General Relativity and Gravitation最新文献

Kerr–Vaidya metrics are the simplest dynamical axially-symmetric solutions, all of which violate the null energy condition and thus are consistent with the formation of a trapped region in finite time according to distant observers. We examine different classes of Kerr–Vaidya metrics, and find two which possess spherically-symmetric counterparts that are compatible with the finite formation time of a trapped region. These solutions describe evaporating black holes and expanding white holes. We demonstrate a consistent description of accreting black holes based on the ingoing Kerr–Vaidya metric with increasing mass, and show that the model can be extended to cases where the angular momentum to mass ratio varies. For such metrics we describe conditions on their dynamical evolution required to maintain asymptotic flatness.Pathologies are also identified in the evaporating white hole geometry in the form of an intermediate singularity accessible by timelike observers. We also describe a generalization of the equivalence between Rindler and Schwarzschild horizons to Kerr–Vaidya black holes, and describe the relevant geometric constructions.

We investigate the topological implications of stable minimal surfaces existing in a static perfect fluid space while ensuring that the fluid satisfies certain energy conditions. Based on the main findings, the topology of the level set ({f=c}) (the boundary of a stellar model) is studied, where c is a positive constant and f is the static potential of a static perfect fluid space. Bounds for the Hawking mass for the level set ({f=c}) of a static perfect fluid space are derived. Consequently, we prove an inequality that resembles the Penrose inequality for compact and non-compact static perfect fluid spaces, guaranteeing that the Hawking mass is positive for a class of surfaces in a static perfect fluid space. We will present a section dedicated to examples of static stellar models, one of them inspired by Witten’s black hole (or Hamilton’s cigar).

This brief review, intended for high energy and astrophysics researchers, explores the implications of recent theoretical advances in string theory and the Swampland program for understanding bounds on the structure of positive potentials allowed in quantum gravity. This has a bearing on both inflationary models for the early universe as well as the fate of our universe. The paper includes a review of the dS conjecture as well as the TransPlanckian Censorship Conjecture and its relation to the species scale. We provide evidence for these principles as well as what they may lead to in terms of phenomenological predictions.

I consider the algebra of operators along the world line of an observer as a background independent algebra in quantum gravity.

We compute analytically differential curvature invariants for accelerating, rotating and charged black holes with a cosmological constant (varLambda ). Specifically, we compute novel closed-form expressions for the Karlhede and the Abdelqader-Lake invariants, for accelerating Kerr–Newman black holes in (anti-)de Sitter spacetime or subsets thereof with the aim of detecting physically relevant surfaces, like horizons and ergospheres. We explicitly show that some of the computed invariants of the particular class of spacetimes are vanishing at the event, Cauchy and acceleration horizons or ergosurface. Using the Bianchi identities we calculate in the Newman-Penrose tetrad formalism in closed-form the Page-Shoom curvature invariant for the general class of accelerating, rotating and charged Plebański-Demiański black holes with (varLambda not =0) and we prove that is zero at the relevant surfaces. For the invariants that vanish at horizon radii we show that are non-zero everywhere else, or in the case there are additional roots such roots do not affect their capability to detect the physically relevant surfaces. Such curvature invariants are locally measurable quantities and thus could allow the local experimental detection of the event and acceleration horizons or outer ergosurface. The differential invariants which are norms associated with the gradients of the first two Weyl invariants, are explored in detail. Although both locally single out the horizons, their global behaviour is also intriguing. Both reflect the background angular momentum and electric charge as the volume of space allowing a timelike gradient decreases with increasing spin and charge.

A well-known soliton (bubble) solution of five-dimensional Kaluza–Klein General Relativity is modified by imposing mass on the scalar field. By forcing the scalar field to be short-range, the failure of the original bubble solution to satisfy the equivalence principle is remedied, and the bubble acquires gravitational mass. Most importantly, the mass is quantized, even in this classical setting, and has a value (m_P / (4 sqrt{alpha })), where (m_P) is the Planck mass, and (alpha ) is the fine-structure constant. This result applies for any choice of scalar-field mass, as it is an attractor for the field equations.

In this paper, we have put forwarded a detailed investigation on the cosmic evolution of Bianchi type III model within the realm of Born-Infeld f(R) gravity executing the Palatini approach. Using a very eminent tool known as Dynamical System Approach (DSA), we have curtailed the complexity of the non linear field equations and study the dynamics for the form (f(R) =R-beta / R^n). The main focus of our work is to retrieve the sequence of cosmic evolution and to study the evolution of shear as well as spatial curvature.

Here, we will discuss some ideas for possible classical/semi-classical modifications of the black hole solutions in General Relativity (GR). These modifications/extensions include black holes in higher dimensions; black holes with additional gravitational fields, or fields beyond the Standard Model of Particle Physics; black holes in alternative classical theories of gravity and in semiclassical gravity; phenomenological models that extend the GR black hole solutions.

We study the dynamics of a charged radiating star in general relativity. The junction conditions at the surface of the star lead to a restriction that connects the radial pressure to the heat flux. The master equation reduces to a nonlinear second order differential equation which determines the temporal evolution. The dynamical behaviour is studied via a phase plane analysis which reveals interesting behaviour. The presence of both the electromagnetic field and the cosmological constant are included in our treatment. They affect the temporal evolution of the gravitating star. We identify the restrictions on the parameters that lead to a stable asymptotic end state of the star.