Heavy neutrino searches through double-bang events at Super-Kamiokande, DUNE, and Hyper-Kamiokande

A variety of new physics scenarios allow for neutrinos to up-scatter into a heavy neutral lepton state. For range couplings and neutrino energies, the may travel some distance before decaying visible final states. When both up-scattering decay occur within detector volume, these "double bang" events produce distinctive phenomenology with very low background. In this work, we first consider current sensitivity at Super-Kamiokande via atmospheric flux, find data already provide constraints. We then examine projected future DUNE Hyper-Kamiokande, including beam flux contributions double-bang signals.