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

TL;DR

This paper introduces models with a gauged U(1)_F flavor symmetry that explains fermion mass hierarchies, naturally produces a high-quality axion solving the strong CP problem, and links axion physics with flavor and cosmology.

Contribution

The paper presents new models combining flavor symmetry and axion solutions, with explicit UV completions and testable flavor-changing decay predictions.

Findings

High-quality axion protected by gauge symmetry

Fermion mass hierarchies explained via Froggatt-Nielsen mechanism

Axion as dark matter with correct relic abundance

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.