Rotational perturbations in Neveu-Schwarz-Neveu-Schwarz string cosmology -art. no. 104013

First order rotational perturbations of the fiat Friedmann-Robertson-Walker metric are considered in the framework of four dimensional Neveu-Schwarz-N eveu-Schwarz string cosmological models coupled with dilaton and axion fiel ds. For the H field we use the solitonic ansatz, assuming that it is a func tion of time only. The decay rate of rotation depends mainly upon the dilat on field potential U. The equation for rotation imposes strong limitations upon the functional form of U, restricting the allowed potentials to two: t he trivial case U=0 and a generalized exponential type potential. In these two models the metric rotation function can be obtained in an ex;lct analyt ic form in both Einstein and string frames. In the potential-free case the decay of rotational perturbations is governed by an arbitrary function of t ime while in the presence of a potential the rotation tends rapidly to zero in both Einstein and string frames.