An Unfamiliar Way to Generate the Hierarchy of Standard Model Fermion Masses

TL;DR

This paper introduces a novel model with multiple Higgs doublets and a family symmetry to explain the fermion mass hierarchy in the Standard Model, predicting a light pseudoscalar and satisfying experimental constraints.

Contribution

It proposes a new approach using a gauged $U(1)$ family symmetry and multiple Higgs doublets to generate fermion mass hierarchies through vacuum expectation values.

Findings

Model satisfies flavor and electroweak constraints.

Predicts a light, weakly coupled pseudoscalar.

Provides a mechanism for fermion mass hierarchy.

Abstract

While the properties of the observed Higgs boson agree with the Standard Model predictions, the hierarchy of fermion masses lacks an explanation within the model. In this work, we propose a fresh approach to this problem, involving a different Higgs doublet responsible for each quark mass. We construct a model with a gauged, non-anomalous $U(1)$ family symmetry that fixes which fermion couples to which doublet with an $\mathcal{O}(1)$ Yukawa coupling. The hierarchy of masses is generated by the hierarchy of vacuum expectation values of the Higgs fields. The model generically predicts a light, weakly coupled pseudoscalar. We verify that the model satisfies constraints from flavour changing neutral currents, Higgs phenomenology and electroweak precision tests.