Chaotic inflation on the brane

TL;DR

This paper explores how brane-world modifications to gravity influence chaotic inflation, leading to enhanced inflation, a scale-invariant spectrum, and allowing inflation at sub-Planckian field values.

Contribution

It demonstrates that brane-induced gravity significantly alters chaotic inflation dynamics, enabling inflation at lower field values and producing a scale-invariant spectrum.

Findings

Enhanced Hubble expansion at high energies

Inflation occurs at sub-Planckian field values

Perturbations approach a scale-invariant spectrum

Abstract

We consider slow-roll inflation in the context of recently proposed four-dimensional effective gravity induced on the world-volume of a three-brane in five-dimensional Einstein gravity. We find significant modifications of the simplest chaotic inflationary scenario when the five-dimensional Planck scale is below about 10^{17} GeV. We use the comoving curvature perturbation, which remains constant on super-Hubble scales, in order to calculate the spectrum of adiabatic density perturbations generated. Modifications to the Friedmann constraint equation lead to a faster Hubble expansion at high energies and a more strongly damped evolution of the scalar field. This assists slow-roll, enhances the amount of inflation obtained in any given model, and drives the perturbations towards an exactly scale-invariant Harrison-Zel'dovich spectrum. In chaotic inflation driven by a massive scalar field we show that inflation can occur at field values far below the four-dimensional Planck scale, though above the five-dimensional fundamental scale.