Investigating sub-MeV dark matter annihilation to neutrinos using direct detection experiments

Dark matter (DM) could self-annihilate into neutrinos in dense regions of the Universe. We consider the resulting flux of neutrinos from the Milky Way DM halo and derive exclusion limits on the annihilation cross-section using XENONnT electron recoil data. Assuming a $J$-factor independent of the annihilation cross-section, we find leading limits for DM masses below $\mathcal{O}$(MeV). Self-annihilating DM affects the DM halo via dissolution, introducing a cross-section dependency on the halo profile and thus the $J$-factor. We discuss such a situation in more detail, finding that the signal rate is below the experimental sensitivity of XENONnT, leaving the annihilation cross-section unconstrained.