Novel black-bounce spacetimes: wormholes, regularity, energy conditions, and causal structure

TL;DR

This paper introduces new regular black hole spacetimes called black-bounce models, which include traversable wormholes and bounces, analyzing their regularity, energy conditions, and causal structures with several novel geometries.

Contribution

It develops a general framework for black-bounce spacetimes, providing new solutions with complex horizon structures and establishing theorems on regularity and energy conditions.

Findings

New black-bounce geometries with multiple horizons

Existence of extremal black-bounce solutions

Conditions under which energy criteria are satisfied or violated

Abstract

We develop a number of novel "black-bounce" spacetimes. These are specific regular black holes where the "area radius" always remains non-zero, thereby leading to a "throat" that is either timelike (corresponding to a traversable wormhole), spacelike (corresponding to a "bounce" into a future universe), or null (corresponding to a "one-way wormhole"). We shall first perform a general analysis of the regularity conditions for such a spacetime, and then consider a number of specific examples. The examples are constructed using a mass function similar to that of Fan--Wang, and fall into several particular cases, such as the original Simpson--Visser model, a Bardeen-type model, and other generalizations thereof. We shall analyse the regularity, the energy conditions, and the causal structure of these models. The main results are several new geometries, more complex than before, with two or more horizons, with the possibility of an extremal case. We shall derive a general theorem regarding static space-time regularity, and another general theorem regarding (non)-satisfaction of the classical energy conditions.