Theoretical Advanced Study Institute in Elementary Particle Physics, ed. by P
- W. Hollik
- Phys. Letters
Based on recent W -mass measurements, the electroweak theory is tested at non-trivial quantum correction level, i.e., beyond the Born approximation with α(MZ) instead of α. We can conclude that some non-Born type corrections must exist at more than 92 % confidence level, and the non-decoupling top-quark corrections are required at 97 % confidence level. E-mail (BITNET) address: A52071@JPNKUDPC or HIOKI@JPNYITP Electroweak precision analyses have been performed extensively ever since high-energy experiments at MW,Z scale started at CERN, FNAL and SLAC. In particular, quite lots of precise data on the Z boson from LEP have made it possible to test the standard electroweak theory with considerable accuracy. Thereby, many particle physicists now believe that this theory (plus QCD) describes correctly phenomena below O(10) GeV. Recently, however, Novikov et al. claimed that the Born approximation based on α(MZ) instead of α(=1/137.036) reproduces all electroweak precision measurements within the 1σ accuracy . This means that the electroweak theory has not yet been tested at “non-trivial” level (although I never think testing the α(MZ) effects to be trivial). Concerning this problem, Sirlin stressed that such a non-trivial test is possible through low-energy hadron physics . In fact, his conclusion is that there is very strong evidence for non-Born effects in the analysis of the unitarity of the Kobayashi-Maskawa mixing matrix. He also pointed out that more precise measurements of MW and the on-resonance asymmetries are crucial for high-energy tests. In this short note, I will study the same issue based on the recent W -mass determination by CDF combined with UA2 data : M W = 80.30± 0.20 GeV. (1) More concretely, I will examine whether the Born approximation still works or not, and then focus on the top-quark contribution which does not decouple, i.e., becomes larger and larger as mt increases. It is very significant to test it because the existence of such effects is a characteristic feature of theories in which particle masses are produced through spontaneous symmetry breakdown plus large Yukawa couplings. First, it is quite easy to see if taking only α(MZ) into account is still a good There are a lot of papers on this subject. I only cite  among the latest articles here (see also [2, 3] and the references cited therein).