Intrinsic flavor violation in neutrinos produced through decays

Abstract

We show there is a non-null probability to produce neutrinos of the ``wrong'' type in general decays, within the SM augmented by the known three massive neutrinos and nontrivial mixing. Such effect is equivalent to an intrinsic flavor violation (lepton flavor violation) at creation without requiring neutrino propagation. The exact amount of flavor violation depends on the neutrino flavor state to be detected. For realistic conditions, the violation is tiny but much larger than other indirect lepton flavor violation processes not involving neutrinos as final states. For neutrinos produced in a continuous spectrum, we show the effect is larger, in relative terms, for neutrinos produced in the low-energy portion of the spectrum. For muon decay, if the usual neutrino flavor state is assumed a flavor violation as large as 1\% is possible in the channel $\mu^+\to\bnu_\tau e^+ \nu_e$. We also discuss the relation between flavor violation and flavor indefiniteness for neutrino flavor states.