Non-gaussianity in axion N-flation models: detailed predictions and mass spectra

TL;DR

This paper analyzes multi-field axion N-flation models, predicting observable non-gaussianity and detailed spectral features, with a focus on mass spectra and their implications for cosmological observations.

Contribution

It extends previous work by analyzing equal and unequal mass axions, providing probability distributions and correlations of observables, and outlining specific testable predictions.

Findings

Mass spectrum must be densely packed for observational consistency

Model predicts specific values for spectral index, tensor-to-scalar ratio, bispectrum, and trispectrum

Unequal masses require fine-tuning to match observations

Abstract

We have recently shown that multi-field axion N-flation can lead to observable non-gaussianity in much of its parameter range, with the assisted inflation mechanism ensuring that the density perturbations are sufficiently close to scale invariance. In this paper we extend our analysis in several directions. In the case of equal-mass axions, we compute the probability distributions of observables and their correlations across the parameter space. We examine the case of unequal masses, and show that the mass spectrum must be very densely packed if the model is to remain in agreement with observations. The model makes specific testable predictions for all major perturbative observables, namely the spectral index, tensor-to-scalar ratio, bispectrum, and trispectrum.