Reheating and Dark Matter Freeze-in in the Higgs-$R^2$ Inflation Model

TL;DR

This paper investigates the reheating process and freeze-in dark matter production in the Higgs-$R^2$ inflation model, highlighting the dominant thermal scattering mechanism and the resulting viable dark matter mass range.

Contribution

It provides a detailed analysis of the reheating temperature evolution and dark matter production mechanisms in the Higgs-$R^2$ inflation framework, including new insights into the dominant thermal freeze-in process.

Findings

Reheating temperature can reach up to $10^{14}$ GeV.

Dark matter with masses up to $10^9$ GeV can be produced.

Thermal scattering dominates dark matter production in this model.

Abstract

We study the post-inflationary dynamics for reheating and freeze-in dark matter in the Higgs-$R^2$ inflation model. Taking the perturbative approach for reheating, we determine the evolution of the temperature for radiation bath produced during reheating and determine the maximum and reheating temperatures of the Universe. Adopting a singlet scalar dark matter with a conformal non-minimal coupling and a vanishing Higgs-portal coupling, we discuss the freeze-in production of dark matter both from the non-thermal scattering during reheating and the thermal scattering after reheating. We find that thermal scattering is dominant for dark matter production in our model due to the high reheating temperature. The reheating temperature in our model is determined dominantly by the Higgs condensate to be up to about $10^{14}\,{\rm GeV}$ and dark matter with masses up to about $10^9\,{\rm GeV}$ can be produced with a correct relic density.