# Enhancement of axion decay constants in type IIA theory?

## TL;DR

This paper explores the potential for enhancing axion decay constants within type IIA string theory compactifications, but finds limitations in achieving super-Planckian values through known mechanisms.

## Contribution

It provides a detailed analysis of axion decay constant enhancement attempts in string theory, including flux adjustments and the KNP alignment mechanism, revealing fundamental constraints.

## Key findings

- No super-Planckian decay constants found
- Alignment angle cannot be arbitrarily small
- Flux adjustments do not enable large decay constants

## Abstract

We investigate the possibility of enhancement of effective axion decay constant in well controlled constructions in string theory. To this end, we study the dynamics of axions arising in the compactifications of type IIA string theory on Calabi-Yau orientifolds with background fluxes (with non-perturbative effects included to ensure stabilization of all moduli). In this setup, we attempt to obtain large effective axion decay constant in two different ways: by searching for a direction in field space in which the potential is sufficiently flat and by arriving at a very explicit stringy embedding of the Kim-Nilles-Peloso (KNP) alignment mechanism. We do not find super-Planckian effective decay constants by either of the approaches. Furthermore, we find that the alignment angle of KNP mechanism can not be made arbitrarily small by adjusting the fluxes.