Radiative Mass Generation in Gauged Theories of Flavour: A Path to Fermion Mass Hierarchies

TL;DR

This paper proposes models with extended gauged flavour symmetries where fermion masses are generated radiatively, naturally explaining the mass hierarchy by assigning tree-level masses only to third-generation fermions and quantum corrections to lighter generations.

Contribution

It introduces new gauged flavour symmetry models, including Abelian and non-Abelian extensions, that realize radiative fermion mass generation and explain the SM mass hierarchy.

Findings

Abelian extensions can generate second-generation masses at 1-loop.

Non-Abelian $SU(3)_F$ models are more predictive with fewer parameters.

A $U(1)_F$ extension predicts new physics around 10^3 TeV.

Abstract

We present a class of models based on extended gauged flavour symmetries that address the hierarchical structure of fermion masses in the Standard Model (SM) through the radiative mass generation mechanism. In these frameworks, only third-generation fermions acquire tree-level masses, while the first and second generations gain their masses via quantum corrections induced by new gauge bosons, naturally explaining the observed mass hierarchy. Since the technically natural structure of fermion masses in the SM prevents such a mechanism from being implemented directly, we propose extensions involving both Abelian and non-Abelian gauge symmetries. Abelian extensions, which must be flavour non-universal, typically generate masses for only second-generation fermions at the 1-loop level, requiring higher order corrections or extension of gauge structure to account for first-generation masses. We show that either a $U(1)_1 \times U(1)_2$ extension or a single $U(1)_F$ with up to 2-loop mass generation can successfully realize the mechanism, with the latter predicting a viable new physics scale around $10^3$ TeV when flavour-violating charges are optimized. Non-Abelian extensions, such as those based on $SU(3)_F$, provide a more constrained and predictive setup due to a comparatively fewer number of free parameters. We also explore a radiative mechanism in Abelian extensions within left-right symmetric theories, which simultaneously addresses the strong CP problem. All these models collectively offer a compelling and testable framework for generating a realistic SM fermion mass spectrum.