Flaxion: a minimal extension to solve puzzles in the standard model

TL;DR

This paper introduces a minimal extension to the standard model adding a flavon field that explains flavor hierarchies, solves the strong CP problem via the flaxion, and addresses cosmological issues like dark matter, baryogenesis, and inflation.

Contribution

It presents a unified model with a single scalar field that explains flavor structure, solves the strong CP problem, and accounts for key cosmological phenomena.

Findings

The flavon field explains flavor hierarchies in quarks and leptons.

The flaxion solves the strong CP problem and accounts for dark matter.

The flavon’s radial component can serve as inflaton without domain wall issues.

Abstract

We propose a minimal extension of the standard model which includes only one additional complex scalar field, flavon, with flavor-dependent global U(1) symmetry. It not only explains the hierarchical flavor structure in the quark and lepton sector (including neutrino sector), but also solves the strong CP problem by identifying the CP-odd component of the flavon as the QCD axion, which we call flaxion. Furthermore, the flaxion model solves the cosmological puzzles in the standard model, i.e., origin of dark matter, baryon asymmetry of the universe, and inflation. We show that the radial component of the flavon can play the role of inflaton without isocurvature nor domain wall problems. The dark matter abundance can be explained by the flaxion coherent oscillation, while the baryon asymmetry of the universe is generated through leptogenesis.