Question of Lorentz violation in muon decay

Possibilities to test the Lorentz invariance of the weak interaction in muon decay are considered. We derive the general Lorentz-violating muon-decay rate and discuss measurements of the directional and boost dependence of the Michel parameters and of the muon lifetime as function of absolute velocity. The current data on the muon lifetime at rest and in flight appear to be inconsistent. We make suggestions for dedicated reanalyses of the pertinent data and for future experiments. An interpretation in the Lorentz-violating Standard Model Extension is given.