General Relativity and Gravitation最新文献

In this article, we theoretically construct a (2 + 1)-dimensional rotating thin shell wormhole using the Darmois-Israel junction formalism. This thin shell wormhole whose validity has been checked by analyzing the energy conditions, specifically, the weak and null energy conditions, is actually constructed by cutting and pasting two rotating hairy black hole spacetimes in (2+1)-dimensions. We further discuss different physical features of the constructed wormhole, viz., the nature of the gravitational field, the equation of state at the throat, and the time evolution of the throat radius. We also analyze the stability of the thin shell wormhole by investigating the equation of motion under small perturbations.

Do compact objects other than black holes and neutron stars exist in the universe? Do all black holes conform with the predictions of Einstein’s General Relativity? Do classical black holes exist at all? Future gravitational-wave observations and black-hole imaging might shed light on these foundational questions and deepen our understanding of the dark cosmos.

This study explores the dynamics and phase-space behavior of a multi-component dark energy model, where the dark sector consists of a minimally coupled canonical scalar field and the cosmological constant, using a dynamical system analysis setup for various types of potential for which a general parameterization of the scalar field potentials has been considered. Several fixed points with different cosmological behaviors have been identified. A detailed stability analysis has been done and possible late-time attractors have been found. For this multi-component dark energy model, the late-time attractors are either fully dominated by the cosmological constant or represent a scenario where a combination of the scalar field and the cosmological constant dominates the universe. In this type of model, there is a possibility that the scalar field can become dynamical quite early compared to the standard era of dark energy domination. However, our analysis indicates that this early time contribution of the scalar field occurs deep in the matter-dominated era, not before the recombination era.

To consider the inevitable cosmic magnetic effects instead of the unknown dark sector of matter/energy on the inflation phase of the expanding universe some authors have proposed several extended exotic Einstein–Maxwell gravities which are addressed in this work. Some of these exotic models include directional interaction terms between the electromagnetic vector field and the metric tensor field. We use one of them to investigate the physical effects of interaction terms on the thermodynamic behavior of the modified Reissner–Nordstrom (RN) black hole. We use the perturbation series method to find analytic solutions of the field equations because of the non-linearity of the field equations which cause they do not have analytic closed form solutions. We investigate possibility of the Hawking–Page and the small/large black hole phase transition and also, effects of the interaction part of the model on possibility of the coexistence of the several phases of the perturbed AdS RN black hole under consideration.

General relativity and quantum field theory are the cornerstones of our understanding of physical processes, from subatomic to cosmic scales. While both theories work remarkably well in their tested domains, they show minimal overlap. However, our research challenges this separation by revealing that non-perturbative effects bridge these distinct domains. We introduce a novel mechanism wherein, at linear order, spin-2 fields around an arbitrary background acquire effective mass due to the spontaneous symmetry breaking (SSB) of either global or local symmetry of complex scalar field minimally coupled to gravity. The action of the spin-2 field is identical to the extended Fierz-Pauli (FP) action, corresponding to the mass deformation parameter (alpha = 1/2). We show that this occurs due to the effect of SSB on the variation of the energy-momentum tensor of the matter field, which has a dominant effect during SSB. The extended FP action has a salient feature, compared to the standard FP action: the action has 6 degrees of freedom with no ghosts. For local U(1) SSB, we establish that the effective mass of spin-2 fields is related to the mass of the gauge boson and the electric charge of the complex scalar field. Interestingly, our results indicate that the millicharged dark matter scalar fields, generating dark photons, can produce a mass of spin-2 fields of the same order as the Hubble constant ((H_0)). Hence, we argue that the dark sector offers a natural explanation for the acceleration of the current Universe.

This work provides a spacetime interpretation of the confluent Heun functions within black hole perturbation theory (BHPT) and explores their relationship to the hyperboloidal framework. In BHPT, the confluent Heun functions are solutions to the radial Teukolsky equation, but they are traditionally studied without an explicit reference to the underlying spacetime geometry. Here, we show that the distinct behaviour of these functions near their singular points reflects the structure of key geometrical surfaces in black hole spacetimes. By interpreting homotopic transformations of the confluent Heun functions as changes in the spacetime foliation, we connect these solutions to different regions of the black hole’s global structure, such as the past and future event horizons, past and future null infinity, spatial infinity, and even past and future timelike infinity. We also discuss the relationship between the confluent Heun functions and the hyperboloidal formulation of the Teukolsky equation. Although neither confluent Heun form of the radial Teukolsky equation can be interpreted as hyperboloidal slices, this approach offers new insights into wave propagation and scattering from a global black hole spacetime perspective.

Entangled Relativity is a non-linear reformulation of Einstein’s General Theory of Relativity (General Relativity) that offers a more parsimonious formulation. This non-linear approach notably requires the simultaneous definition of matter fields, thus aligning more closely with Einstein’s principle of relativity of inertia than General Relativity does. Solutions for spherically charged black holes have already been identified. After exploring further some of the properties of these solutions, we present new solutions for the field equations pertaining to slowly rotating charged black holes.

We conduct studies on Levin’s taxonomy of periodic orbits for neutral test particles around a Reissner-Nordström naked singularity. It was known that naked singularities could harbor two distinct regions of time-like bound orbits and thus we expect periodic orbits to appear in both regions. It is possible for a pair of periodic orbits from both regions to possess the exact same angular momentum L and energy E values. We chart the sets of periodic orbits in (L, E)-parameter space and highlight the general distribution pattern of these sets for three possible scenarios. Regions within (L, E)-space can be partitioned into multiple domains ({mathcal {D}}_k) based on the roots configuration of the quartic polynomial P(u) where u is the inverse radial coordinate. Consequently, each domain and interestingly enough, portions of certain periodic orbits sets that lie in different ({mathcal {D}}_k) require different analytical solutions to plot the resulting orbit. Furthermore, we uncover physical properties of some hypothetical circular orbits residing in the inner region from analysing the (L, E)-space.

It is well-known that the Kretschmann curvature diverges strongly at the classical singularity of the black hole interior. In this paper, we are therefore interested in whether such a strong divergence can be tamed quantum mechanically in the vicinity of the black hole singularity. For this purpose, we consider DeWitt-regular quantum black hole solutions of a self-adjoint Wheeler–DeWitt equation originating from a Kantowski-Sachs representation of the black hole interior, coupled with a Klein–Gordon field that accounts for the existence of zero-point quantum vacuum fluctuations. We find that there exist regular quantum black holes with self-adjoint Hamiltonians having well-behaved Kretschmann curvature in the vicinity of the singularity, tamed by stronger restrictions on the eigenvalues than ones required by the DeWitt boundary condition. Consequently, the Kretschmann-regular black holes are found in smaller but still infinite domains in the space of eigenvalues allowed by the DeWitt criterion. Furthermore, we find that other relevant classically diverging quantities pose no threat as their quantum mechanical counterparts are well-behaved in the vicinity of the singularity.

Ehlers, Pirani, and Schild argued that measurements of null and timelike geodesics yield Weyl and projective connections, respectively, with compatibility in the lightlike limit giving an integrable Weyl connection. Their conclusions hold only for a 4-dim representation of the conformal connection on the null cone, and by restricting reparameterizations of timelike geodesics to yield a torsion-free, affine connection. An arbitrary connection gives greater freedom. A linear connection for the conformal symmetry of null geodesics requires the SO(4,2) representation. The enlarged class of projective transformations of timelike geodesics changes Weyl’s projective curvature, and we find invariant forms of the torsion and nonmetricity, along with a new, invariant, second rank tensor field generalizing the dilatational curvature without requiring a metric. We show that either projective or conformal connections require a monotonic, twice differentiable function on a spacetime region foliated by order isomorphic, totally ordered, twice differentiable timelike curves in a necessarily Lorentzian geometry. We prove that the conditions for projective and conformal Ricci flatness imply each other and gauge choices within either can reduce the geometry to the original Riemannian form. Thus, measurements of null and timelike geodesics lead to an SO(4,2) connection, with no requirement for a lightlike limit. Reduction to integrable Weyl symmetry can only follow from the field equations of a gravity theory. We show that the simplest quadratic spacetime action leads to this reduction.