
Algebraic properties of Riemannian manifolds
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  Abstract: Abstract Algebraic properties are explored for the curvature tensors of Riemannian manifolds, using the irreducible decomposition of curvature tensors. Our method provides a powerful tool to analyze the irreducible basis as well as an algorithm to determine the linear dependence of arbitrary Riemann polynomials. We completely specify 13 independent basis elements for the quartic scalars and explicitly find 13 linear relations among 26 scalar invariants. Our method provides several completely new results, including some clues to identify 23 independent basis elements from 90 quintic scalars, that are difficult to find otherwise.
  PubDate: 2023-08-17
Dissipative properties of relativistic fluids in a general curved
space–time
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  Abstract: Abstract Dissipative force–flux relations are established in a strict covariant fashion for a relativistic fluid in a general curved space–time within the framework of kinetic theory. The Boltzmann equation is addressed to first order in the gradients by employing the Chapman–Enskog expansion and the corresponding constitutive equations are derived by considering a relaxation approximation. It is shown that in the heat flux, only the corresponding transport coefficient is modified when the gradients of the state variables are considered as the thermodynamic forces. On the other hand, the viscous terms features new driving terms due to the curvature of space–time that only vanish in particular cases.
  PubDate: 2023-08-11
GUP corrected Casimir wormholes in f(Q) gravity
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  Abstract: Abstract We have systematically presented the effect of the generalized uncertainty principle (GUP) in Casimir wormhole space-time in the recently proposed modified gravity, the so-called symmetric teleparallel gravity, or f(Q) gravity. We consider two famous GUP models, such as the Kempf, Mangano, and Mann (KMM) model and the Detournay, Gabriel, and Spindel (DGS) model, in this study. Also, to find the solutions, we assumed two different f(Q) forms and obtained analytic as well as numerical solutions under the effect of GUP. Besides this, we investigate the solutions with three different redshift functions under an anisotropic fluid located at the throat. Further, we analyzed the obtained wormhole solutions with energy conditions, especially null energy conditions at the wormhole’s throat, and encountered that some arbitrary quantity disrespects the classical energy conditions at the wormhole throat of radius $r_0$ . Later, the ADM mass and the volume integral quantifier are also discussed to calculate the amount of exotic matter required near the wormhole throat. Additionally, we show the behavior of the equation of state parameters under the effect of GUP.
  PubDate: 2023-08-10
String-like brane splitting in the context of $$f(T,\mathcal {B})$$
gravity
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  Abstract: Abstract In this work, the influence of the boundary term $\mathcal {B}$ is analyzed in a string-like thick brane scenario in the gravity context $f(T,\mathcal {B})$ . For that, three models of $f(T,\mathcal {B})$ are proposed, i. e., $f_1(T,\mathcal {B})=T+k\mathcal {B}^{n}$ , $f_2(T,\mathcal {B})=T+k(-T+\mathcal { B})^{n}$ and $f_3(T,\mathcal {B})=T+k_1T^2+k_2\mathcal {B}^2$ , where n, k and $k_{1,2}$ are parameters that control the deviation from the usual teleparallelism. The first relevant result obtained was the appearance of a super-located tower in the core for energy density. Furthermore, the greater the influence of the boundary term, the new maximums and minimums appear in the energy density. All this indicates the emergence of capable structures from split to the brane. The second relevant result was obtained by analyzing the gravitational perturbations, where the effective potential presents the supersymmetric form of quantum mechanics, leading to well-localized massless modes.
  PubDate: 2023-07-31
Cosmological solutions through gravitational decoupling in $$f({\mathcal
{R}},{\mathcal {T}},{\mathcal {R}}_{\textrm{ab}}{\mathcal
{T}}^{\textrm{ab}})$$ gravity
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  Abstract: Abstract In this paper, we adopt minimal gravitational decoupling scheme to extend a non-static spherically symmetric isotropic composition to anisotropic interior in $f({\mathcal {R}},{\mathcal {T}},{\mathcal {R}}_{\textrm{ab}}{\mathcal {T}}^{\textrm{ab}})$ theory. A geometric deformation is applied only on $g_{rr}$ metric component through which the modified field equations are separated into two sets, each of them correspond to their parent (seed and newly added) source. An isotropic model suggested by the Friedmann–Lemaitre–Robertson–Walker metric is adopted to reduce the unknowns in the first set. We then obtain an isotropic solution by making use of a linear equation of state and a particular form of the scale factor. A density-like constraint is chosen to solve the other sector containing the deformation function and multiple components of an additional matter source. Further, the graphical interpretation of the developed model is carried out to analyze how a decoupling parameter and modified gravity influence the evolutionary phases of the universe. It is concluded that only the radiation-dominated era meets stability criteria everywhere in this matter-geometry coupled theory.
  PubDate: 2023-07-27
Solutions of a charged scalar field in five-dimensional helicoid solution
with electromagnetic field
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  Abstract: Abstract We study a charged and massive scalar field in the background of the Nutku-Ghezelbash-Kumar metric which is obtained by the addition of a time coordinate to the Nutku helicoid metric in a non-trivial way. The angular part of the Klein-Gordon equation can be written as a double confluent Heun equation. The radial equation cannot be solved in terms of a known function in its general form. However, in some special cases, the radial equation can also be written explicitly as a double confluent Heun equation. We study the full radial equation numerically and observe that the electromagnetic field parameter defines an effective cut-off on the range of the radial coordinate. Finally, we obtain a quasi-exact solution with an approximation.
  PubDate: 2023-07-27
Einstein’s equations and the pseudo-entropy of pseudo-Riemannian
information manifolds
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  Abstract: Abstract Motivated by the corrected form of the entropy-area law, and with the help of von Neumann entropy of quantum matter, we construct an emergent spacetime by the virtue of the geometric language of statistical information manifolds. We discuss the link between Wald and Jacobson approaches of thermodynamic/gravity correspondence and Fisher pseudo-Riemannian metric of information manifold. We derive in detail Einstein’s field equations in statistical information geometric forms. This results in finding a quantum origin of a positive cosmological constant that is founded on Fisher metric. This cosmological constant resembles those found in Lovelock’s theories in a de Sitter background as a result of using the complex extension of spacetime and the Gaussian exponential families of probability distributions, and we find a time varying dynamical gravitational constant as a function of Fisher metric together with the corresponding Ryu–Takayanagi formula of such system. Consequently, we obtain a dynamical equation for the entropy in information manifold using Liouville–von Neumann equation from the Hamiltonian of the system. This Hamiltonian is suggested to be non-Hermitian, which corroborates the approaches that relate non-unitary conformal field theories to information manifolds. This provides some insights on resolving “the problem of time”.
  PubDate: 2023-07-21