Anisotropic four-dimensional Neveu-Schwarz-Neveu-Schwarz string cosmology

An anisotropic (Bianchi type I) cosmology is considered in the four-dimensional Neveu-Schwarz-Neveu-Schwarz (NS-NS) sector of low-energy effective string theory coupled to a dilaton and an axionlike H field within a de Sitter-Einstein frame background. The general solution of the gravitational field equations can be expressed in an exact parametric form in both Einstein and string frames. The study of the time dynamics of this universe leads to the conclusion that in the absence of a dilaton field potential or a cosmological constant the initial anisotropies do not decay and the time evolution of a pure dilaton and axion field filled Bianchi type I space-time does not lead to an isotropic phase.