Astrophysical neutrinos: Flavor ratios depend on energy

Electromagnetic (and adiabatic) energy losses of pi's and mu's modify the flavor ratio (measured at Earth) of neutrinos produced by pi decay in astrophysical sources, Phi(nu e)Phi(nu mu)Phi(nu tau), from 1:1:1 at low energy to 1:1.8:1.8 at high energy. The transition occurs over 1-2 decades of nu energy, and is correlated with a modification of the neutrino spectrum. For gamma-ray bursts, e.g., the transition is expected at similar to 100 TeV and may be detected by km-scale nu telescopes. Measurements of the transition energy and energy width will provide unique probes of the physics of the sources. pi and mu energy losses also affect the ratio of (nu) over bar (e) flux to total nu flux, which may be measured at the W resonance (6.3 PeV): It is modified from 1/6 (1/15) at low energy to 1/9 (practically 0) at high energy for neutrinos produced in pp (p gamma) interactions.