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We investigate non-Gaussianity in the modulated reheating scenario wherefluctuations of the decay rate of the inflaton generate adiabaticperturbations, paying particular attention to the non-linearity parameters$f_{\rm NL}, \tau_{\rm NL}$ and $g_{\rm NL}$ as well as the scalar spectralindex and tensor-to-scalar ratio which characterize the nature of theprimordial power spectrum. We also take into account the pre-existing adiabaticperturbations produced from the inflaton fluctuations. It has been known thatthe non-linearity between the curvature perturbations and the fluctuations ofthe decay rate can yield non-Gaussianity at the level of $f_{\rm NL} \sim\mathcal{O}(1)$, but we find that the non-linearity between the decay rate andthe modulus field which determines the decay rate can generate much greaternon-Gaussianity. We also discuss a consistency relation among non-linearityparameters which holds in the scenario and find that the modulated reheatingyields a different one from that of the curvaton model. In particular, theyboth can yield a large positive $f_{\rm NL}$ but with a different sign of$g_{\rm NL}$. This provides a possibility to discriminate these two competitivemodels by looking at the sign of $g_{\rm NL}$. Furthermore, we work on someconcrete inflation models and investigate in what cases models predict thespectral index and the tensor-to-scalar ratio allowed by the current data whilegenerating large non-Gaussianity, which may have many implications formodel-buildings of the inflationary universe.

Primordial Curvature Fluctuation and Its Non-Gaussianity in Models with Modulated Reheating