Density perturbations in the brane-world

TL;DR

This paper investigates how density perturbations in Randall-Sundrum brane-world cosmologies influence bulk Weyl curvature and modify the evolution of large-scale fluctuations, revealing deviations from standard general relativity during high-energy inflation.

Contribution

It demonstrates that bulk effects induce non-adiabatic modes and alter the evolution of large-scale perturbations in brane-world models, providing a closed system on the brane without solving bulk equations.

Findings

Bulk effects produce non-adiabatic modes.

Large-scale metric perturbation is not constant during high-energy inflation.

Perturbation evolution differs from standard GR during high-energy regimes.

Abstract

In Randall-Sundrum-type brane-world cosmologies, density perturbations generate Weyl curvature in the bulk, which in turn backreacts on the brane via stress-energy perturbations. On large scales, the perturbation equations contain a closed system on the brane, which may be solved without solving for the bulk perturbations. Bulk effects produce a non-adiabatic mode, even when the matter perturbations are adiabatic, and alter the background dynamics. As a consequence, the standard evolution of large-scale fluctuations in general relativity is modified. The metric perturbation on large-scales is not constant during high-energy inflation. It is constant during the radiation era, except at most during the very beginning, if the energy is high enough.