Luminous solar neutrinos. II. Mass-mixing portals.

Solar neutrinos can be efficiently upscattered to MeV-scale heavy neutral leptons (HNLs) within the Earth's mantle. HNLs can then decay to electron-positron pairs leading to energy deposition inside large volume detectors. In this paper, we consider mass-portal upscattering of solar neutrinos to HNLs of mass 20 MeV≥mN≥2me. The large volume of the Earth compensates for the long decay length of the HNLs leading to observable rates of N→ναe+e- in large volume detectors. We find that searches for mantle-upscattered HNLs can set novel limits on mixing with third-generation leptons, |UτN| for masses in the MeV regime; sensitivity to mixing with first- and second-generation leptons is not competitive with existing search strategies. [ABSTRACT FROM AUTHOR]