Towards Natural Inflation in String Theory

TL;DR

The paper addresses how to realize large-field natural inflation within a string-theoretic framework by embedding two-axion models (KNP alignment and Hierarchical Axions) into type IIB compactifications with RR C2 axions. It develops explicit supergravity and string-compactification realizations, showing how moduli stabilization via KKLT and LVS can be arranged so that the inflationary sector decouples from heavy moduli and yields an effectively trans-Planckian decay constant f_eff without uncontrolled backreaction. It provides both KKLT and LVS realizations, analyzes the necessary hierarchies and misalignment parameters, and presents concrete examples with D5 and ED3/ED1 non-perturbative effects to generate the axion potential. The work demonstrates that natural inflation can be UV-completed in string theory with a minimal axion content, non-perturbative dynamics, and controlled stability, offering a concrete path toward observationally viable large-field inflation in a quantum-gravity framework.

Abstract

We provide type IIB string embeddings of two axion variants of natural inflation. We use a combination of RR 2 form axions as the inflaton field and have its potential generated by non perturbative effects in the superpotential. Besides giving rise to inflation, the models developed take into account the stabilization of the compact space, both in the KKLT and large volume scenario regimes, an essential condition for any semi-realistic model of string inflation.

Figures (1)

• Figure 1: Scalar potential in the $(b_1,b_2)$ plane for $\{A,B, W_0, r, \delta, b_1, a_1\}=\{ 0.002, 0.001, 1, 2, 0.1, 0.1, 0.05\}$. Right: $V_0$, left: $V_1$. Note the hierarchy between the two contributions to $V$.