On the observation of bosonic loop corrections in electroweak precision experiments

We investigate the structure of the experimentally significant electroweak bosonic loop corrections to the leptonic weak mixing angle, the leptonic Z-boson decay width, and the W-boson mass. It is shown that the bosonic corrections that have a sizable effect at the present level of experimental accuracy are directly related to the use of the Fermi constant G(mu) as input parameter for analyzing the LEP observables. Indeed, if the (theoretical value of the) leptonic width of the W boson is used as input parameter instead of the low-energy parameter G(mu) determined from muon decay, fermion-loop corrections are sufficient for compatibility between theory and experiment.