Bouncing Universes in String-inspired Gravity

TL;DR

This paper explores how higher-derivative, ghost-free modifications to gravity inspired by string theory can lead to bouncing cosmological models that avoid singularities by weakening gravity at short distances.

Contribution

It introduces a novel class of asymptotically free, ghost-free gravity models that enable non-singular bouncing cosmologies.

Findings

Gravity weakens at short distances due to higher-derivative modifications.

Pressure effects can prevent cosmological singularities.

A bouncing universe solution is achieved without ghosts.

Abstract

We consider the effects on cosmology of higher-derivative modifications of (effective) gravity that make it asymptotically free without introducing ghosts. The weakening of gravity at short distances allows pressure to prevent the singularity, producing a solution with contraction preceding expansion.