Non-stationary wormholes with the presence of scalar fields and modified gravity

TL;DR

This paper constructs non-stationary wormhole and cosmological spacetimes using scalar fields and modified gravity, addressing singularities and ghost issues through constraints and alternative theories.

Contribution

It introduces a novel method to generate regular non-stationary wormholes and cosmologies, eliminating ghost fields via constraints and exploring f(R) gravity as an alternative.

Findings

Regular non-stationary wormholes constructed

Ghost scalar fields can be eliminated by constraints

New wormhole solutions found in f(R) gravity

Abstract

Some novel regular spacetimes are considered that show a non-stationary wormhole structure. A Simpson-Visser-like procedure is applied to reconstruct these regular spacetimes, free of time-like and space-like singularities. Such a procedure is also applied to describe a regular cosmological expansion, where the universe reaches a minimum scale and then rebounds. This type of regular spacetime is achieved by considering some scalar fields as sources, with the appropriate kinetic term and scalar potential. We show that all these sources turn out to be ghosts due to the wrong sign of the kinetic term. These ghosts can, however, be eliminated by constraints. Nevertheless, the same procedure is also explored in the framework of modified gravities, particularly within the so-called f(R) gravity, where a new wormhole spacetime is also obtained that does not require a ghost scalar field.