Signatures of Brane Inflation

TL;DR

This paper investigates brane inflation in a five-dimensional setting, accounting for graviton emission energy loss, which affects inflation dynamics and the evolution of curvature perturbations on superhorizon scales.

Contribution

It derives the energy loss term due to graviton emission and develops a method to track superhorizon perturbations, highlighting deviations from standard inflationary predictions.

Findings

Energy loss from graviton emission influences inflation dynamics.

Superhorizon curvature perturbations are not conserved in this model.

A new methodology for calculating the power spectrum is proposed.

Abstract

We study slow-roll inflation on a three-brane in a five-dimensional bulk where the effects of energy loss from the brane due to graviton emission is included in a self-consistent manner. We explicitly derive the form of the energy loss term due to inflaton-to-graviton scattering and thus determine the precise dynamics of the two resulting inflationary solutions. What is also remarkable is that nonconservation of energy on the brane causes the curvature perturbation to not be conserved on superhorizon scales even for the purely adiabatic perturbations produced in single-field inflation. Thus the standard method of calculating the power spectrum of inflaton fluctuations at Hubble exit and equating it to the power spectrum at horizon reentry no longer holds. The superhorizon evolution of the perturbations must be tracked from horizon exit through to when the modes reenter the horizon for the late time power spectrum to be calculated. We develop the methodology to do this in this paper as well.