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) cm² if the cross section is constant and a present-day value of σ_DM−ν ≲ 10⁻⁴⁵(m_DM/GeV) cm² 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) H₀ ∼ 71 ± 3km s⁻¹Mpc⁻¹ and (iv) the possible generation of neutrino masses.