Towards Inflation in String Theory

TL;DR

This paper examines the challenges of embedding brane inflation into string theory compactifications, highlighting how moduli stabilization often steepens the inflaton potential, and discusses conditions under which inflation remains feasible.

Contribution

It identifies the impact of superpotential stabilization on inflaton potential steepness and discusses specific conditions for successful brane inflation in string theory.

Findings

Moduli stabilization typically makes the inflaton potential too steep for inflation.

Warped compactifications can naturally produce flat inflaton potentials.

Certain conditions on volume stabilization and warping can allow inflation to succeed.

Abstract

We investigate the embedding of brane inflation into stable compactifications of string theory. At first sight a warped compactification geometry seems to produce a naturally flat inflaton potential, evading one well-known difficulty of brane-antibrane scenarios. Careful consideration of the closed string moduli reveals a further obstacle: superpotential stabilization of the compactification volume typically modifies the inflaton potential and renders it too steep for inflation. We discuss the non-generic conditions under which this problem does not arise. We conclude that brane inflation models can only work if restrictive assumptions about the method of volume stabilization, the warping of the internal space, and the source of inflationary energy are satisfied. We argue that this may not be a real problem, given the large range of available fluxes and background geometries in string theory.