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

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