Delta-N Formalism for Curvaton with Modulated Decay

TL;DR

This paper introduces a direct application of the δN-formalism to study curvature perturbations from modulated curvaton decay, providing a clearer and more unified approach compared to previous non-linear methods.

Contribution

The paper presents a novel direct δN-formalism approach for analyzing modulated curvaton decay, including cases with modulated mass and decay rate, unifying different modulation scenarios.

Findings

Method reproduces previous results on curvaton modulation.

Extends analysis to cases with modulated mass and decay rate.

Applicable to freezeout models with heavy species.

Abstract

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.