ANISOTROPIC GENERALIZATIONS OF THE FRW STRING BACKGROUNDS

An entire class of non-isotropic generalizations of the FRW string backgrounds is presented, essentially supplying the string-cosmology counterpart of the diagonal Bianchi-type models in general relativity. Leading-order solutions with vanishing cosmological constant and time-depended axion/dilaton scalars have been found for all types. They include as special cases all hitherto known solutions within this class, while the limits of SO(3) isotropy supply all possible FRW backgrounds. There is always an initial singularity and no inflation. Other features of the solutions which can illuminate the impact of spatial anisotropies on the dynamics of the early universe, as well as their behaviour under abelian T-duality, are discussed.