Back Reaction and Graceful Exit in String Inflationary Cosmology

TL;DR

This paper demonstrates that quantum back reaction in a two-dimensional string cosmology model can connect super-inflation and FRW phases smoothly, potentially solving the graceful exit problem in string inflation.

Contribution

It provides an exactly solvable model showing how quantum effects can prevent singularities and enable a smooth transition between inflationary phases in string cosmology.

Findings

Quantum back reaction delays curvature growth.

Smooth transition between super-inflation and FRW phases.

Potential resolution of the graceful exit problem.

Abstract

Classical string cosmology consists of two branches related to each other by scale-factor duality: a super-inflation branch and a Friedmann-Robertson-Walker (FRW) branch. Curvature and string coupling singularity separates the two branches, hence posing `graceful exit problem' to super-inflationary string cosmology. In an exactly soluble two-dimensional compactification model it is shown that quantum back reaction retards curvature and string coupling growth and connects the super-inflation branch to the FRW branch without encountering a singularity. This may offer an attractive solution to the `graceful exit problem' in string inflationary cosmology.