Classical inhomogeneities in string cosmology

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Abstract
We generalize previous work on inhomogeneous pre-big bang cosmology by including the effect of nontrivial moduli and antisymmetric-tensor–axion fields. The general quasihomogeneous 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.