A regular center instead of a black bounce

TL;DR

This paper develops methods to modify spherically symmetric space-times to have a regular center, avoiding singularities, and applies these methods to various solutions including Fisher and dilatonic black holes, within the framework of general relativity.

Contribution

It introduces new algorithms for creating regular centers in general spherically symmetric solutions, extending previous work to more general space-times and matter sources.

Findings

Regular centers achieved for Fisher (JNW) solutions.

Regular modifications obtained for dilatonic black holes.

Scalar field sources can be non-phantom outside the regular center.

Abstract

The widely discussed ``black-bounce'' mechanism of removing a singularity at $r=0$ in a spherically symmetric space-time, proposed by Simpson and Visser, consists in removing the point $r=0$ and its close neighborhood, resulting in emergence of a regular minimum of the spherical radius that can be a wormhole throat or a regular bounce. Instead, it has been recently proposed to make $r=0$ a regular center by properly modifying the metric, still preserving its form in regions far from $r=0$. Different algorithms of such modifications have been formulated for a few classes of singularities. The previous paper considered space-times whose Ricci tensor satisfies the condition $R^t_t =R^r_r$, and regular modifications were obtained for the Schwarzschild, Reissner-Nordstr\"om metrics, and two examples of solutions with magnetic fields obeying nonlinear electrodynamics (NED). The present paper considers regular modifications of more general space-times, and as examples, modifications with a regular center have been obtained for the Fisher (also known as JNW) solution with a naked singularity and a family of dilatonic black holes. Possible field sources of the new regular metrics are considered in the framework of general relativity (GR), using the fact that any static, spherically symmetric metric with a combined source involving NED and a scalar field with some self-interaction potential. This scalar field is, in general, not required to be of phantom nature (unlike the sources for black bounces), but in the examples discussed here, the possible scalar sources are phantom in a close neighborhood of $r=0$ and are canonical outside it.