Signs of pseudo-Dirac neutrinos in SN1987A data

Ever since the discovery of neutrinos, we have wondered if neutrinos are their own antiparticles. One remarkable possibility is that neutrinos have a pseudo-Dirac nature, predicting a tiny mass difference between active and sterile states. We analyze the neutrino data from SN1987A in the light of active-sterile oscillations and find a mild preference (Δχ²≈3) for δm²=6.31×10^-20 eV². Notably, the same data is able to exclude δm²~[2.55,3.01]×10^-20 eV² with Δχ²>9, the tiniest mass differences constrained so far. We further consider the next-generation of experiments and demonstrate their sensitivity exploring the nature of the neutrino mass.