Cuscuton Bounce

TL;DR

This paper demonstrates that cuscuton gravity allows for a regular cosmological bounce without instabilities or ghosts, by breaking the usual link between bounce and Null Energy Condition violation.

Contribution

It introduces a toy model showing how cuscuton modifications enable stable bounces, a novel approach avoiding typical instabilities in bouncing cosmologies.

Findings

Cuscuton gravity permits regular bounces without ghosts.

The model breaks the link between bounce and Null Energy Condition violation.

The approach provides a proof of concept for stable bouncing cosmologies.

Abstract

In general relativity producing a regular bounce entails violation of Null Energy Condition for a dynamical source in the model. That generically indicates existence of ghosts or other instabilities. However, in cuscuton modification of gravity, the correspondence between a background bounce and violation of Null Energy Condition for dynamical sources is broken. Cuscuton is an Infra Red modification and it can make the background go through a regular bounce. At the same time, since it does not contain any dynamical degrees of freedom, it does not lead to ghosts or other instabilities. Here, we present a toy scenario of a regular bouncing cosmology and prove this claim. Our model is presented as a proof of concept at this point and does not aim to explain observations in late time cosmology.