  The flavor of cosmic neutrinos may help unveil their sources and could reveal
the presence of new physics in the neutrino sector. We consider the impacts of
next-generation neutrino detectors, including the planned upgrade to neutrino
detector--IceCube-Gen2, which is well-positioned to make dramatic improvements
in both flavor and spectral measurements. We show that various models in
neutrino physics beyond the Standard Model, such as neutrino decay,
pseudo-Dirac states, and neutrino self-scattering, may be found or strongly
constrained at IceCube-Gen2 and KM3NeT. We find that the additional flavor
discriminants given by Glashow resonance events and so-called "double-bang"
topologies improve the ability to access the flavor of the cosmic high-energy
neutrinos and probe the BSM physics. In addition, although the details depend
on source properties, Glashow resonance events have the additional feature of
being able to inform us of the relative strengths of neutrino and antineutrino
emission, which may help us discriminate astrophysical scenarios.
