Curvaton scenarios with inflaton decays into curvatons

TL;DR

This paper investigates how inflaton decay into curvatons during reheating affects cosmological predictions, finding that such decays mainly alter the background evolution without observable signatures, constraining decay rates.

Contribution

It provides a detailed analysis of inflaton decay into curvatons, showing the impact on background evolution and setting bounds on decay branching ratios.

Findings

Decay curvatons change the Universe's background history.

No observable signatures beyond background modifications.

Branching ratio constraints prevent curvaton domination.

Abstract

We consider the possible decay of the inflaton into curvaton particles during reheating and analyse its effect on curvaton scenarios. Typical decay curvatons are initially relativistic then become non-relativistic, changing the background history of the Universe. We show that this change to the background is the only way in which observational predictions of the scenario are modified. Moreover, once the required amplitude of perturbations is fixed by observation there are no signatures of such decays in other cosmological observables. The decay curvatons can prevent the Universe from becoming dominated by the curvaton condensate, making it impossible to match observations in parts of parameter space. This constrains the branching ratio of the inflaton to curvaton to be less than of order $0.1$ typically. If the branching ratio is below about $10^{-4}$ it has negligible impact on the model parameter space and can be ignored.