Fitting the Zb b ¯ $$ Zb\overline{b} $$ vertex in the two-Higgs-doublet model and in the three-Higgs-doublet model

We investigate the new contributions to the parameters gL and gR of the $$ Zb\overline{b} $$ vertex in a multi-Higgs-doublet model (MHDM). We emphasize that those contributions generally worsen the fit of those parameters to the experimental data. We propose a solution to this problem, wherein gR has the opposite sign from the one predicted by the Standard Model; this solution, though, necessitates light scalars and large Yukawa couplings in the MHDM.