Revisiting freeze-in dark matter from renormalizable operators

TL;DR

This paper investigates the production of feebly interacting dark matter particles during the ultra-relativistic regime, emphasizing the importance of high-temperature processes previously overlooked in models with renormalizable operators.

Contribution

It provides a detailed analysis of dark matter production at high temperatures, highlighting the significance of soft scatterings and $2 o 2$ processes in the early universe.

Findings

High-temperature regime significantly affects dark matter abundance.

Soft scatterings contribute substantially to particle production.

Neglecting the ultra-relativistic regime can underestimate dark matter density.

Abstract

In this conference paper we summarise the findings of a recent study, where the impact of the ultra-relativistic regime on the production of a feebly interacting dark matter particle is considered. As its population accumulates over the thermal history, we inspected thoroughly the temperature window $T \gg M$, which has been previously neglected in the context of dark matter models with renormalizable operators. At high temperatures, and for the model considered in our work, the production rate of the feebly interacting particle is driven by multiple soft scatterings, as well as $2 \to 2$ processes, that can give a large contribution to the dark matter energy density.