The weak, the strong and the ugly -- A comparative analysis of interacting stepped dark radiation

Understand

Models which address both the Hubble and $S_8$ tensions with the same mechanism generically cause a pre-recombination suppression of the small scale matter power spectrum.

• Here we focus on two such models.
• Both models introduce a self-interacting dark radiation fluid scattering with dark matter, which has a step in its abundance around some transition redshift.
• In one model, the interaction is weak and with all of the dark matter whereas in the other it is strong but with only a fraction of the dark matter.