General Relativity and Gravitation最新文献

We explore the thermodynamics of a novel solution for the Reissner-Nordström-Anti-de Sitter (AdS) black hole, uniquely incorporating the Gauss-Bonnet term. Unlike previous studies that primarily focused on standard General Relativity or other modifications, this inclusion allows for a modified entropy formulation, facilitating the computation of key thermodynamic quantities such as Gibbs free energy, the first law of thermodynamics, the equation of state, and Hawking temperature. We identify critical points and graphically represent the relationship between temperature and Gibbs free energy as a function of the horizon radius. Ultimately, we assess the thermal stability of the Reissner-Nordström-AdS black hole within the framework of Gauss-Bonnet gravity, emphasizing the influence of the Gauss-Bonnet term unlike previous studies that primarily focused on standard General Relativity or other modifications. As a result, it is found that the Gauss-Bonnet coupling significantly alters the thermodynamic behavior and stability structure of the black hole, revealing richer phase transition phenomena.

Massive white dwarfs have recently been investigated in extended theories of gravity. In the present work, we construct, for the first time, the equilibrium configurations of white dwarfs in the recently proposed (f(mathcal {R,L,T})) theory of gravity, for the specific case (f(mathcal {R},mathcal {L}, mathcal {T}) = mathcal {R} + alpha mathcal {L} mathcal {T}), where (alpha ) serves as a free parameter within this gravitational theory, (mathcal {R}) is the Ricci scalar, (mathcal {L}) is the matter Lagrangian density and (mathcal {T}) is the trace of the energy-momentum tensor. We numerically solve the Tolman-Oppenheimer-Volkoff-like and mass equations from a set of boundary conditions and the Chandrasekhar equation of state. We show that it is possible to increase the maximum masses of white dwarfs depending on the value of the theory parameter. What constraints this mass increasing is the value of the central density of the white dwarf. Finally, the theory remarkably recovers general relativity and Newtonian limit for small densities.

The Horowitz-Hubeny method has been used to compute the quasinormal frequencies of asymptotically anti-de Sitter backgrounds. For the dimensionally reduced BTZ black hole, in this work we propose a modification of this method and we also use a new procedure to calculate its quasinormal frequencies in a perturbative way. The proposed modification of the Horowitz-Hubeny method works for parameter values of the dimensionally reduced BTZ black hole for which the original version of the method does not converge. The proposed calculation of the quasinormal frequencies in a perturbative series takes as a basis a recently published perturbative method motivated in the improved asymptotic iteration method, and in the dimensionally reduced BTZ black hole, for small values of the inner radius, the perturbative values of the quasinormal frequencies coincide with the numerical values. Furthermore we explore numerically and analytically the quasinormal frequencies of the dimensionally reduced BTZ black hole in the near extremal limit.

Forces parallel to particle trajectories occur in physically meaningful situations, including relativistic cosmology and Einstein frame scalar-tensor gravity. These situations have Newtonian analogues that we discuss to provide intuition about the underlying physics.

We perform the first study of the throttling process and heat engine efficiency of asymptotically Anti-de Sitter charged and rotating black strings in the extended phase space. For the throttling process, we calculate the Joule-Thomson coefficient and inversion temperature. We also depict the inversion and isenthalpic curves in the temperature-pressure plane, thereby identifying the corresponding cooling and heating regions. For the black string heat engine, we obtain analytical expressions for the efficiency of the Carnot and rectangular engine cycles and draw their diagrams in terms of some relevant thermodynamics variables.

In this paper we study the higher dimensional (left( N > 4right) ) homogeneous and isotropic perfect fluid spacetimes in Einstein–Gauss–Bonnet (EGB) gravity. We solve the modified field equations with higher order curvature terms to determine the evolution of the scale factor. We transparently show that this scale factor cannot become smaller than a finite minimum positive value which depends on the dimension and equation of state. This bound completely eliminates any curvature singularities in homogeneous and isotropic spacetimes, where the scale factor must tend to zero. This is a unique property of EGB gravity which, despite being ghost-free and having quasi-linear field equations like general relativity, allows for the violation of singularity theorems. This phenomenon, thus, gives a natural way to dynamically construct regular black holes via higher dimensional continual gravitational collapse.

The null-surface formulation (NSF) of general relativity differs from the usual approach by treating the spacetime metric as a derivable quantity instead of regarding it as fundamental. The NSF has two mathematically equivalent interpretations: (a) Light rays leave a spacetime point and intersect null-infinity to form a ‘light-cone cut,’ which encodes the properties of the spacetime; (b) At null-infinity, angular coordinates (Bondi coordinates) label past light cones. Being null surfaces, these past light cones will satisfy the NSF field equations, the solution of which will provide a description of spacetime. In an earlier work, the present authors gave an exact solution for the NSF field equations in 2+1 dimensions, showing how the solution directly linked the two NSF interpretations. The present paper expands on that work by constructing the corresponding (3+1)-dimensional solution and then, as in 2+1 dimensions, linking the two interpretations so as to illustrate their equivalence. The functions relevant to the 3+1 NSF are calculated, and the field equations are shown to be satisfied. This is the first time that a nontrivial (3+1)-dimensional NSF solution has been found and its properties examined.

We mainly analyze the effective dynamics of scalar particles trapped in a two-dimensional static de Sitter (dS(_{2})) spacetime from the rainbow gravity perspective. For this purpose, in the framework of gravity’s rainbow, we exactly solve the covariant Klein-Gordon equation to reach the wave function identifying relativistic dynamics of scalar particles as well as generate the corresponding energy spectrum, oscillation frequency, particle creation rate, and transmission probability, analyze them thoroughly, and highlight how the results vary depending on the selected rainbow gravity scenario. We found that the investigation implies quite amazing results. One of them is that while the General Theory of Relativity (GTR) does not give physically measurable energy values for the system we are examining, the rainbow approach of gravity allows us to obtain a real energy spectrum. Another conclusion is that if the test particles are confined to a two-dimensional geometry, the particle creation process can be observed even if the space-time model is static. The previous studies in literature indicate that the production of particles occurs in an expanding space-time or depends on the existence of a strong exterior electric field. From this point of view, our study presents a remarkable result for the creation process of relativistic scalar particles.

We study the entanglement entropy in the context of supersymmetric quantum cosmology, focusing on a pair of TAUB-type universes within the microsuperspace sector ((R_{2}rightarrow 0)). Starting from the Lagrangian of a supergravity theory with (mathcal {N}=1) in (D=4), we construct the quantum Hamiltonian and obtain solutions to the Wheeler-DeWitt equation restricted to the subspace defined by first-order fermionic constraints. The resulting solutions take the form of four-component spinor-like wavefunctions, allowing a natural interpretation in terms of internal degrees of freedom. This spinorial structure enables the construction of an entangled state between two identical wavefunctions, formulated as a bilinear combination of the spin states, analogous to the bipartite entanglement of two electrons. We then compute the entanglement entropy between two such universes, each described by spinorial wavefunctions. The analysis reveals that the entropy is maximized for specific combinations of the Misner variables (Omega _{i}) and (beta _{pm i}), with (i=I,II) labeling each universe. We interpret these maxima as configurations of maximal quantum correlation determined by the geometric size and anisotropy of the universes. The role of anisotropy in modulating the entanglement is also elucidated.

We study the properties of a nonlinear magnetic-charged black hole in the presence of a phantom global monopole. By incorporating nonlinear electrodynamics (NLE) and exotic scalar fields, we derive an exact black hole solution and analyze its geometric structure, causal properties, and thermodynamic behavior. We examine how the presence of a phantom global monopole modifies the black hole’s Hawking temperature, entropy, and stability conditions, revealing significant changes in its phase structure. Additionally, we investigate the geodesic motion of test particles. The quasinormal mode (QNM) spectrum is computed using the WKB approximation and Pöschl-Teller potential method, providing insights into the perturbative stability of the system. Furthermore, we analyze the grey-body factors that characterize radiation emission, highlighting their dependence on black hole parameters. Our findings indicate that the interplay between phantom energy, NLE, and global monopoles introduces observable deviations in strong-field astrophysical phenomena. These results offer potential signatures for testing modified gravity theories and contribute to a deeper understanding of black hole physics in exotic field environments.