Warping the Weak Gravity Conjecture

TL;DR

This paper demonstrates that warping in string theory can enable super-Planckian axion decay constants necessary for Natural Inflation, challenging the constraints imposed by the Weak Gravity Conjecture.

Contribution

It shows that warping allows for large axion decay constants in string models, addressing previous limitations and exploring the tension with string scale requirements.

Findings

Warping enables super-Planckian axion decay constants.

High string scale is difficult to achieve with large field inflation.

Results challenge the constraints of the Weak Gravity Conjecture.

Abstract

The Weak Gravity Conjecture, if valid, rules out simple models of Natural Inflation by restricting their axion decay constant to be sub-Planckian. We revisit stringy attempts to realise Natural Inflation, with a single open string axionic inflaton from D-branes in a warped throat. We show that warping allows the requisite super-Planckian axion decay constant to be achieved consistently with the Weak Gravity Conjecture. However, there is a tension between large axion decay constant and high string scale, where the requisite high string scale is difficult to achieve in all attempts to realise large field inflation using perturbative string theory. We comment on the Generalized Weak Gravity Conjecture in the light of our results.