Inflationary string cosmology backgrounds can amplify perturbations in a more
efficient way than conventional inflationary backgrounds, because the
perturbation amplitude may grow - instead of being constant - outside the
horizon. If not gauged away, the growing mode can limit the range of validity
of a linearized description of perturbations. Even in the restricted linear
range, however, this enhanced amplification may lead to phenomenological
consequences unexpected in the context of the standard inflationary scenario.
In particular, the production of a relic graviton background strong enough to
be detected in future by LIGO, and/or the generation of a stochastic
electromagnetic background strong enough to seed the cosmic magnetic fields and
to be responsible for the observed large scale anisotropy.Comment: 25 pages, Plain TEX, 3 figures available by fax upon request, to
appear in "Proc. of the 3rd Colloque Cosmologie" (Observatoire de Paris,7-9
June 1995
