Refined Study of Isocurvature Fluctuations in the Curvaton Scenario

TL;DR

This paper provides a detailed analysis of dark matter isocurvature perturbations in the curvaton model, revealing that previously underestimated effects can significantly suppress these perturbations, easing observational constraints.

Contribution

It introduces a refined analytical and numerical approach to evaluate isocurvature perturbations, accounting for curvaton decay effects often neglected in prior studies.

Findings

Isocurvature perturbations are significantly suppressed when dark matter freeze-out occurs deep in the curvaton-dominated era.

Current observational constraints on curvaton parameters are less restrictive than previously believed.

Decay of the curvaton can greatly influence the amplitude of isocurvature fluctuations.

Abstract

We revisit the generation of dark matter isocurvature perturbations in the curvaton model in greater detail, both analytically and numerically. As concrete examples, we investigate the cases of thermally decoupled dark matter and axionic dark matter. We show that the radiation produced by the decay of the curvaton, which has not been taken into account in previous analytical studies, can significantly affect the amplitude of isocurvature perturbations. In particular, we find that they are drastically suppressed even when the dark matter freeze-out (or the onset of the axion oscillations for axionic dark matter) occurs before the curvaton decays, provided the freeze-out takes place deep in the curvaton-dominated Universe. As a consequence, we show that the current observational isocurvature constraints on the curvaton parameters are not as severe as usually thought.