Non-gaussianity in axion Nflation models

TL;DR

This paper investigates non-gaussianity in multi-field axion Nflation models with a full cosine potential, revealing significant non-gaussian signals that could be detectable and differ from previous quadratic approximations.

Contribution

It provides a detailed analysis of perturbations in axion Nflation models using the full potential, showing larger non-gaussianity than previously estimated.

Findings

Tensor-to-scalar ratio and spectral index decrease but fit observations

Non-gaussianity parameter f_NL can be large and detectable

Non-gaussianity is a generic feature in multi-field hilltop inflation models

Abstract

We study perturbations in the multi-field axion Nflation model, taking account of the full cosine potential. We find significant differences with previous analyses which made a quadratic approximation to the potential. The tensor-to-scalar ratio and the scalar spectral index move to lower values, which nevertheless provide an acceptable fit to observation. Most significantly, we find that the bispectrum non-gaussianity parameter f_NL may be large, typically of order 10 for moderate values of the axion decay constant, increasing to of order 100 for decay constants slightly smaller than the Planck scale. Such a non-gaussian fraction is detectable. We argue that this property is generic in multi-field models of hilltop inflation.