Warping the Weak Gravity Conjecture

• Main Authors: Karta Kooner, Susha Parameswaran, Ivonne Zavala
• Format: Article
• Language: English
• Published: Elsevier 2016-08-01
• Series: Physics Letters B
• Subjects: String theory; Cosmology; Inflation; D-branes; Warped geometries; Large axion decay constants
• Online Access: http://www.sciencedirect.com/science/article/pii/S0370269316302374
• ISSN: 0370-2693; 1873-2445

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 a probe D-brane in a warped throat. We show that warped geometries can allow the requisite super-Planckian axion decay constant to be achieved, within the supergravity approximation and consistently with the Weak Gravity Conjecture. Preliminary estimates of the brane backreaction suggest that the probe approximation may be under control. 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.