We consider phenomenological constraints on the mass M Z Ј and the mixing angles R and of the neutral sector in general SU(2) L ϫSU(2) R ϫU(1) models using electroweak data. The analysis of the neutral sector has the advantage that it has relatively fewer parameters compared to the charged sector since the Cabibbo-Kobayashi-Maskawa matrix elements in the right-handed sector are not involved. We consider the theoretical relations between the gauge boson masses and the mixing angles. We combine the precision electroweak data from CERN LEP I and the low-energy neutral-current experimental data to constrain the parameters in the model. It turns out that M Z Ј Ͼ430 GeV, Ϫ0.00040ϽϽ0.0037, with little constraint on R . Using these constraints, we compare (e ϩ e Ϫ → ϩ Ϫ ), (e ϩ e Ϫ →bb ), and A FB l with the experimental data at LEP II.

The precision measurement on the oscillation of a neutral particle and its antiparticle is very important to probe the footprints of new physics (NP). Although so far no clear signal tells us the existence of NP, Golowich, Pakvasa, and Petrov [1] have recently shown that the NP

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