Relativistic Freeze-in

Understand

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.