Duality in String Cosmology

TL;DR

This paper explores duality symmetries in string cosmology, particularly scale factor duality, and their implications for non-singular pre-big-bang scenarios, higher derivative corrections, and particle spectra.

Contribution

It introduces a new duality symmetry for inhomogeneity perturbations, linking it to S- and T-duality, and analyzes its effects on cosmological models and particle production.

Findings

Scale factor duality suggests a non-singular pre-big-bang cosmology.

A new duality symmetry for perturbations reproduces known particle spectra.

The symmetry provides bounds on particle production in cosmological backgrounds.

Abstract

Scale factor duality, a truncated form of time dependent T-duality, is a symmetry of string effective action in cosmological backgrounds interchanging small and large scale factors. The symmetry suggests a cosmological scenario ("pre-big-bang") in which two duality related branches, an inflationary branch and a decelerated branch are smoothly joined into one non-singular cosmology. The use of scale factor duality in the analysis of the higher derivative corrections to the effective action, and consequences for the nature of exit transition, between the inflationary and decelerated branches, are outlined. A new duality symmetry is obeyed by the lowest order equations for inhomogeneity perturbations which always exist on top of the homogeneous and isotropic background. In some cases it corresponds to a time dependent version of S-duality, interchanging weak and strong coupling and electric and magnetic degrees of freedom, and in most cases it corresponds to a time dependent mixture of both S-, and T-duality. The energy spectra obtained by using the new symmetry reproduce known results of produced particle spectra, and can provide a useful lower bound on particle production when our knowledge of the detailed dynamical history of the background is approximate or incomplete.