ANISOTROPIC SPACETIMES IN HOMOGENEOUS STRING COSMOLOGY

The dynamics of the early universe may have been profoundly influenced by spatial anisotropies. A search for such backgrounds in the context of string cosmology has uncovered the existence of an entire class of 4D spatially homogeneous but not necessarily isotropic spacetimes, analogous to the class of Bianchi-type models in general relativity. Leading-order solutions with vanishing cosmological constant but with non-vanishing dilaton and antisymmetric field are explicitly found for all types. This is a new class of solutions, whose isotropy limits reproduce all known and, further, all possible FRW-type of models in the string effective-action context considered. There is always an initial singularity and no inflation, Other features of the general solutions, including their behavior under abelian T duality are also discussed.