Graceful Exit in String Cosmology

TL;DR

This paper explores how classical and quantum corrections to string theory's effective action facilitate a smooth transition from early inflationary expansion to a standard cosmological phase, addressing the graceful exit problem.

Contribution

It demonstrates how specific classical and quantum corrections enable a stable high-curvature string phase and violation of energy conditions for a graceful exit in string cosmology.

Findings

Classical corrections stabilize high curvature phases.

Quantum corrections induce null energy condition violation.

A mechanism for transitioning to a decelerated universe is proposed.

Abstract

The graceful exit transition from a dilaton-driven inflationary phase to a decelerated Friedmann-Robertson-Walker era requires certain classical and quantum corrections to the string effective action. Classical corrections can stabilize a high curvature string phase while the evolution is still in the weakly coupled regime, and quantum corrections can induce violation of the null energy condition, allowing evolution towards a decelerated phase.