Fermion masses and mixing in a 4+1-dimensional SU(5) domain-wall brane model

TL;DR

This paper explores how a 4+1-dimensional SU(5) domain-wall brane model can naturally generate fermion mass hierarchies and mixing angles, addressing limitations of traditional grand unified theories.

Contribution

It demonstrates the potential of a higher-dimensional brane model to produce realistic fermion mass and mixing patterns without electroweak mixing, highlighting the need for flavor symmetry.

Findings

Fermion mass hierarchy can be generated from profile splittings.

CKM matrix generation appears promising in this model.

Realistic lepton mixing angles require fine-tuning or flavor symmetry.

Abstract

We study the fermion mass and mixing hierarchy problems within the context of the SU(5) 4+1d domain-wall brane model of Davies, George and Volkas. In this model, the ordinary fermion mass relations of SU(5) grand unified theories are avoided since the masses are proportional to overlap integrals of the profiles of the electroweak Higgs and the chiral components of each fermion, which are split into different 3+1d hyperplanes according to their hypercharges. We show that the fermion mass hierarchy without electroweak mixing can be generated naturally from these splittings, that generation of the CKM matrix looks promising, and that the Cabibbo angle along with the mass hierarchy can be generated for the case of Majorana neutrinos from a more modest hierarchy of parameters. We also show that under some assumptions made on the parameter space, the generation of realistic lepton mixing angles is not possible without fine-tuning, which argues for a flavour symmetry to enforce the required relations.