S-brane to thermal non-singular string cosmology

TL;DR

This paper introduces a new class of non-singular string cosmologies featuring a bouncing universe, a maximal temperature, and controlled string interactions, connecting contracting and expanding phases through a critical transition.

Contribution

It presents explicit non-singular string cosmological models with a bounce, thermal phases, and evolving dilaton, based on a novel class of thermal superstring vacua with gravito-magnetic fluxes.

Findings

Universe remains non-singular throughout evolution.

String coupling stays below critical value, ensuring weak interactions.

Cosmology exhibits a smooth bounce connecting contracting and expanding phases.

Abstract

We present a new class of non-singular string cosmologies in d space-time dimensions. At very early times, \tau << \tau_c, the Universe is described by a flat \sigma-model metric, a constant maximal temperature T_c and super-weak string interactions, g_str << 1. During the evolution, the metric remains flat up to \tau_c, while the string coupling grows and reaches a critical value g*_str at \tau_c. This phase is characterized by a uniform temporal distribution of spacelike branes. At later times, \tau > \tau_c, the Universe enters in a new phase of expansion, with radiation. The string coupling decreases due to the dilaton motion and asymptotes to a constant for \tau >> \tau_c. Throughout the evolution, the string coupling remains smaller than g*_str. In the Einstein frame, the cosmologies describe bouncing Universes, where two distinct phases are connected at \tau_c. In the initial contracting phase, the evolution of the scale factor is identical to that of a negatively curved Universe filled with radiation. At later times, the Universe enters in an expanding thermal phase with a running dilaton. Explicit examples are presented in a large class of thermal (4,0) type II superstring vacua, with non-trivial "gravito-magnetic" fluxes.