Speaker
Description
Models of a dark radiation sector with a mass threshold have been shown to ease the two currently outstanding cosmological tensions. In particular, addition of radiation in the early universe can naturally raise $H_0$ by widening the sound horizon at recombination. An additional coupling between the radiation and dark matter at early times induces dark matter scattering at small scales, which helps to lower the clustering amplitude $S_8$. Recently, lensing measurements from data release 6 by the ACT collaboration have provided strong preference within $\Lambda$CDM for a higher value of $S_8$. In this work, we explore the implications of recent CMB measurements from Planck, ACT and SPT for $S_8$ within a model with dark radiation scattering. We find within this model, the data prefer an $S_8$ value near the late universe measurements without the need to implement $S_8$ priors from DES-Y3 and KiDS-1000 measurements. However, we find this comes at a deficit to the model's ability to simultaneously ease the Hubble tension. We comment on future improvements expected from upcoming data releases.
