Bounds on anomalous three-gauge boson couplings from the “heavy” Zbb vertex

We derive bounds on anomalous ZWW couplings, assuming that the residual apparent small discrepancy between the experimental and the MSM values of the ratio Rb = Γb/Γh of the Z widths into bb and into hadrons is entirely due to the “heavy” quark component of the Zbb vertex. The m12 dependence of this quantity selects the Goldstone H± (or longitudinal W±) components of the anomalous couplings, and greatly reduces the number of involved parameters. For Λ of order 1 TeV we find the conservative 1 − σ bound −0.40⩽ (fwMZ2/2Λ2−0.04fBMZ2/2Λ2) ⩽ −0.15, that would lead to observable effects at LEP2.