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Decay of High-Energy Astrophysical Neutrinos

Existing limits on the non-radiative 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 $τ/m \agt 10^{-4}$ 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.