Vacuum fluctuations in axion-dilaton cosmologies
Abstract
We study axion-dilaton cosmologies derived from the low-energy string effective action. We present the classical homogeneous Friedmann-Robertson-Walker solutions and derive the semi-classical perturbation spectra in the dilaton, axion and moduli fields in the pre-Big Bang scenario. By constructing the unique S-duality invariant field perturbations for the axion and dilaton fields we derive S-duality invariant solutions, valid when the axion field is time-dependent as well as in a dilaton-vacuum cosmology. Whereas the dilaton and moduli fields have steep blue perturbation spectra (with spectral index n=4) we find that the axion spectrum depends upon the expansion rate of the internal dimensions (0.54<n<4) which allows scale-invariant (n=1) spectra. We note that for n<1 the metric is non-singular in the conformal frame in which the axion is minimally coupled.
Keywords
Cite
@article{arxiv.hep-th/9701082,
title = {Vacuum fluctuations in axion-dilaton cosmologies},
author = {E. J. Copeland and Richard Easther and David Wands},
journal= {arXiv preprint arXiv:hep-th/9701082},
year = {2009}
}
Comments
LaTeX, 23 pages plus 6 figures, minor typos corrected and references updated. To appear in Phys Rev D