Radiative corrections to the Z b b-bar vertex and constraints on extended Higgs sectors

Preprint

11 June 1999

preprint
Published by arXiv in arXiv

https://doi.org/10.48550/arXiv.hep-ph/9906332

Abstract

We explore the radiative corrections to the process Z --> b b-bar in models with extended Higgs sectors. The observables R_b (the Z hadronic branching fraction to b b-bar) and the b-quark asymmetry A_b = (g_L^2 - g_R^2)/(g_L^2 + g_R^2) 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 R_b involving charged Higgs bosons always worsen the Standard Model fit to electroweak data. Thus, the present R_b data can be used to set lower bounds on the charged Higgs masses in such models. Radiative corrections to R_b 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 A_b from its Standard Model prediction. We present general formulas for the corrections to R_b and A_b 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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