Speaker
Description
We present the differential decay rates and the branching ratios of the tau and muon decays with internal conversion, τ→ℓℓ′ℓ′νν¯ and μ→eeeνν¯, in the Standard Model at NLO in the on-shell scheme.
These five-body leptonic decays are a tool to study the Lorentz structure of the weak interactions and to test lepton flavor universality. They are also a source of SM background for charged-lepton-flavor-violation searches of the forbidden decays μ→eee and τ→ℓℓ′ℓ′.
Even if the shift in the branching ratios induced by radiative corrections turns out to be small and of order 1% --- mainly due to a running effect of the fine-structure constant α --- locally in the phase space these corrections can reach the 5-10 % level, depending on the applied cuts.
We found for instance that in the phase space region where the neutrino energies are small, and the momenta of the three charged leptons have a similar signature as in the μ→eee and τ→ℓℓ′ℓ′ decays, the NLO corrections decrease the leading-order prediction by about 10-20 %.
