Scalar perturbations in 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 scalar perturbations in braneworld cosmology, showing scale-dependent amplification during horizon re-entry not predicted by general relativity.

Findings

Small-scale density perturbations are amplified during horizon re-entry.

Large-scale spectrum remains identical to general relativity.

Implications for primordial black hole formation in braneworld models.

Abstract

We study the behaviour 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. This means that the radiation era matter power spectrum will be at least an order of magnitude larger than the predictions of general relativity (GR) on small scales. 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 will have some bearing on the formation of primordial black holes in Randall-Sundrum models.