Chaotic inflation on the brane - art. no. 041301

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