Partially flavour non-universal $U(1)$ and radiative fermion masses

TL;DR

This paper proposes a Standard Model extension with a partially flavour non-universal $U(1)$ gauge symmetry that generates lighter fermion masses radiatively, relaxing constraints on new gauge boson masses and predicting observable Higgs couplings deviations.

Contribution

It introduces a minimal anomaly-free $U(1)$ extension with partial flavour universality, enabling radiative fermion mass generation and reducing gauge boson mass bounds.

Findings

Second-generation masses generated by gauge loops

First-generation masses from scalar loops

Higgs couplings largely align with Standard Model

Abstract

We investigate an extension of the Standard Model with a partially flavour non-universal abelian gauge symmetry that enables radiative mass generation for lighter fermions. With flavour-universal charges for the first two generations, gauge-induced loop corrections generate second-generation masses while keeping the first generation massless. Small first-generation masses can arise from subdominant scalar loops within this framework. A single anomaly-free $U(1)$ is sufficient for a realistic model, and the partial universality relaxes the gauge boson mass bound from several thousand TeV to about 200 TeV compared with previous frameworks of this type. We also identify an alignment limit matching the lightest scalar to the observed Higgs and compute its couplings with the fermions, which largely agree with Standard Model values but show testable deviations.