Abstract: Models of interacting dark radiation have been proposed to alleviate the Hubble tension. Extensions that couple dark matter and dark radiation (DM-DR) offer potential solutions to both the Hubble and Large-Scale Structure (LSS) tensions. To address LSS tensions, these models introduce a break in the matter power spectrum (MPS), suppressing power for modes entering the horizon before DM-DR interactions turn off. Resolving the Hubble tension requires dark radiation to emerge just before matter-radiation equality (MRE) and dilute afterward.
In this talk, I introduce a few proposed models – including a model based on evaporation of axion DM into dark photons – and evaluate them against LSSprobes: weak lensing, CMB lensing, full-shape galaxy clustering, and eBOSS measurements of the 1D Lyman-a forest flux power spectrum, as well as Hubble constant measurements from the SH0ES collaboration. The Lyman-a data are particularly constraining due totheir sensitivity to small scales where many models predict significant deviations. Indeed, eBOSS Lyman-a data already show tension with Planck CMB data in CDM, with Lyman-a favoring a steeper MPS slope at smaller scales.
We find that while simple dark radiation models improve the Hubble tension, they worsen the fit to Lyman-a data. However, models with DM-DR interactions show promise in addressing both tensions simultaneously.