Enhancement of axion decay constants in type IIA theory?

Abstract

We investigate the possibility of enhancement of the 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 nonperturbative effects included to ensure stabilization of all moduli). In this setup, we attempt to obtain the 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 alignment mechanism. We do not find super-Planckian effective decay constants by either of the approaches. Furthermore, we find that the alignment angle of the Kim-Nilles-Peloso mechanism cannot be made arbitrarily small by adjusting the fluxes.