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Vacuum fluctuations in axion-dilaton cosmologies

E. J. Copeland·Richard Easther·David Wands
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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.

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E. J. Copeland, Richard Easther, David Wands. 1997-05-27. Vacuum fluctuations in axion-dilaton cosmologies. https://doi.org/10.1103/physrevd.56.874

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