Complete O(Nfα2) weak contributions to the muon lifetime Original Research Article

The complete O(Nfα2) weak contributions to the muon lifetime, denoted as Δr(2), are calculated in the MS renormalization scheme. These come from 2-loop Feynman diagrams containing a loop formed by complete generations of massless fermions. They form an independent, gauge-invariant set of corrections that, because of the large number of light fermions in the Standard Model, is expected to make a significant contribution. In the MS renormalizaton scheme with μ′ — (πeγ)12 μ = MZ and for a Higgs mass, MH, in the range 100–1000 GeV the contribution varies from −0.55 × 10−4 to −1.54 × 10−4 for each massless generation of fermions.