The Graceful Exit Problem in String Cosmology

TL;DR

This paper investigates the conditions under which string cosmology solutions can transition smoothly from inflationary to standard expansion phases, highlighting the limitations of potential effects and proposing conformal field theory methods for further insight.

Contribution

It demonstrates that potential effects alone cannot ensure a graceful exit from inflation in weak curvature regimes and suggests conformal field theory as a tool for definitive analysis.

Findings

Potential effects do not enable graceful exit in weak curvature regime.

Duality-related branches can evolve into each other under certain conditions.

Conformal field theory techniques may provide conclusive answers.

Abstract

Isotropic string cosmology solutions can be classified into two duality related branches: one can be connected smoothly to an expanding Friedman-Robertson-Walker Universe, the other describes accelerated inflation or contraction. We show that, if the dilaton potential has certain generic properties, the two branches can evolve smoothly into each other. We find, however, that just the effects of a potential do not allow for a graceful exit from accelerated inflation in the weak curvature regime. We explain how conformal field theory techniques could be used to give a decisive answer on whether graceful exit from accelerated inflation is possible at all.