Spherical collapse of small masses in the ghost-free gravity

Abstract

Abstract:We discuss some properties of recently proposed models of a ghost-free gravity. For this purpose we study solutions of linearized gravitational equations in the framework of such a theory. We mainly focus on the version of the ghost-free theory with the exponential modification exp( /µ 2 ) −1 of the free propagator. The following three problems are discussed: (i) gravitational field of a point mass; (ii) Penrose limit of a point source boosted to the speed of light; and (iii) spherical gravitational collapse of null fluid. For the first problem we demonstrate that it can be solved by using the method of heat kernels and obtain a solution in a spacetime with arbitrary number of dimensions. For the second problem we also find the corresponding gyraton-type solutions of the ghost-free gravitational equations for any number of dimensions. For the third problem we obtain solutions for the gravitational field for the collapse of both "thin" and "thick" spherical null shells. We demonstrate how the ghost-free modification of the gravitational equations regularize the solutions of the linearized Einstein equations and smooth out their singularities.

Nonlocal gravity in D dimensions: Propagators, entropy, and a bouncing cosmology

“…In Refs. [26,27], the authors have shown that the spherical collapse within a linearised limit does not form a curvature singularity in this class of models.…”

Quantum radiation from a sandwich black hole

“…Quanta, propagating near it, experience huge blueshift and B is the corresponding blueshift factor. Using this fact one can estimate the total energy of the radiation, emitted from the inner horizon as follows 20) where ∆E 0 is a scale-invariant value of the energy, which is of the order of 1.…”

“…Similar theory appears naturally also in the context of noncommutative geometry deformation of the Einstein gravity [11,12] (see a review [13] and references therein). The application of the ghost free theory of gravity to the problem of singularities in cosmology and black holes can be found in [14][15][16][17][18][19][20][21][22][23][24][25][26][27]. In spite of a number of promising results, we still do not have a final conclusive solution of this problem in the ghost-free gravity.…”

Finite entanglement entropy of black holes

“…Notice, that the content of this section is general and independent on the particular solution as long as it shows an event horizon. Therefore, we can for example apply our analysis to any black hole solution, singular [44] or singularity-free [33][34][35][36][37][38][39][40][41][42][43]. Moreover, as we remarked in the introduction, our results can be easily exported to local higher derivative theories [60,75], where in the conditions stipulated above, we are sure that the Schwarzschild metric is an exact black hole solution.…”

“…In section II we briefly introduce a class of weakly non-local theories of gravity, which are unitary (ghost-free) and perturbatively super-renormalizable or finite in the quantum field theory framework [9][10][11][12][13][14][15][16][17][18][19][20][21][22]. At classical level evidences endorse that we are dealing with "singularity-free gravitational " the-ories [33][34][35][36][37][38][39][40][41] (see also the recent papers [42,43]). However, the Einstein spaces seem still to be exact solutions of the nonlocal theory [44,45], although it is still a debated open problem what kind of energy tensor could source such spacetimes in a non-local theory [46].…”