Bianchi Type I Cosmologies in Arbitrary Dimensional Dilaton Gravities

TL;DR

This paper investigates Bianchi type I cosmologies within arbitrary dimensional dilaton gravity, deriving exact solutions and analyzing how dilaton potentials influence anisotropy and isotropization in the universe.

Contribution

It provides exact parametric solutions for Bianchi type I models in dilaton gravity with exponential potentials, highlighting conditions for isotropization.

Findings

Exact solutions expressed in parametric form

Dilaton potential influences anisotropy evolution

Universe isotropizes only with dilaton potential or deficit charge

Abstract

We study the low energy string effective action with an exponential type dilaton potential and vanishing torsion in a Bianchi type I space-time geometry. In the Einstein and string frames the general solution of the gravitational field equations can be expressed in an exact parametric form. Depending on the values of some parameters the obtained cosmological models can be generically divided into three classes, leading to both singular and nonsingular behaviors. The effect of the potential on the time evolution of the mean anisotropy parameter is also considered in detail, and it is shown that a Bianchi type I Universe isotropizes only in the presence of a dilaton field potential or a central deficit charge.