The Highest-Energy Neutrino Event Constrains Dark Matter-Neutrino Interactions

Dark Matter-neutrino interactions affect the propagation of astrophysical neutrinos, attenuating the flux of neutrinos arriving at Earth. Using the highest-energy neutrino event detected to date by the KM3NeT collaboration as an example, and assuming an extragalactic origin, we derive limits on these interactions at $E_\nu = 220^{+570}_{-110}\, \mathrm{PeV}$. Considering only the propagation on the Milky Way Dark Matter halo, we constrain the interaction cross section over the mass of the Dark Matter candidate to be, $\sigma_{\rm DM-\nu}/m_{\rm DM} \lesssim 10^{-22}$~cm$^2$~GeV$^{-1}$. If a transient source was positively identified, the high-energy neutrino would have crossed the dark-matter halo of the source host as well, resulting in more stringent constraints (e.g., up to $ \sim$ 6 orders of magnitude assuming the blazar PKS 0605-085 is the source). These bounds on the Dark Matter-neutrino interaction cross section are translated into limits on the mass of the Dark Matter candidate, the mass of the mediator, and the coupling strength for different simplified models. In particular, we find that the KM3-230213A high-energy event sets the most stringent constraints on models where the scattering cross section rises in the high-energy limit. We identify vector Dark Matter interacting with neutrinos via vector mediators as the most promising scenario, and show that high-energy neutrinos provide world-leading limits in this model, testing the region of parameter space motivated by thermal freeze-out.