Accidental Inflation in String Theory

TL;DR

This paper demonstrates that inflation driven by the volume modulus in type IIB string theory can occur naturally near flat points of the potential, with tunable spectral index and negligible gravitational waves, within the racetrack model framework.

Contribution

It introduces a string theory inflation model based on the KL moduli stabilization, showing how flat points support slow-roll inflation with specific spectral properties.

Findings

Spectral index range 0.93 to 1, tunable by potential shape.

Negligible primordial gravitational waves, r < 10^{-6}.

Inflation occurs near flat hill-top or inflection points in the potential.

Abstract

We show that inflation in type IIB string theory driven by the volume modulus can be realized in the context of the racetrack-based Kallosh-Linde model (KL) of moduli stabilization. Inflation here arises through the volume modulus slow-rolling down from a flat hill-top or inflection point of the scalar potential. This situation can be quite generic in the landscape, where by uplifting one of the two adjacent minima one can turn the barrier either to a flat saddle point or to an inflection point supporting eternal inflation. The resulting spectral index is tunable in the range of 0.93 < n_s < 1, and there is only negligible production of primordial gravitational waves r < 10^{-6}. The flatness of the potential in this scenario requires fine-tuning, which may be justified taking into account the exponential reward by volume factors preferring the regions of the universe with the maximal amount of slow-roll inflation. This consideration leads to a tentative prediction of the spectral index $n_s\approx 0.95$ or $n_s \approx 0.93$ depending on whether the potential has a symmetry phi -> - phi or not.