Natural and Multi-Natural Inflation in Axion Landscape

TL;DR

This paper explores a landscape of many axions with varied potentials, showing that super-Planckian decay constants are common and can lead to natural or multi-natural inflation, addressing observational tensions.

Contribution

It demonstrates the frequent occurrence of super-Planckian axion decay constants in the landscape and links this to natural and multi-natural inflation models.

Findings

Super-Planckian axion decay constants are common in the landscape.

Inflation models can be natural or multi-natural depending on axion parameters.

The total inflation duration is around 60 e-folds for typical potential heights.

Abstract

We propose a landscape of many axions, where the axion potential receives various contributions from shift symmetry breaking effects. We show that the existence of the axion with a super-Planckian decay constant is very common in the axion landscape for a wide range of numbers of axions and shift symmetry breaking terms, because of the accidental alignment of axions. The effective inflation model is either natural or multi-natural inflation in the axion landscape, depending on the number of axions and the shift symmetry breaking terms. The tension between BICEP2 and Planck could be due to small modulations to the inflaton potential or steepening of the potential along the heavy axions after the tunneling. The total duration of the slow-roll inflation our universe experienced is not significantly larger than $60$ if the typical height of the axion potentials is of order $(10^{16-17}{\rm \,GeV})^4$.