Axion decay constants at special points in type II string theory

TL;DR

This paper explores how quantum and geometric corrections at special points in moduli space can lower the axion decay constant below the string scale in type II string theory, with implications for phenomenology.

Contribution

It introduces a mechanism to decouple the axion decay constant from the string scale using corrections at special moduli space points.

Findings

Axion decay constant can be significantly lower than the string scale.

Special points in moduli space, like small complex structure points, influence the decay constant.

Moduli stabilization can lead to low-scale axion decay constants.

Abstract

We propose the mechanism to disentangle the decay constant of closed string axion from the string scale in the framework of type II string theory on Calabi-Yau manifold. We find that the quantum and geometrical corrections in the prepotential that arise at some special points in the moduli space widen the window of axion decay constant. In particular, around the small complex structure points, the axion decay constant becomes significantly lower than the string scale. We also discuss the moduli stabilization leading to the phenomenologically attractive low-scale axion decay constant.