Scalar perturbations in Randall-Sundrum braneworld cosmology

TL;DR

This paper investigates how scalar perturbations evolve in Randall-Sundrum braneworld cosmology during the radiation era, revealing scale-dependent amplification effects that could influence primordial black hole formation.

Contribution

It provides a numerical analysis of coupled bulk and brane wave equations, confirming large-scale spectrum similarity to GR and identifying small-scale amplification effects.

Findings

Density perturbations with small wavelengths are amplified during horizon re-entry.

Large-scale spectrum matches general relativity predictions.

Potential implications for primordial black hole formation.

Abstract

We study the evolution of scalar perturbations in the radiation-dominated era of Randall-Sundrum braneworld cosmology by numerically solving the coupled bulk and brane master wave equations. We find that density perturbations with wavelengths less than a critical value (set by the bulk curvature length) are amplified during horizon re-entry. Conversely, we explicitly confirm from simulations that the spectrum is identical to GR on large scales. Although this magnification is not relevant for the cosmic microwave background or measurements of large scale structure, it may have some bearing on the formation of primordial black holes in Randall-Sundrum models.