Evolution of Fluctuations during Graceful Exit in String Cosmology

TL;DR

This paper investigates how fluctuations evolve during a graceful exit in string cosmology, revealing enhancements in curvature and gravitational waves, along with short wavelength instabilities, impacting primordial spectrum predictions.

Contribution

It introduces a detailed analysis of fluctuation evolution during the graceful exit in string cosmology, highlighting new instability phenomena and their implications.

Findings

Enhanced curvature perturbations and gravitational waves during graceful exit

Identification of short wavelength instability post-exit

Implications for primordial spectrum from string cosmology

Abstract

We study the evolution of fluctuations in a universe dominated by a scalar field coupled to the Gauss-Bonnet term. During the graceful exit, we found non-negligible enhancements of both curvature perturbation and gravitational wave in the long wavelength limit, and we also found a short wavelength instability for steep background superinflation just after the completion of the graceful exit. This result for one possible graceful exit mechanism would provide a significant implication on the primordial spectrum from the string cos mology.