Extended Analysis of Neutrino-Dark Matter Interactions with Small-Scale CMB Experiments

We explore an extension of the standard $\mathrm{\Lambda }$CDM model by including an interaction between neutrinos and dark matter, and making use of the ground based telescope data of the Cosmic Microwave Background (CMB) from the Atacama Cosmology Telescope (ACT). An indication for a non-zero coupling between dark matter and neutrinos (both assuming a temperature independent and $T^2$ dependent cross-section) is obtained at the 1$\sigma$ level coming from the ACT CMB data alone and when combined with the Planck CMB and Baryon Acoustic Oscillations (BAO) measurements. This result is confirmed by both fixing the effective number of relativistic degrees of freedom in the early Universe to the Standard Model value of $N_{\mathrm{e}\mathrm{f}\mathrm{f}}=3.044$, and allowing $N_{\mathrm{e}\mathrm{f}\mathrm{f}}$ to be a free cosmological parameter. Furthermore, when performing a Bayesian model comparison, the interacting $\nu$DM (+$N_{\mathrm{e}\mathrm{f}\mathrm{f}}$) scenario is mostly preferred over a baseline $\mathrm{\Lambda }$CDM (+$N_{\mathrm{e}\mathrm{f}\mathrm{f}}$) cosmology. The preferred value is then used as a benchmark and the potential implications of dark matter’s interaction with a sterile neutrino are discussed.