Cosmological Solutions of Higher-Curvature String Effective Theories with Dilatons

TL;DR

This paper investigates how higher-curvature corrections in string theory effective actions influence cosmological solutions, revealing that such solutions vanish with the dilaton unless string-loop effects are considered.

Contribution

It provides a comprehensive analysis of higher-curvature effects on cosmology across various string theories, highlighting the role of the dilaton and loop effects.

Findings

Cosmological solutions exist without dilaton for all string types.

Including the dilaton causes these solutions to disappear.

String-loop effects can restore the solutions.

Abstract

We study the effect of higher-curvature terms in the string low-energy effective actions on the cosmological solutions of the theory, up to corrections quartic in the curvatures, for the bosonic and heterotic strings as well as the type II superstring. We find that cosmological solutions exist for all string types but they always disappear when the dilaton field is included, a conclusion that can be avoided if string-loop effects are taken into account.