Cosmological bounces and Lorentzian wormholes in Galileon theories with an extra scalar field

TL;DR

This paper investigates the feasibility of constructing bouncing cosmologies and Lorentzian wormholes within cubic Galileon theories with an extra scalar, finding fundamental instabilities that prevent their stable realization.

Contribution

It demonstrates that stable classical bouncing cosmologies and wormholes cannot be achieved in these theories due to inherent instabilities and ghost issues.

Findings

Bouncing models exhibit gradient instabilities.

Wormhole backgrounds always contain ghosts.

Abstract

We study whether it is possible to design a "classical" spatially flat bouncing cosmology or a static, spherically symmetric asymptotically flat Lorentzian wormhole in cubic Galileon theories interacting with an extra scalar field. We show that bouncing models are always plagued with gradient instabilities, while there are always ghosts in wormhole backgrounds.