S-duality in String Gas Cosmology

TL;DR

This paper explores a string theory cosmological model where S-duality invariance stabilizes the dilaton and suggests a new mechanism for moduli fixing, with potential cosmological implications involving a decreasing Hubble radius.

Contribution

It introduces a toy model with (m,n) string modes demonstrating S-duality invariance and a novel dilaton stabilization mechanism in string gas cosmology.

Findings

Dilaton is stabilized via S-duality invariance.

A possible cosmological phase with decreasing Hubble radius is proposed.

The model offers a new approach to moduli fixing in string cosmology.

Abstract

We consider a toy cosmological model in string theory involving the winding and momentum modes of (m,n) strings, i.e. bound states of m fundamental and n D-strings. The model is invariant under S-duality provided that m and n are interchanged. The dilaton is naturally stabilized due to S-duality invariance, which offers a new mechanism of moduli fixing in string gas cosmology. Using a tachyon field rolling down to its ground state, we also point out a possible way of realizing a cosmological phase with decreasing Hubble radius and constant dilaton.