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 semiclassical perturbation spectra in the dilaton, axion, and moduli fields in the pre-big-bang scenario. By constructing the unique -duality-invariant field perturbations for the axion and dilaton fields we derive -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 we find that the axion spectrum depends upon the expansion rate of the internal dimensions which allows scale-invariant spectra. We note that for the metric is nonsingular in the conformal frame in which the axion is minimally coupled.
- Received 17 January 1997
DOI:https://doi.org/10.1103/PhysRevD.56.874
©1997 American Physical Society