Sequential Flavour Symmetry Breaking

TL;DR

This paper proposes a step-wise symmetry breaking framework in the Standard Model to explain the hierarchical structure of fermion masses and mixing angles through intermediate effective theories.

Contribution

It introduces a novel sequential symmetry breaking approach using spurion fields to connect observed fermion hierarchies to underlying flavor symmetry dynamics.

Findings

Identification of possible flavor symmetry breaking scenarios in the quark sector

Connection between hierarchy of fermion masses and step-wise symmetry breaking

Implications for model building and flavor physics

Abstract

The gauge sector of the Standard Model (SM) exhibits a flavour symmetry which allows for independent unitary transformations of the fermion multiplets. In the SM the flavour symmetry is broken by the Yukawa couplings to the Higgs boson, and the resulting fermion masses and mixing angles show a pronounced hierarchy. In this work we connect the observed hierarchy to a sequence of intermediate effective theories, where the flavour symmetries are broken in a step-wise fashion by vacuum expectation values of suitably constructed spurion fields. We identify the possible scenarios in the quark sector and discuss some implications of this approach.