Radiative corrections to the Zb(b)over-bar vertex and constraints on extended Higgs sectors -: art. no. 015011

We explore the radiative corrections to the process Z-->b (b) over bar in models with extended Higgs sectors. The observables R-b = Gamma(Z --> b (b) over bar)/Gamma(Z --> hadrons) and the Zb (b) over bar coupling asymmetry, A(b) = (g(L)(2) - g(R)(2))/(g(L)(2) + g(R)(2)), are sensitive to these corrections. We present general formulas for the one-loop corrections to R-b and A(b) in an arbitrary extended Higgs sector, and derive explicit results for a number of specific models. We find that in models containing only doublers, singlets, or larger multiplets constrained by a custodial SU(2)(c) symmetry, so that M-W = M-Z cos theta(W) at tree level, the one-loop corrections due to virtual charged Higgs bosons always worsen agreement with experiment. The R-b measurement can be used to set lower bounds on the charged Higgs boson masses. Constraints on models due to the one-loop contributions of neutral Higgs bosons are also examined.