Fitting the $Z b \bar b$ vertex in the two-Higgs-doublet model and in the three-Higgs-doublet model

TL;DR

This paper examines how multi-Higgs-doublet models affect the $Z b ar b$ vertex parameters, identifies issues with experimental fits, and proposes a solution involving light scalars and large Yukawa couplings.

Contribution

It introduces a novel approach to reconcile multi-Higgs-doublet models with experimental data by flipping the sign of $g_R$, requiring specific scalar and coupling conditions.

Findings

Multi-Higgs-doublet models can worsen the fit to $Z b ar b$ data.

A proposed solution involves light scalars and large Yukawa couplings.

The sign of $g_R$ can be reversed to improve the fit.

Abstract

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