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

Abstract

We investigate the new contributions to the parameters $g_L$ and $g_R$ of the $Zb\bar{b}$ 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 $g_R$ 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.

Comments: 30 pages, 13 figures; v2: added two footnotes and two references; v3: modified 4 figures and added 3 new figures, all sections have changes, added new appendix and added references; v4 matches published version