Dark Matter Freeze-In with a Heavy Mediator: Beyond the EFT Approach

Understand

We study dark matter freeze-in scenarios where the mass of the mediator particle that couples dark matter to the Standard Model is larger than the reheat temperature, TRH, in the early Universe.

• In such setups, the standard approach is to work with an effective field theory (EFT) where the mediator is integrated out.
• We examine the validity of this approach in various generic s- and t-channel mediator frameworks.
• We find that the EFT approach breaks down when the mediator mass is between one to two orders of magnitude larger than TRH due to various effects such as s-channel resonance, a small thermally-suppressed abundance of the mediator, or decays of Standard Model particles through loops induced by the mediator.