Gauss-Bonnet modified gravity models with bouncing behavior

TL;DR

This paper explores how adding a Gauss-Bonnet term to gravity models can produce new cosmological solutions, including bouncing universes and unified dark energy models with various phases, relevant for early and late universe evolution.

Contribution

It introduces novel Gauss-Bonnet modified gravity models that unify bouncing behavior and accelerated expansion, with analysis of their stability and physical properties.

Findings

New models exhibit bouncing behavior in early universe

Models unify phantom, quintessence, and matter phases

Solutions are stable and consistent with cosmological observations

Abstract

The following issue is addressed: how the addition of a Gauss-Bonnet term (generically coming from most fundamental theories, as string and M theories), to a viable model, can change the specific properties, and even the physical nature, of the corresponding cosmological solutions? Specifically, brand new original dark energy models are obtained in this way with quite interesting properties, which exhibit, in a unified fashion, the three distinguished possible cosmological phases corresponding to phantom matter, quintessence, and ordinary matter, respectively. A model, in which the equation of state parameter, $w$, is a function of time, is seen to lead either to a singularity of the Big Rip kind or to a bouncing solution which evolves into a de Sitter universe with $w=-1$. Moreover, new Gauss-Bonnet modified gravity models with bouncing behavior in the early stages of the universe evolution are obtained and tested for the validity and stability of the corresponding solutions. They allow for a remarkably natural, unified description of a bouncing behavior at early times and accelerated expansion at present.