Constraining dark matter-neutrino interactions using the CMB and large-scale structure

We present a new study on the elastic scattering cross section of dark matter (DM) and neutrinos using the latest cosmological data from Planck and large-scale structure experiments. We find that the strongest constraints are set by the Lyman-α forest, giving σ DM−ν ≲ 10 −33 ( m DM /GeV) cm 2 if the cross section is constant and a present-day value of σ DM−ν ≲ 10 −45 ( m DM /GeV) cm 2 if it scales as the temperature squared. These are the most robust limits on DM-neutrino interactions to date, demonstrating that one can use the distribution of matter in the Universe to probe dark (``invisible") interactions. Additionally, we show that scenarios involving thermal MeV DM and a constant elastic scattering cross section naturally predict (i) a cut-off in the matter power spectrum at the Lyman-α scale, (ii) N eff ∼ 3.5 ± 0.4, (iii) H 0 ∼ 71 ± 3km s −1 Mpc −1 and (iv) the possible generation of neutrino masses.