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In light of the recent kurfuffle of FTL neutrinos I wonder, do neutrinos 'become' other particles between their oscillations between the different flavors of neutrino? I'm slightly familiar with Feynman diagrams and wonder if there's some state between, say, electron and muon neutrino that may account for a neutrino's apparent FTL properties over a short distance, but would be averaged away over longer distances.

In short is the transition from electron -> muon -> tau neutrino more like electron neutrino -> (tachyon) -> muon neutrino -> (slower particle) -> tau neutrino?

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Side note: oscillation does not imply a well defined sequence of flavors as you write above. The proper way to think of this is $\nu_\text{created flavor} \to \text{time dependent linear combination of } \nu_1, \nu_2, \nu_3 \to \nu_\text{detected flavor}$ where the $\nu_i$'s are the mass states. –  dmckee Oct 1 '11 at 16:52
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Neutrino oscillations work by a mismatch between the mass eigenstates and the eigenstates of weak interactions. This lepton mixing is the same type of mixing described by the CKM matrix for quarks.

The quick answer to your question would be, that in order to oscillate into other types of particles while staying in the framework currently used to describe neutrino oscilations there would need to be more families of leptons (and quarks), than the three observed. The number of light neutrinos has been fairly well measured to be three by the LEP experiment. Any fourth generation neutrino must be heavier than half the Z mass.

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