Primordial fluctuations in bulk inflaton model

TL;DR

This paper presents an exact analytical study of primordial fluctuations in a brane inflation model driven by a bulk inflaton, revealing unique features in scalar and tensor perturbations at high energies.

Contribution

It introduces a family of exact solutions for bulk inflaton-driven inflation and analyzes the resulting primordial fluctuation spectra, highlighting differences from brane-localized inflaton models.

Findings

Scalar and tensor perturbation amplitudes are enhanced at high inflation energy scales.

The ratio of scalar to tensor perturbations remains unsuppressed at high energies.

Massive Kaluza-Klein modes become significant at high frequencies.

Abstract

An inflationary brane model driven by a bulk inflaton with exponential potential is proposed. We find a family of exact solutions that describe power-law inflation on the brane. These solutions enable us to derive exact solutions for metric perturbations analytically. By calculating scalar and tensor perturbations, we obtain a spectrum of primordial fluctuations at the end of the inflation. The amplitudes of scalar and tensor perturbations are enhanced in the same way if the energy scale of the inflation is sufficiently higher than the tension of the brane. Then the relative amplitude of scalar and tensor perturbations is not suppressed even for high-energy inflation. This is a distinguishable feature from the inflation model driven by inflaton on the brane where tensor perturbations are suppressed for high-energy inflation. We also point out that massive Kaluza-Klein modes are not negligible at high-frequencies on 3-space of our brane.