On the initial regime of pre-big bang cosmology

TL;DR

This paper explores how a pre-big bang cosmological phase with growing string coupling can produce the right spectrum of curvature perturbations, consistent with an initial string-vacuum state, without being limited by backreaction effects.

Contribution

It demonstrates that a viable, slightly red spectrum of scalar perturbations can originate from an asymptotic, perturbative pre-big bang regime compatible with initial string-vacuum conditions.

Findings

A perturbative pre-big bang phase can produce the observed curvature perturbation spectrum.

The initial string-vacuum state supports an extended pre-big bang phase without backreaction limitations.

The model aligns with the Asymptotic Past Triviality hypothesis.

Abstract

The production of a background of super-horizon curvature perturbations with the appropriate (red) spectrum needed to trigger the cosmic anisotropies observed on large scales is associated, in the context of pre-big bang inflation, with a phase of growing string coupling. The extension towards the past of such a phase is not limited in time by the dynamical backreaction of the quantum perturbations of the cosmological geometry and of its sources. A viable, slightly red spectrum of scalar perturbations can thus be the output of an asymptotic, perturbative regime which is well compatible with an initial string-vacuum state satisfying the postulate of "Asymptotic Past Triviality".