Converting dark matter to dark radiation does not solve cosmological tensions

Understand

Tensions between cosmological parameters (in particular the local expansion rate $H_0$ and the amplitude of matter clustering $S_8$) inferred from low-redshift data and data from the cosmic microwave background (CMB) and large-scale structure (LSS) experiments have inspired many extensions to the standard cosmological model, $\Lambda$CDM.

• Models which simultaneously lessen both tensions are of particular interest.
• We consider one scenario with the potential for such a resolution, in which some fraction of the dark matter has converted into dark radiation since the release of the CMB.
• Such a scenario encompasses and generalizes the more standard "decaying dark matter" model, allowing additional flexibility in the rate and time at which the dark matter converts into dark radiation.