The Milky Way is a Laboratory for New Ultra-long-baseline Neutrino Physics

The IceCube Neutrino Observatory recently published evidence for diffuse neutrino emission from the Galactic Plane at 4.5σ significance. This new source of astrophysical neutrinos provides an exciting laboratory for probing the nature of neutrino masses. In particular, extremely small mass splittings, such as those predicted by quasi-Dirac neutrino mass models, and finite neutrino lifetimes from neutrino decays, would induce effects on the spectra and flavor ratios of neutrinos with TeV-scale energies traversing kiloparsec-scale baselines. Using TANDEM, an upcoming three dimensional galactic neutrino emission model, we explore the sensitivity of IceCube and KM3NeT/ARCA to these ultra-long-baseline phenomena. We find that a combined analysis would be sensitive to quasi-Dirac mass splittings 10-14.0~eV² δ m² 1011.6~eV² and neutrino lifetimes m / τ 10-14.1~eV² at > 1σ, both regions constituting as-yet unexplored parameter space. Our results demonstrate the potential that astrophysical neutrino sources and global neutrino telescope networks have in probing new regions of exotic neutrino mass models.