Prediction for Z-mass is a crucial test of the standard model

Abstract

In schemes with one W boson and two Z-bosons (mediating the charged and neutral current interactions involving ordinary fermions) based on the direct product and simple groups, SU(2) × U(I) x u'(l) and G × U(1) (G is a simple group of rank two), the following two questions are discussed. (1) What are the necessary and sufficient conditions for minimal reducibility of the effective four-fermion neutral current interaction (involving v~-hadron, electron-hadron and yr.-electron sectors) to the corresponding prediction of the standard model? (2) In what way are the masses of the two Z-~'osons constrained relatixe to the mass of the neutral boson of standard moael? The answers to these questiors are given first by keeping the underlying Higgs structure, responsible for gauge-boson (and fermion) mass generation, comple- tely arbitrary (called Higgs-indeFendent and then by making a specific choice for the Higgs structure resulting in a natura! mass relation for the W and Z-bosons 2 that is an exact counterpart to Mw(s)= Mz(s)seC 0 w for the standard model (called Higgs-dependent case). The distinction lzet~cen these two cases is brought out clearly as also that Izetween the direct product and simple groups. Whether or not any assumption is made about the Higgs structure, with eitEer the direct product or the simple group, it is concluded that in general there is a Z-boson lighter than the neutral boson of the standard model.