# Relativistic Freeze-in

## TL;DR

This paper investigates the production of scalar dark matter through the relativistic freeze-in process in the Higgs portal model, accounting for thermal effects and phase transition impacts to derive relevant constraints.

## Contribution

It provides the first detailed derivation of relativistic reaction rates for scalar dark matter production, including thermal mass effects and electroweak phase transition considerations.

## Key findings

- Derived relativistic reaction rates with Bose-Einstein statistics
- Established constraints on Higgs portal coupling
- Analyzed thermal mass effects and phase transition impacts

## Abstract

We study production of scalar dark matter via the freeze--in mechanism in the relativistic regime, focussing on the simplest Higgs portal model. We derive the corresponding relativistic reaction rates based on the Bose--Einstein statistics taking into account the thermal mass effects as well as the change in the Higgs degrees of freedom at the electroweak phase transition. The consequent constraints on the Higgs portal coupling are obtained.