Rotational Perturbations in Neveu-Schwarz-Neveu-Schwarz String Cosmology

TL;DR

This paper analyzes first-order rotational perturbations in NS-NS string cosmology models, showing how the dilaton potential influences the decay of cosmic rotation, with exact solutions found for specific potentials.

Contribution

It identifies the specific dilaton potentials that allow for exact solutions of rotational decay in NS-NS string cosmology models.

Findings

Rotation decays rapidly with a potential U, or arbitrarily if U=0.

Exact analytic solutions for rotation functions are obtained.

Potential form U restricts rotational behavior in the models.

Abstract

First order rotational perturbations of the flat Friedmann-Robertson-Walker (FRW) metric are considered in the framework of four dimensional Neveu-Schwarz-Neveu-Schwarz (NS-NS) string cosmological models coupled with dilaton and axion fields. The decay rate of rotation depends mainly upon the dilaton field potential U. The equation for rotation imposes strong limitations upon the functional form of U, restricting the allowed potentials to two: the trivial case U=0 and a generalized exponential type potential. In these two models the metric rotation function can be obtained in an exact analytic form in both Einstein and string frames. In the potential-free case the decay of rotational perturbations is governed by an arbitrary function of time while in the presence of a potential the rotation tends rapidly to zero in both Einstein and string frames.