Inflationary NonGaussianity from Thermal Fluctuations

Abstract

We calculate the contribution of the fluctuations with the thermal origin to the inflationary nonGaussianity. We find that even a small component of radiation can lead to a large nonGaussianity. We show that this thermal nonGaussianity always has positive $f_{\mathrm{NL}}$. We illustrate our result in the chain inflation model and the very weakly dissipative warm inflation model. We show that $f_{NL}\sim \mathcal{O}(1)$ is general in such models. If we allow modified equation of state, or some decoupling effects, the large thermal nonGaussianity of order $f_{\mathrm{NL}}>5$ or even $f_{\mathrm{NL}}\sim 100$ can be produced. We also show that the power spectrum of chain inflation should have a thermal origin. In the Appendix A, we made a clarification on the different conventions used in the literature related to the calculation of $f_{\mathrm{NL}}$.

20 pages, 1 figure. v2, v3: references and acknowledgments updated

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