Yukawa alignment from natural flavor conservation

TL;DR

This paper analyzes the charged Higgs couplings in a three-Higgs-doublet model with natural flavor conservation, showing its equivalence to the Yukawa-aligned two-Higgs-doublet model and exploring extensions with a fourth Higgs doublet.

Contribution

It demonstrates the coupling structure of the three-Higgs-doublet model and its relation to the Yukawa-aligned two-Higgs-doublet model, including the effects of an additional inert Higgs doublet.

Findings

Reproduces the Yukawa-aligned two-Higgs-doublet model coupling structure.

Identifies two constraints from unitarity in the three-doublet model.

Shows that adding a fourth inert Higgs doublet removes these constraints.

Abstract

We study the charged Higgs couplings to fermions in the "democratic" three-Higgs-doublet model, in which one doublet couples to down-type quarks, one to up-type quarks, and one to charged leptons. Flavor-changing neutral Higgs couplings are absent because the Glashow-Weinberg-Paschos condition for natural flavor conservation is in effect. We show that this model reproduces the coupling structure of the charged Higgs boson in the recently-proposed Yukawa-aligned two-Higgs-doublet model, with two subtle constraints that arise from the unitarity of the charged Higgs mixing matrix. Adding a fourth Higgs doublet with no couplings to fermions eliminates these constraints.