Decay of High-Energy Astrophysical Neutrinos

Existing limits on the nonradiative decay of one neutrino to another plus a massless particle (e.g., a singlet Majoron) are very weak. The best limits on the lifetime to mass ratio come from solar neutrino observations and are τ/m10^-4 s/eV for the relevant mass eigenstate(s). For lifetimes even several orders of magnitude longer, high-energy neutrinos from distant astrophysical sources would decay. This would strongly alter the flavor ratios from the ${{φ}}_{{{ν}}ₑ}{:}{{φ}}_{{{ν}}_{{μ}}}{:}{{φ}}_{{{ν}}_{{τ}}}=1{:}1{:}1$ expected from oscillations alone and should be readily visible in the near future in detectors such as IceCube.