Non-Singular Cosmological Models in String Gravity with Second Order Curvature Corrections

TL;DR

This paper explores non-singular cosmological solutions within string gravity incorporating second-order curvature corrections, analyzing how modulus field potentials influence the avoidance of singularities and the universe's chaotic dynamics.

Contribution

It provides explicit analytical non-singular asymptotic solutions in string-inspired gravity models with Gauss-Bonnet terms, highlighting conditions under which singularities are avoided.

Findings

Exponentially steep coupling functions from string theory do not permit non-singular past asymptotics unless the modulus potential vanishes at infinity.

Certain modulus potentials preserve non-singular behavior despite the presence of curvature corrections.

The Gauss-Bonnet term modifies chaotic dynamics in closed FRW universes.

Abstract

We investigate FRW cosmological solutions in the theory of modulus field coupled to gravity through a Gauss-Bonnet term. The explicit analytical forms of nonsingular asymptotics are presented for power-law and exponentially steep modulus coupling functions. We study the influence of modulus field potential on these asymptotical regimes and find some forms of the potential which do not destroy the nonsingular behavior. In particular, we obtain that exponentially steep coupling functions arising from the string theory do not allow nonsingular past asymptotic unless modulus field potential tends to zero for modulus field $\psi \to \pm \infty$. Finally, the modification of the chaotic dynamics in the closed FRW universe due to presence of the Gauss-Bonnet term is discussed.