First numerical study of Neutrino-Dark Matter Mixed Damping

Mixed Damping is a physical effect that occurs when two fluids have interactions with each other but the particles in one fluid are already free-steaming. As such, it is a cross between collisional damping and free-streaming and has never been studied numerically. Mixed damping is particularly relevant in the context of dark matter-neutrino weak interactions and therefore should not be neglected. Here, we provide an accurate, self-consistent, description of the dark matter-neutrino interactions, which accounts for the different damping regimes. This work is critical to characterise the dark matter microphysics and will be extremely important if measurements of the matter power spectrum at small-scales indicate a departure from the $\Lambda$CDM predictions.