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fzero
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arivero said:I am not sure. Consider a decay muon to electron plus a pair neutrino antineutrinos, as usual. As it is possible that the electron is left in the same rest frame that the initial muon, I could say that the energy available for the neutrino pair is the difference of pole masses of muon and electron, not the muon pole mass minus the renormalised electron mass at muon scale. I think I should had put more care when I attended to the undergraduate lectures, twenty years ago.
Of course it is irrelevant for the experimental results, the running of electron fro .511 to 105 is surely negligible.
Thinking a bit more, I think the best way to look at the issue is the most straightforward. If you compute the decay using the bare masses, then a proper treatment of loop corrections automatically takes into account running of the masses and coupling constants. Determining what bare parameters to use amounts to choosing a renormalization scheme and then extracting the pole mass by finding the pole in the full propagator.
I think that any simplification (like just using effective mass parameters) probably leaves too much physics out that is of the same degree of importance.