Towards Universal Axion Inflation and Reheating in String Theory

TL;DR

This work embeds axion-driven inflation into type IIB string theory within the LVS, aiming to realize large-field inflation compatible with a sizable tensor-to-scalar ratio. It develops two realizations using the universal axion: a natural inflation model where the axion potential arises from magnetized $E3$-instantons (or related F-term effects), and an axion monodromy model where fluxes break the axion shift symmetry to yield an effectively quadratic potential. In both cases the inflaton is the universal axion, with a well-defined mass hierarchy set by the overall volume $\mathcal{V}$, and a mechanism ensuring reheating predominantly into Standard Model fields via brane-localized couplings. The constructions require a moderately large compactification volume ($\mathcal{V}\sim 10^{2}-10^{3}$) and face UV concerns such as $f>M_{\rm pl}$ implying $g_s>1$, but they provide a concrete UV-complete path to inflation that connects high-energy string dynamics to observable cosmology and post-inflationary reheating.

Abstract

The recent BICEP2 measurements of B-modes indicate a large tensor-to-scalar ratio in inflationary cosmology, which points towards trans-Planckian evolution of the inflaton. We propose possible string-theory realizations thereof. Schemes for natural and axion monodromy inflation are presented in the framework of the type IIB large volume scenario. The inflaton in both cases is given by the universal axion and its potential is generated at subleading order by F-terms. Our models are shown to feature a natural mechanism for inflaton decay into predominantly Standard Model particles.