paper

Axion perturbation spectra in string cosmologies

arXiv:hep-th/9809105 · doi:10.1016/S0370-2693(98)01322-7

Abstract

We discuss the semi-classical perturbation spectra produced in the massless fields of the low energy string action in a pre big bang type scenario. Axion fields may possess an almost scale-invariant spectrum on large scales dependent upon the evolution of the dilaton and moduli fields to which they are coupled. As an example we calculate the spectra for three axion fields present in a truncated type IIB model and show that they are related with at least one of the fields having a scale-invariant or red perturbation spectrum. In the simplest pre big bang scenario this may be inconsistent with the observed isotropy of the microwave background. More generally, relations between the perturbation spectra in low energy string cosmologies reflect the symmetries of the theory.

9 pages, latex with epsf, 1 figure. Revised estimate of amplitude of density perturbations and extended discussion of possible conflict with isotropy of cosmic microwave background. To appear in Physics Letters B

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