Fermion Mass Hierarchy and a High Quality Axion From Gauged U(1) Flavor Symmetry

Abstract

We present a class of models based on a gauged $U(1)_F$ flavor symmetry that explains the hierarchical structure of fermion masses and mixings via the Froggatt-Nielsen (FN) mechanism, while also solving the strong CP problem by the Peccei-Quinn (PQ) mechanism. A global $U(1)_{\rm PQ}$ symmetry with a nonzero QCD anomaly emerges accidentally in this setup as a byproduct of the gauged $U(1)_F$ symmetry. The resulting axion is shown to be of high quality, with the axion potential safeguarded against quantum gravity corrections by the gauge symmetry. Three models, which are generalizations of the Dine-Fischler-Srednicki-Zhitnitsky (DFSZ) axion model, are presented realizing this idea. The right-handed neutrino mass scale is identified as the Froggatt-Nielsen scale in these models. We present explicit UV completions of the FN sectors of these models and show that they preserve the high quality of the axion. In these models, the axion acts as a flavon field, leading to testable predictions in flavor-changing decays of neutral mesons. The axion also serves as the dark matter of the universe with the right amount of relic abundance without causing cosmological domain wall problems. Baryon asymmetry of the universe is realized via leptogenesis which is calculable in these models and found to be of the right order of magnitude.

Figures (27)

• Figure 1: A cartoon depicting the masses of the fundamental particles with their dependence on generation number. The red, green and blue icons denote the masses of the first, second and third generation fermions ParticleDataGroup:2024cfkEsteban:2024eliAntusch:2025fpm. For the neutrino sector we have assumed a normal ordering of the masses. The masses of the Higgs boson and of the gauge bosons $W^{\pm},Z^0$ are shown in light purple, yellow, and orange bands respectively. The massless photon and gluon are depicted on the left side of the figure. Also shown is the range of masses for a QCD axion in blue, with the dark blue band corresponding to axion dark matter denoted as "aDM". Note the presence of a mass desert in the range $(0.1~{\rm eV} - 0.5~{\rm MeV})$.
• Figure 2: Diagrams generating up-type quark Yukawa operators of Model I given in Eq. (\ref{['eq:ModelIUV']}).
• Figure 3: Diagrams generating down type quark and charged lepton Yukawa operators for Model I given in Eq. (\ref{['eq:ModelIUV']}).
• Figure 4: Diagrams generating Dirac and Majorana Neutrino Yukawa operators for Model I given in Eq. (\ref{['eq:ModelIneutrinomass']}).
• Figure 5: Three-loop "propeller" diagram generating the operator of Eq. (\ref{['PQvil-Hud2']}).