Primordial gravitational waves in inflationary braneworld

TL;DR

This paper investigates how primordial gravitational waves generated during inflation are affected in the Randall-Sundrum braneworld model, revealing energy-dependent modifications to their spectrum and a simple mapping to four-dimensional results.

Contribution

It introduces a toy model connecting two de Sitter branes to analyze the impact of Hubble parameter changes on gravitational wave spectra in braneworld inflation.

Findings

Low-energy amplitude matches four-dimensional predictions

High-energy fluctuations are enhanced due to zero-mode normalization

A simple mapping approximates the five-dimensional spectrum from four-dimensional results

Abstract

We study primordial gravitational waves from inflation in Randall-Sundrum braneworld model. The effect of small change of the Hubble parameter during inflation is investigated using a toy model given by connecting two de Sitter branes. We analyze the power spectrum of final zero-mode gravitons, which is generated from the vacuum fluctuations of both initial Kaluza-Klein modes and zero-mode. The amplitude of fluctuations is confirmed to agree with the four-dimensional one at low energies, whereas it is enhanced due to the normalization factor of zero-mode at high energies. We show that the five-dimensional spectrum can be well approximated by applying a simple mapping to the four-dimensional fluctuation amplitude.