Complete O(Nα2) weak contributions to the muon lifetime

Abstract

The complete O(N f α 2 ) weak contributions to the muon lifetime, denoted as ∆r (2) , are calculated in the MS renormalization scheme. These come from 2loop 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 renormalization scheme with µ ′ ≡ (πe γ ) 1 2 µ = M Z and for a Higgs mass, M H , 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.

Electroweak two-loop corrections to the MW–MZ mass correlation in the Standard Model

“…Previously, corrections from light fermions have only been taken into account via resummations of the one-loop light-fermion contribution (the two-loop light-fermion contributions have been calculated within the MSscheme in Ref. [24]).…”

Complete fermionic two-loop results for the MW–MZ interdependence

“…The considered class of diagrams includes the potentially large corrections both from the top/bottom doublet and from contributions proportional to N lf and N 2 lf , where N lf is the number of light fermions (a partial result for the light-fermion contributions has been obtained in Ref. [18]). The results presented here improve on the previous results of an expansion in m t up to next-to-leading order [13] in containing the full dependence on m t as well as the complete light-fermion contributions at the two-loop order, while in Ref.…”

Hadronic corrections at ${\cal O}(\alpha^2)$ to the energy spectrum of muon decay

“…Besides that, also the O(N f α 2 ) corrections in the Standard Model have been considered in Refs. [8,9].…”