A Model of Graceful Exit in String Cosmology

TL;DR

This paper presents a novel string cosmology model demonstrating a smooth transition from an inflationary phase to a standard cosmological era, highlighting the role of quantum corrections and null energy condition violations.

Contribution

It introduces the first model of graceful exit in string cosmology that incorporates classical and quantum corrections to achieve a decelerated universe transition.

Findings

Classical corrections can stabilize high curvature string phases.

Quantum corrections that violate the null energy condition enable transition to decelerated expansion.

Stabilizing the dilaton may require turning off quantum corrections, possibly via non-perturbative effects.

Abstract

We construct, for the first time, a model of graceful exit transition from a dilaton-driven inflationary phase to a decelerated Friedman-Robertson-Walker era. Exploiting a demonstration that classical corrections can stabilize a high curvature string phase while the evolution is still in the weakly coupled regime, we show that if additional terms of the type that may result from quantum corrections to the string effective action exist, and induce violation of the null energy condition, then evolution towards a decelerated Friedman-Robertson-Walker phase is possible. We also observe that stabilizing the dilaton at a fixed value, either by capture in a potential minimum or by radiation production, may require that these quantum corrections are turned off, perhaps by non-perturbative effects or higher order contributions which overturn the null energy condition violation.