Inflation on the brane with vanishing gravity

Abstract

Many existing models of brane inflation suffer from a steep irreducible gravitational2 potential between the branes that causes inflation to end too early. Inspired by the fact that point masses in 2+1 D exert no gravitational force, we propose a novel unwarped and non-supersymmetric setup for inflation, consisting of 3-branes in two extra dimensions compactified on a sphere. The size of the sphere is stabilized by a combination of a bulk cosmological constant and a magnetic flux. Computing the 4D effective potential between probe branes in this background, we find a non-zero contribution only from exchange of level-1 KK modes of the graviton and radion. For antipodal pairs of branes the contribution from these modes is absent; we can thus eliminate entirely the troublesome gravitational contribution to the inflationary potential.