Axion Inflation in F-theory
Thomas W. Grimm
TL;DR
The paper proposes axion-like inflatons arising from harmonic three-forms on elliptically fibered Calabi-Yau fourfolds in F-theory, whose decay constants depend on complex-structure moduli that can be fixed by fluxes. Localization of axions near strong-coupling regions on the base seven-branes can enhance the decay constants, potentially achieving super-Planckian values in a controlled setting. Embedding natural inflation into four-dimensional N=1 supergravity, the authors show how a non-perturbative superpotential yields an axion potential with suppressed higher harmonics, enabling large r for suitable parameter choices. They highlight the need for explicit Calabi-Yau fourfold examples and careful moduli stabilization to realize these models in practice, while leaving reheating and detailed phenomenology for future work.
Abstract
We study the dynamics of axion-like fields in F-theory and suggest that they can serve as inflatons in models of natural inflation. The axions arise from harmonic three-forms on the F-theory compactification space and parameterize a complex torus that varies over the geometric moduli space. In particular, this implies that the axion decay constants depend on the complex structure moduli that can be fixed by background fluxes. This might allow tuning them to be super-Planckian in a controlled way and allow for interesting single field inflationary models. We argue that this requires a localization of the three-forms near regions of strong string coupling, analogously to the reasoning that GUT physics requires the use of F-theory. These models can admit a tensor to scalar ratio r>0.1.