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_F 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_F determined from muon decay, fermion-loop corrections are sufficient for compatibility between theory and experiment.