Non-Gaussianity in the unified curvaton mechanism : The generalized curvaton mechanism that comprehends modulation at the transition

Generation of the curvature perturbation is calculated when the modulation is implemented in the generalized curvaton mechanism, in which the curvaton may not scale like matter. We first consider the slow-roll curvaton scenario with/without modulation at the end of the slow-roll, where the curvaton and the modulation share the same source of the perturbation. We calculate the non-linearity parameter using the non-linear formalism, which is the first exact analytical calculation of the non-Gaussianity created by the slow-roll curvaton. Unlike the conventional curvaton mechanism, in which $f_NL$ can become large but arbitrary, our result shows that $f_NL∼ O(10)$ could be natural in the typical inflating curvaton scenario. Our calculation is also valid in the conventional modulation that is usually caused by an extra light field, in which the curvaton and the modulation may have the individual (separable) source of the perturbations. For the separable perturbations we consider the simplest multi-field inflation.