Stepping into the Forest: Confronting Interacting Radiation Models for the Hubble Tension with Lyman-$\alpha$ Data

Understand

Models of interacting dark radiation have been shown to alleviate the Hubble tension.

• Extensions incorporating a coupling between dark matter and dark radiation (DM-DR) have been proposed as combined solutions to both the Hubble and $S_8$ tensions.
• A key feature of these extended models is a break in the matter power spectrum (MPS), suppressing power for modes that enter the horizon before the DM-DR interactions turn off.
• In scenarios with a massless mediator, modes that enter before matter-radiation equality get suppressed, whereas for massive mediators, the break is determined by the mediator mass, a free parameter.