Constraints on two-Higgs-doublet models at large $\tan \beta$ from W and Z decays

We study constraints on type-II two-Higgs-doublet models at large $\tan \beta$ from CERN LEP and SLD Z-pole data and from lepton universality violation in W decay. We perform a global fit and find that, in the context of Z decay, the LEP–SLD experimental values for lepton universality violation, $R_b,$ and $A_b$ all somewhat disfavor the model. Contributions from the neutral-Higgs sector can be used to constrain the scalar–pseudoscalar Higgs mass splittings. Contributions from the charged-Higgs sector allow us to constrain the charged-Higgs boson mass. For $\tan \beta =100\mathrm{}$ we obtain the 1σ classical (Bayesian) bounds of $m_{H^{\pm }}>~670\mathrm{GeV}\hspace{0.5em}\left(370\mathrm{}\mathrm{GeV}\right)$ and $1>~m_{h^0}{/m}_{A^0}{|}_{\alpha =\beta }{=m}_{H^0}{/m}_{A^0}{|}_{\alpha =0\mathrm{}}>~0.68\hspace{0.5em}\mathrm{}\left(0.64\right).$ The 2σ bounds are weak. Currently, the Fermilab Tevatron experimental limits on lepton universality violation in W decay provide no significant constraint on the Higgs sector.