Exploring a Gauge Horizontal Model for Charged Fermion Masses

TL;DR

This paper proposes a gauge horizontal symmetry extension of the Standard Model that naturally explains charged fermion mass hierarchies and mixing patterns without requiring extra colored fermions, predicting distinctive experimental signatures.

Contribution

It introduces an anomaly-free gauge $U(1)$ horizontal symmetry model with novel mass generation mechanisms for all fermion generations, avoiding additional colored fermions and ensuring automatic suppression of certain CP-violating effects.

Findings

First-generation fermion masses arise from radiative corrections.

Electron EDM vanishes at two-loop level, no charged lepton flavor violation.

Model predicts unique collider signatures and gauge boson decay patterns.

Abstract

We investigate an extension of the Standard Model (SM) incorporating a gauge $ U(1) $ horizontal symmetry that is free of anomalies. This extension introduces four additional un-Higgsed scalar doublets that do not develop vacuum expectation values, two scalar singlets, and a pair of vector-like fermionic singlets. Within this framework, the masses of third-generation charged fermions are generated through the conventional SM Yukawa interactions, while the masses of second-generation charged fermions are suppressed via a mechanism reminiscent of Froggatt-Nielsen. In contrast, the masses of first-generation charged fermions are predominantly determined by radiative corrections. Unlike traditional implementations of the Froggatt-Nielsen mechanism, our model does not require additional colored vector or chiral fermions beyond the SM. This model provides an economical ultraviolet-complete mechanism to explain the observed patterns in charged fermion masses and Cabibbo-Kobayashi-Maskawa matrix elements. Notably, the electron electric dipole moment vanishes automatically at the two-loop level, and there is no charged lepton flavor violation to all orders. We also discuss potential experimental signatures that could distinguish this model from other $ Z' $ models, such as specific patterns in gauge boson decays and associated collider signatures.