Black universes with trapped ghosts

TL;DR

This paper constructs static, spherically symmetric black-universe solutions in general relativity with a minimally coupled scalar field that has a localized ghost region, potentially explaining the absence of observable ghosts.

Contribution

It introduces new black-universe models with trapped ghosts in general relativity, expanding previous solutions involving phantom fields or brane worlds.

Findings

Existence of static, spherically symmetric black-universe solutions with localized ghost regions.

The ghost field is confined to a small strong-field region, avoiding observable effects.

These models provide a potential explanation for the non-observation of ghosts in nature.

Abstract

A black universe is a nonsingular black hole where, beyond the horizon, there is an expanding, asymptotically isotropic universe. Such models have been previously found as solutions of general relativity with a phantom scalar field as a source of gravity and, without phantoms, in a brane world of RS2 type. Here we construct examples of static, spherically symmetric black-universe solutions in general relativity with a minimally coupled scalar field \phi whose kinetic energy is negative in a restricted strong-field region of space-time and positive outside it. Thus in such configurations a "ghost" is trapped in a small part of space, which may in principle explain why no ghosts are observed under usual conditions.