Curvaton as dark matter with secondary inflation

TL;DR

This paper proposes a cosmological model where a long-lived curvaton acts as dark matter, influenced by a secondary inflation, leading to specific perturbation signatures and potential QCD axion identification.

Contribution

It introduces a scenario where a curvaton serves as dark matter affected by secondary inflation, predicting unique non-Gaussianity parameters and suppressing isocurvature perturbations.

Findings

Curvaton can be dark matter with suppressed isocurvature perturbations.

Secondary inflation dilutes curvaton abundance, avoiding decay into Standard Model particles.

Predicted non-Gaussianity parameters are fNL ~ 1.25 and gNL ~ 0.

Abstract

We consider a novel cosmological scenario in which a curvaton is long-lived and plays the role of cold dark matter (CDM) in the presence of a short, secondary inflation. Non-trivial evolution of the large scale cosmological perturbation in the curvaton scenario can affect the duration of the short term inflation, resulting in the inhomogeneous end of inflation. Non-linear parameters of the curvature perturbation are predicted to be fNL ~ 5/4 and gNL ~ 0. The curvaton abundance can be well diluted by the short-term inflation and accordingly, it does not have to decay into the Standard Model particles. Then the curvaton can account for the present CDM with the isocurvature perturbation being sufficiently suppressed because both the adiabatic and CDM isocurvature perturbations have the same origin. As an explicit example, we consider the thermal inflation scenario and a string axion as a candidate for this curvaton-dark matter. We further discuss possibilities to identify the curvaton-dark matter with the QCD axion.