Gravity Waves and Linear Inflation from Axion Monodromy
Liam McAllister, Eva Silverstein, Alexander Westphal
TL;DR
This paper presents a string-theoretic mechanism for large-field inflation via axion monodromy induced by space-filling wrapped branes. It analyzes how the resulting linear inflaton potential can be realized in warped Calabi–Yau and perturbative Ricci-curved compactifications while maintaining moduli stabilization, controlling flux and instanton corrections, and avoiding backreaction and η-problems. The authors provide concrete model realizations and toy examples, showing that a linear potential yields a detectable gravity-wave signal with $r\approx 0.07$ and $n_s\approx 0.975$, and discuss possible modulated signatures. The work highlights the generality and robustness of monodromy as a mechanism for large-field inflation in string theory and outlines directions for future model-building and observational tests.
Abstract
Wrapped branes in string compactifications introduce a monodromy that extends the field range of individual closed-string axions to beyond the Planck scale. Furthermore, approximate shift symmetries of the system naturally control corrections to the axion potential. This suggests a general mechanism for chaotic inflation driven by monodromy-extended closed-string axions. We systematically analyze this possibility and show that the mechanism is compatible with moduli stabilization and can be realized in many types of compactifications, including warped Calabi-Yau manifolds and more general Ricci-curved spaces. In this broad class of models, the potential is linear in the canonical inflaton field, predicting a tensor to scalar ratio r=0.07 accessible to upcoming cosmic microwave background (CMB) observations.