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 $\tau/m \agt 10^{ -4}$ 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 $\phi_{ \nu_e}:\phi_{ \nu_{ \mu}}:\phi_{ \nu_{ \tau}} = 1:1:1$ expected from oscillations alone, and should be readily visible in the near future in detectors such as IceCube.
Categories: hep-ph astro-ph