Constraints on pre-big bang models for seeding large-scale anisotropy by massive Kalb-Ramond axions

Abstract

We discuss the conditions under which pre-big bang models can fit the observed large-scale anisotropy with a primordial spectrum of massive (Kalb--Ramond) axion fluctuations. The primordial spectrum must be sufficiently flat at low frequency and sufficiently steeper at high frequency. For a steep and/or long enough high-frequency branch of the spectrum the bounds imposed by COBE's normalization allow axion masses of the typical order for a Peccei--Quinn--Weinberg--Wilczek axion. We provide a particular example in which an appropriate axion spectrum is obtained from a class of backgrounds satisfying the low-energy string cosmology equations.

Comments: 11 pages, revtex, two figures included using epsfig. An updated collection of papers on the pre-big bang scenario is available at http://www.to.infn.it/~gasperin