Non-Gaussianity from Axionic Curvaton

Understand

We study non-Gaussianity of density perturbations generated by an axionic curvaton, focusing on the case that the curvaton sits near the hilltop of the potential during inflation.

• Such hilltop curvatons can generate a red-tilted density perturbation spectrum without invoking large-field inflation.
• We show that, even when the curvaton dominates the Universe, the non-Gaussianity parameter fNL is positive and mildly increases towards the hilltop of the curvaton potential, and that fNL = O(10) is a general and robust prediction of such hilltop axionic curvatons.
• In particular, we find that the non-Gaussianity parameter is bounded as fNL <~ 30 - 40 for a range of the scalar spectral index, ns = 0.94 - 0.99, and that fNL = 20 - 40 is realized for the curvaton mass m_\sigma = 10 - 10^6 GeV and the decay constant f = 10^{12} - 10^{17} GeV.