Magnetic wormholes and black universes with invisible ghosts

TL;DR

This paper constructs explicit, regular solutions in general relativity featuring traversable wormholes and black universes using scalar and electromagnetic fields, introducing 'invisible ghosts' to mitigate instability issues associated with phantom fields.

Contribution

It introduces the concept of 'invisible ghosts', phantom scalar fields that decay rapidly, enabling stable, regular wormhole and black universe solutions without observable negative-energy regions.

Findings

Solutions include various numbers of horizons, from zero to four.

'Invisible ghosts' reduce instability issues compared to traditional phantom fields.

Constructed models exhibit flat and AdS asymptotics.

Abstract

We construct explicit examples of globally regular static, spherically symmetric solutions in general relativity with scalar and electromagnetic fields describing traversable wormholes with flat and AdS asymptotics and regular black holes, in particular, black universes. (A black universe is a regular black hole with an expanding, asymptotically isotropic space-time beyond the horizon.) The existence of such objects requires invoking scalars with negative kinetic energy ("phantoms", or "ghosts"), which are not observed under usual physical conditions. To account for that, the so-called "trapped ghosts" were previously introduced, i.e., scalars whose kinetic energy is only negative in a restricted strong-field region of space-time and positive outside it. This approach leads to certain problems, including instability (as is illustrated here by derivation of an effective potential for spherical pertubations of such systems). In this paper, we use for model construction what we call "invisible ghosts", i.e., phantom scalar fields sufficiently rapidly decaying in the weak-field region. The resulting configurations contain different numbers of Killing horizons, from zero to four.