Extra-dimensional cosmology with domain-wall branes

TL;DR

This paper develops a consistent cosmological model with a finite-thickness domain-wall brane, revealing energy-dependent scale factors and potential deviations from the weak equivalence principle, with implications for constraining brane thickness.

Contribution

It introduces a field-theoretic domain-wall brane model that recovers standard cosmology in the thin limit and explores novel energy-dependent effects on the scale factor.

Findings

Scale factor depends on particle energy and species.

Standard brane cosmology results are recovered in the thin limit.

Potential bounds on brane thickness are discussed.

Abstract

We show how to define a consistent braneworld cosmology in a model in which the brane is constructed as a field-theoretic domain wall of finite thickness. The Friedmann, Robertson-Walker metric is recovered in the region of the brane, but, remarkably, with scale factor that depends on particle energy and on particle species, constituting a breakdown of the weak equivalence principle on sufficiently small scales. This unusual effect comes from the extended nature of particles confined to a domain-wall brane, and the fact that they feel an "average" of the bulk spacetime. We demonstrate how to recover the standard results of brane cosmology in the infinitely-thin brane limit, and comment on how our results have the potential to place bounds on parameters such as the thickness of domain-wall braneworlds.