Electroweak quantum effects in the MW-MZ relation

Quantum effects in the MW-MZ relation are studied in the framework of the standard SU(2)xU(1) electroweak theory. After reviewing this relation in detail, numerical analysis is carried out by using recent data of ALEPH, DELPHI, L3, OPAL and MARK II collaborations on MZ, and those of CDF and UA2 collaborations on MW. For the weighted average MZexp=91.157±0.032 GeV, the W mass is calculated as MW(0)=80.90±0.04 GeV, MW(l.l)=79.75±0.04±0.02 GeV and MW=80.21±0.04±0.04 GeV at the tree, leading-log and full correction level (for mtop=140 GeV and MHiggs=100 GeV) respectively. Remarkable is that only the fully corrected MW is consistent with MWexp=80.24±0.37 GeV, which clearly demands the heavy top-quark correction, and therefore gives a strong phenomenological support, independent of the neutral current data, to the electroweak theory as a renormalizable quantum field theory with the spontaneous symmetry breakdown. (orig.)