Classical Inhomogeneities in String Cosmology

TL;DR

This work extends inhomogeneous pre-big bang string cosmology to include non-trivial moduli and axion/B-field content, deriving quasi-homogeneous asymptotic solutions and estimating the duration of the perturbative inflationary phase from perturbative initial data. By working in both string and Einstein frames, it reveals remnants of T- and S-duality in the asymptotic solutions and presents explicit axion-dilaton-modulus configurations with controlled gradient expansions. The analysis shows that a large class of patches naturally inflates, yielding a quasi-flat, homogeneous phase, while identifying a Milne-type attractor in the far past for sufficiently isotropic data and outlining the limits of validity of the low-energy effective action. The results illuminate how two classical moduli—the onset string coupling and curvature—govern the amount of perturbative PBB inflation and contribute to understanding the broader viability and challenges of the pre-big bang scenario, including the exit problem.

Abstract

We generalize previous work on inhomogeneous pre-big bang cosmology by including the effect of non-trivial moduli and antisymmetric-tensor/axion fields. The general quasi-homogeneous asymptotic solution---as one approaches the big bang singularity from perturbative initial data---is given and its range of validity is discussed, allowing us to give a general quantitative estimate of the amount of inflation obtained during the perturbative pre-big bang era. The question of determining early-time ``attractors'' for generic pre-big bang cosmologies is also addressed, and a motivated conjecture is advanced. We also discuss S-duality-related features of the solutions, and speculate on the way an asymptotic T-duality symmetry may act on moduli space as one approaches the big bang.

Figures (1)

• Figure 1: Approximate flow diagram from the early-time attractor to the singularity.