Radiative corrections to the Z b b-bar vertex and constraints on extended Higgs sectors
Abstract
We explore the radiative corrections to the process Z --> b b-bar in models with extended Higgs sectors. The observables Rb (the Z hadronic branching fraction to b b-bar) and the b-quark asymmetry Ab = (gL2 - gR2)/(gL2 + gR2) are sensitive to these corrections. We find that in models containing only Higgs doublets, singlets, or larger multiplets constrained by a custodial SU(2) symmetry, the radiative corrections to Rb involving charged Higgs bosons always worsen the Standard Model fit to electroweak data. Thus, the present Rb data can be used to set lower bounds on the charged Higgs masses in such models. Radiative corrections to Rb involving light neutral Higgs bosons in models with enhanced couplings to b b-bar can improve the Standard Model fit to present data. The Higgs sector alone cannot explain a significant deviation of Ab from its Standard Model prediction. We present general formulas for the corrections to Rb and Ab in an SU(2)xU(1) electroweak model with an arbitrary extended Higgs sector, and derive explicit results for a number of specific models.
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