Brane Inflation

TL;DR

The paper proposes a novel inflation mechanism in brane-worlds with TeV-scale gravity, where inflation is driven by the relative separation of branes and described in four dimensions by a slowly rolling brane mode with a flat plateau potential. Large e-foldings arise from the weak brane-brane interactions at large separations, and inflation ends when branes collide, with reheating localized on the branes to avoid bulk graviton overproduction. Density perturbations are analyzed under the unusually small Hubble scale, suggesting possible brane-localized origins and highlighting the need for extremely flat potentials; baryogenesis could proceed via non-thermal or inflaton-decay channels to brane baryons. The approach emphasizes naturalness in the brane-world setting but remains highly model-dependent, hinging on moduli stabilization, SUSY breaking, and the spectrum of light bulk modes, with implications for whether the electroweak Higgs can serve as the inflaton.

Abstract

We present a novel inflationary scenario in theories with low scale (TeV) quantum gravity, in which the standard model particles are localized on the branes whereas gravity propagates in the bulk of large extra dimensions. This inflationary scenario is natural in the brane world picture. In the lowest energy state, a number of branes sit on top of each other (or at an orientifold plane), so the vacuum energy cancels out. In the cosmological setting, some of the branes "start out" relatively displaced in the extra dimensions and the resulting vacuum energy triggers the exponential growth of the 3 non-compact dimensions. The number of e-foldings can be very large due to the very weak brane-brane interaction at large distances. In the effective four-dimensional field theory, the brane motion is described by a slowly rolling scalar field with an extremely flat plateau potential. When branes approach each other to a critical distance, the potential becomes steep and inflation ends rapidly. Then the branes "collide" and oscillate about the equilibrium point, releasing energy mostly into radiation on the branes.