Aligned Natural Inflation in the Large Volume Scenario

TL;DR

This paper embeds natural inflation within a string theory framework using the Large Volume Scenario, employing axion alignment to achieve large decay constants compatible with cosmological constraints.

Contribution

It provides a explicit string theory model of natural inflation with aligned axions, satisfying multiple theoretical and observational constraints.

Findings

Successful realization of aligned axion inflation in a string compactification.

Compatibility with the weak gravity conjecture and scalar perturbation constraints.

Heavy bulk axions with stabilized volumes in relatively small geometries.

Abstract

We embed natural inflation in an explict string theory model and derive observables in cosmology. We achieve this by compactifying the type IIB string on a Calabi-Yau orientifold, stabilizing moduli via the Large Volume Scenario, and configuring axions using D7-brane stacks. In order to obtain a large effective decay constant, we employ the Kim-Nilles-Peloso alignment mechanism, with the required multiple axions arising naturally from anisotropic bulk geometries. The bulk volumes, and hence the axion decay constants, are stabilized by generalized one-loop corrections and subject to various conditions: the K\"ahler cone condition on the string geometry; the convex hull condition of the weak gravity conjecture; and the constraint from the power spectrum of scalar perturbations. We find that all constraints can be satisfied in a geometry with relatively small volume and thus heavy bulk axion mass. We also covariantize the convex hull condition for the axion-dilaton-instanton system and verify the normalization of the extremal bound.