SN1987A still shining: A Quest for Pseudo-Dirac Neutrinos

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 ($\Delta\chi^2\approx 3$)for$\delta m^2=6.31\times 10^{-20}{\rm eV}^2$. Notably, the same data is able to exclude $\delta m^2\sim [2.55,3.01]\times {10}^{-20}{\mathrm{e}\mathrm{V}}^2$ with $\mathrm{\Delta }{\chi }^2>9$, 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.