Probing BSM Physics with Neutrinos from Astrophysical Sources at IceCube

The recent observation of NGC 1068 by the IceCube Neutrino Observatory has opened a new window to neutrino physics at astrophysical scales. In this Letter, we propose a new method to probe the nature of neutrino masses using these observations. In particular, our method enables searching for signatures of pseudo-Dirac neutrinos with mass-squared differences that reach down to δm^{2 ≥} 10−21 eV², improving the reach of terrestrial experiments by more than a billion. Finally, we discuss how the discovery of a constellation of neutrino sources can further increase the sensitivity and cover a wider range of δm² values.