Complete two loop electroweak contributions to the muon lifetime in the Standard Model

An independent result for the two loop fermionic contributions to the muon lifetime in the Standard Model is obtained and slight deviations in the prediction of the W boson mass are found with respect to [Phys. Lett. B 495 (2000) 338; Nucl. Phys. B 632 (2002) 189]. Supplied with the bosonic contributions from [Phys. Rev. Lett. 89 (2002) 241801; ; Phys. Lett. B 551 (2003) 111; ], the shift, due to the complete electroweak contributions, varies from −2.4 to −0.6 MeV. Additionally, a new test of the matching procedure defining the Fermi constant is presented, which uses fermion masses as infrared regulators.