Anisotropy dissipation in brane-world inflation

TL;DR

This paper investigates anisotropic brane-world cosmology during inflation, revealing that large initial anisotropy can enhance inflation and decay rapidly, broadening initial conditions for universe formation.

Contribution

It demonstrates that large anisotropy does not hinder inflation in brane-world models and introduces a transient anisotropic phase, extending previous general relativity results.

Findings

Large initial anisotropy increases inflationary damping.

Anisotropy decays rapidly during inflation.

Initial quasi-isotropic expansion for large kinetic scalar fields.

Abstract

We examine the behavior of an anisotropic brane-world in the presence of inflationary scalar fields. We show that, contrary to naive expectations, a large anisotropy does not adversely affect inflation. On the contrary, a large initial anisotropy introduces more damping into the scalar field equation of motion, resulting in greater inflation. The rapid decay of anisotropy in the brane-world significantly increases the class of initial conditions from which the observed universe could have originated. This generalizes a similar result in general relativity. A unique feature of Bianchi I brane-world cosmology appears to be that for scalar fields with a large kinetic term the initial expansion of the universe is quasi-isotropic. The universe grows more anisotropic during an intermediate transient regime until anisotropy finally disappears during inflationary expansion.