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 ν = 22 0 − 110 + 570 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 σ DM − ν / m DM ≲ 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 ∼ 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. We find that the constraints from the KM3-230213A high-energy event for these simplified models are almost entirely ruled out for masses above the mega-electron-volts by unitarity constraints. Therefore, the attenuation of such energetic neutrinos by dark matter calls for richer dark sectors in order to produce meaningful constraints.