Wormholes and nonsingular spacetimes in Palatinif(R)gravity

Abstract

We reconsider the problem of f (R) theories of gravity coupled to Born-Infeld theory of electrodynamics formulated in a Palatini approach, where metric and connection are independent fields. By studying electrovacuum configurations in a static and spherically symmetric space-time, we find solutions which reduce to their Reissner-Nordström counterparts at large distances but undergo important non-perturbative modifications close to the center. Our new analysis reveals that the point-like singularity is replaced by a finite-size wormhole structure, which provides a geodesically complete and thus nonsingular space-time, despite the existence of curvature divergences at the wormhole throat. Implications of these results, in particular for the cosmic censorship conjecture, are discussed.

Geodesically complete BTZ-type solutions of 2 + 1 Born–Infeld gravity

“…Let us point out that the fact that the affine parameter for null geodesics diverges at the location of the wormhole throat means that the wormhole actually lies on the future (or past) boundary of the geometry and, therefore, cannot be reached in any finite affine time. This mechanism of resolution of spacetime singularities has been already observed in certain four dimensional f (R) models [51].…”

Classical resolution of black hole singularities via wormholes

“…We have shown here that only the former is physically relevant and can be achieved in classical geometric scenarios with nontrivial topology and satisfying all the energy conditions. Though our analysis has focused on a four-dimensional setting, our results are still valid in arbitrary dimensions, where exact analytical solutions with wormhole structure, which are geodesically complete, have been found [37] (we note that geodesic completeness via wormholes can also be achieved in certain metricaffine f (R) theories [38,39]). Higher dimensional models confirm that the resolution of black hole singularities is a highly non-perturbative phenomenon, the GR solution being an excellent approximation down to the very throat of the wormhole, where the geometry quickly changes to account for this topological structure.…”

Search for astrophysical rotating Ellis wormholes with x-ray reflection spectroscopy

“…There are currently no fundamental principles that can rule out the existence of similar structures, which are indeed allowed both in general relativity and in alternative theories of gravity under certain conditions (see, for instance, Refs. [6][7][8][9][10][11][12][13]). In the spirit that whatever is not forbidden can potentially exist, several authors have recently studied observational signatures to search for astrophysical WHs in the Universe [14][15][16][17][18][19][20][21][22][23].…”