New insights on ν–DM interactions

We revisit the possibility of using cosmological observations to constrain models that involve interactions between neutrinos and dark matter. We show that small-scale measurements of the cosmic microwave background (CMB) with a few per cent accuracy are critical to uncover unique signatures from models with tiny couplings that would require a much higher sensitivity at lower multipoles, such as those probed by the Planck satellite. We analyse the high-multipole data released by the Atacama Cosmology Telescope, both independently and in combination with Planck and baryon acoustic oscillation measurements, finding a compelling preference for a non-vanishing coupling, log10 uνDM = −5.20+1.2 −0.74 at 68 per cent confidence level. This aligns with other CMB-independent probes, such as Lyman-α. We illustrate how this coupling could be accounted for in the presence of dark matter interactions with a sterile neutrino.