General Relativity and Gravitation最新文献

This study explores a covariant extension of the Proca framework, incorporating nonlinear terms for a massive spin-1 field while ensuring consistency and ghost-free behavior. Coupled with gravity, this effective extended Proca-Nuevo model provides viable cosmological solutions, constrained by Big Bang Nucleosynthesis observations. By enforcing ( |Delta T_f / T_f| < 4.7 times 10^{-4} ), the model parameter (Lambda ) is restricted to the range ( Lambda in left( -2.80025 times 10^{-4}, , 2.80025 times 10^{-4}right) ). This correction supports a consistent description of the Big Bang Nucleosynthesis era, effectively aligning the freeze-out temperature predictions with observational bounds and the constrained Hubble function predicting accelerated expansion across all redshifts. These findings highlight the potential of extended Proca-Nuevo theories in bridging modified gravity and Effective Field Theory, providing the aspects of early-time cosmology.

We study the interaction between gravitational waves and a quantum two-level system consisting of a spin 1/2 particle using the formalism of the proper detector frame. This approach highlights the effects of gravitational waves on both the particles and the observer, emphasizing that only relative measurements can be made. Specifically, within this framework, the gravitational field of the waves is described using the gravitoelectromagnetic analogy. The interaction of the system is then determined by the gravitomagnetic field of the wave, which induces a time-dependent perturbation. We analyze this perturbation for both generic frequencies and resonance conditions, and discuss its implications.

Mukkamala and Pereñiguez recently discovered a new master function for even-parity metric perturbations of the Schwarzschild spacetime. Remarkably, this function satisfies the Regge–Wheeler equation (instead of the Zerilli equation), which was previously understood to govern the odd-parity sector of the perturbation only. In this paper I follow up on their work. First, I identify a source term for their Regge–Wheeler equation, constructed from the perturbing energy-momentum tensor. Second, I relate the new master function to the radiation fields at future null infinity and the event horizon. Third, I reconstruct the metric perturbation from the new master function, in the Regge–Wheeler gauge. The main conclusion of this work is that the greater simplicity of the Regge–Wheeler equation (relative to the Zerilli equation) is offset by a greater complexity of obtaining the radiation fields and reconstructing the metric.

This article delves into the observational signatures and theoretical underpinnings of rotating astrophysical objects, with a particular focus on superspinars -exotic objects characterized by preventing the formation of event horizons due to their high angular momentum. While solutions within General Relativity (Kerr superspinars) predict such objects, their classical forms harbor naked singularities, violate causality, and exhibit problematic repulsive gravitational effects. These characteristics render classical superspinars theoretically objectionable, leading to the consideration of them as physically implausible. On the other hand, the incompatibility between General Relativity and Quantum Mechanics suggests the exploration of alternative models, particularly those in which Quantum Gravity dominates the core and prevents the formation of scalar curvature singularities. This work demonstrates that superspinars without scalar curvature singularities can avoid all the complications associated with Kerr superspinars. Moreover, from a phenomenological standpoint, it is shown that the silhouettes of these superspinars could be markedly distinct from those of black holes and classical Kerr superspinars. To substantiate these differences, we perform a comprehensive analysis of inner null geodesics and investigate the structure of the Planckian region within superspinars without scalar curvature singularities. Our study reveals that only these superspinars provide the potential for distant observers to directly observe the extremely high curvature regions within their interiors.

By considering the analytic, static and spherically symmetric solution for the Schwarzschild black holes immersed in dark matter fluid with non-zero tangential pressure (Jusufi in Eur Phys J C 83:103, 2023) and Hernquist-type density profiles (Cardoso in Phys Rev D 105:L061501, 2022), we compute the luminosity of accretion disk. We study the circular motion of test particles in accretion disk and calculate the radius of the innermost stable circular orbits. Using the steady-state Novikov-Thorne model we also compute the observational characteristics of such black hole’s accretion disk and compare our results with the usual Schwarzschild black hole in the absence of dark matter fluid. We find that the tangential pressure plays a significant role in decreasing the size of the innermost stable circular orbits and thus increases the luminosity of black hole’s accretion disk.

The conference Black Holes Inside and Out marked the 50th anniversary of Hawking’s seminal paper on black hole radiance. It was clear already from Hawking’s analysis that a proper quantum gravity theory would be essential for a more complete understanding of the evaporation process. This task was undertaken in loop quantum gravity (LQG) 2 decades ago and by now the literature on the subject is quite rich. The goal of this contribution is to summarize a mainstream perspective that has emerged. The intended audience is the broader gravitational physics community, rather than quantum gravity experts. Therefore, the emphasis is on conceptual issues, especially on the key features that distinguish the LQG approach, and on concrete results that underlie the paradigm that has emerged. This is not meant to be an exhaustive review. Rather, it is a broad-brush stroke portrait of the present status. Further details can be found in the references listed.

In this paper, we consider the spherically symmetric gravitational collapse of isotropic matter undergoing dissipation in the form of heat flux, with a generalized Vaidya exterior, in the context of f(R, T) gravity. Choosing (f(R, T)=R+2lambda T), and applying the f(R, T) junction conditions on the field equations for the interior and exterior regions, we have obtained matching conditions of the matter-Lagrangian and its derivatives across the boundary. The time of formation of singularity and the time of formation of apparent horizon have been determined and constraints on the integration constants are examined for which the final singularity is hidden behind the horizon.

Various generalizations of the scalar, axisymmetric “horizon hair” for extremal black holes have recently appeared in the literature. In this paper, we propose an expression for a non-axisymmetric gravitational “charge” and its potentially observable imprint at a finite distance from the horizon (Ori-coefficient) in extremal Kerr black hole backgrounds. Using a hyperboloidal foliation, we offer strong and robust numerical evidence for the potential existence of this horizon hair and its properties. Specifically, we consider the time evolution of horizon penetrating, quadrupolar and (subdominant) octupolar gravitational perturbations with compact support on extremal Kerr (EK) spacetime. We do this by numerically solving the Teukolsky equation and determining the conserved charge values on the horizon and at a finite distance from the black hole.

In this paper, we consider families of solutions for excited states of Proca stars in spherical symmetry. We focus on the first two excited configurations and perform a series of fully non-linear dynamical simulations in order to study their properties and stability. Our analysis reveals that excited Proca stars are always unstable against even very small perturbations, and their dynamical evolution can lead to three different final states: collapse to a black hole, dissipation, or migration to a different configuration in the ground state. We find that migration to the ground state can only occur in a small region of the parameter space of solutions with negative binding energy.

In recent papers, Fuentealba, Henneaux, and Troessaert (FHT) gave definitions for supertranslation invariant Lorentz charges in the ADM Hamiltonian formalism and showed that their definitions match with the Chen, Wang, Yau (CWY) definitions of Lorentz charges at null infinity which are free from “supertranslation ambiguities”. In this brief note, motivated by the analysis of FHT, we write expressions for the supertranslation invariant Lorentz charges in Beig–Schmidt variables at spacelike and timelike infinity. We present calculations, building upon the work of Compère, Gralla, and Wei (CGW), to show that our expressions for supertranslation invariant Lorentz charges match the CWY definitions at null infinity.