Delta-N Formalism for Curvaton with Modulated Decay
  In this paper, the curvature perturbation generated by the modulated curvaton
decay is studied by a direct application of $\delta N$-formalism. Our method
has a sharp contrast with the {\it non-linear formalism} which may be regarded
as an indirect usage of $\delta N$-formalism. We first show that our method can
readily reproduce results in previous works of modulation of curvaton. Then we
move on to calculate the case where the curvaton mass (and hence also the decay
rate) is modulated. The method can be applied to the calculation of the
modulation in the freezeout model, in which the heavy species are considered
instead of the curvaton. Our method explains curvaton and various modulation on
an equal footing.
