Pre-Big-Bang in String Cosmology

Abstract

The duality-type symmetries of string cosmology naturally lead to a pre-big-bang phase of accelerated evolution as dual counterpart of the decelerated expansion of standard cosmology. We discuss several properties of this scenario, including the possibility that tracks of the pre-big-bang may be found either in the spectrum of relic gravitons or in the distortion they induce on the cosmic microwave background.Comment: 36 pages (plus 1 table and 3 figures ava. upon request), CERN-TH.657