Inhomogeneous String Cosmologies

TL;DR

This paper derives exact inhomogeneous and anisotropic cosmological solutions in string theory with dilaton and axion fields, revealing their evolution, asymptotic behavior, and how inhomogeneities decay over time.

Contribution

It provides new exact solutions with cylindrical symmetry in string cosmology, including their asymptotic and duality properties, extending known homogeneous models.

Findings

Solutions describe ever-expanding universes with initial singularities.

Inhomogeneities evolve as non-linear waves and attenuate over time.

Near the singularity, solutions have a Kasner-like form.

Abstract

We present exact inhomogeneous and anisotropic cosmological solutions of low-energy string theory containing dilaton and axion fields. The spacetime metric possesses cylindrical symmetry. The solutions describe ever-expanding universes with an initial curvature singularity and contain known homogeneous solutions as subcases. The asymptotic form of the solution near the initial singularity has a spatially-varying Kasner-like form. The inhomogeneous axion and dilaton fields are found to evolve quasi-homogeneously on scales larger than the particle horizon. When the inhomogeneities enter the horizon they oscillate as non-linear waves and the inhomogeneities attentuate. When the inhomogeneities are small they behave like small perturbations of homogeneous universes. The manifestation of duality and the asymptotic behaviour of the solutions are investigated.