A NEW CLASS OF SPATIALLY HOMOGENEOUS 4D STRING BACKGROUNDS

A new class of spatially homogeneous 4D string backgrounds, the chi(d ->) according to a recent classification, is presented. Leading-order solutions exist only for Bianci types chi = I, II, III, VI-1, VII0. Due to the presence of the H 3-form field, whose dual is necessarily along a principal direction of anisotropy, exact SO(3) isotropy is always broken, while the axion scalar breaks homogeneity as well. Nevertheless, FRW symmetry can be attained asymptotically for Bianchi-types I and VII0. There is always an initial singularity and no inflation, as briefly discussed along with other fundamental aspects of the solutions.