Kantowski-Sachs String Cosmologies

We present new exact solutions of the low-energy-effective-action string equations with both dilaton φ and axion H fields non-zero. The background universe is of Kantowski-Sachs type. We consider the possibility of a pseudoscalar axion field h (H = eφ(dh)∗) that can be either time or space dependent. The case of time-dependent h reduces to that of a stiff perfect-fluid cosmology. For space-dependent h there is just one non-zero time-space-space component of the axion field H , and this corresponds to a distinguished direction in space which prevents the models from isotropising. Also, in the latter case, both the axion field H and its tensor potential B (H = dB) are dependent on time and space yet the energy-momentum tensor remains time-dependent as required by the homogeneity of the cosmological model. Typeset using REVTEX ∗E-mail:[email protected] †E-mail:[email protected] 1