The flavor puzzle in multi-Higgs models

TL;DR

This paper investigates flavor hierarchies in two-Higgs-doublet models, identifying minimal constraints on Yukawa couplings that produce observed mass patterns with less tuning than the Standard Model.

Contribution

It introduces flavor basis independent constraints on Yukawa couplings in multi-Higgs models, extending from toy models to the full Standard Model.

Findings

Two constraints are sufficient to generate the observed mass hierarchy.

Yukawa couplings require only about 10% tuning, less than in the Standard Model.

Flavor changing currents are manageable in the near-decoupling limit.

Abstract

We reconsider the flavor problem in the models with two Higgs doublets. By studying two generation toy models, we look for flavor basis independent constraints on Yukawa couplings that will give us the mass hierarchy while keeping all Yukawa couplings of the same order. We then generalize our findings to the full three generation Standard Model. We find that we need two constraints on the Yukawa couplings to generate the observed mass hierarchy, and a slight tuning of Yukawa couplings of order 10%, much less than the Standard Model. We briefly study how these constraints can be realized, and show how flavor changing currents are under control for $K-\bar{K}$ mixing in the near-decoupling limit.