Non-Gaussianity in axion N-flation models: Detailed predictions and mass spectra

We have recently shown [ S. A. Kim, A. R. Liddle and D. Seery Phys. Rev. Lett. 105 181302 (2010)] that multifield 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.