Constraints on variations in inflaton decay rate from modulated preheating

TL;DR

This paper investigates how modulated preheating can contribute to CMB perturbations, finding that its impact is limited to less than 15% of total perturbations unless parameters are finely tuned, especially if the modulating field is dark matter.

Contribution

It introduces constraints on the contribution of modulated preheating to CMB perturbations, considering the role of the modulating scalar as dark matter or not.

Findings

Modulated preheating can contribute up to 15% of CMB perturbations.

Fine tuning is required if the modulating scalar is dark matter.

Constraints on non-gaussianity and iso-curvature perturbations are established.

Abstract

Modulated (p)reheating is thought to be an alternative mechanism for producing super-horizon curvature perturbations in CMB. But large non-gaussianity and iso-curvature perturbations produced by this mechanism rule out its acceptability as the sole process responsible for generating CMB perturbations. We explore the situation where CMB perturbations are mostly generated by usual quantum fluctuations of inflaton during inflation, but a modulated coupling constant between inflaton and a secondary scalar affects the preheating process and produces some extra curvature perturbations. If the modulating scalar field is considered to be a dark matter candidate, coupling constant between the fields has to be unnaturally fine tuned in order to keep the local-form non-gaussianity and the amplitude of iso-curvature perturbations within observational limit; otherwise parameters of the models have to be tightly constrained. Those constraints imply that the curvature perturbations generated by modulated preheating should be less than 15% of the total observed CMB perturbations. On the other hand if the modulating scalar field is not a dark matter candidate, parameters of the models could not be constrained, but the constraints on the maximum amount of the curvature perturbations coming from modulated preheating remain valid.