Tensor perturbations in high-curvature string backgrounds

Abstract

We derive a generalized equation for the evolution of tensor perturbations in a cosmological background, taking into account higher-curvature contributions and a tree-level coupling to the dilaton in the string frame. The equation is obtained by perturbing the gravi-dilaton string effective action, expanded up to first order in ${\alpha }^{\prime }$. The ${\alpha }^{\prime }$ corrections can modify the low-energy perturbation spectrum, but the modifications are shown to be small when the background curvature keeps constant in the string frame.

Comments: 9 pages, REVTEX, three figures included using EPSFIG. An updated collection of papers on the pre-big bang scenario in string cosmology is a available at http://www.to.infn.it/teorici/gasperini