Doublet-Triplet Splitting and Fermion Masses with Extra Dimensions

TL;DR

This paper demonstrates how extra-dimensional brane models can naturally solve the doublet-triplet splitting problem and generate realistic fermion masses without flavor symmetry, using the pseudo-Goldstone boson mechanism.

Contribution

It introduces a novel extra-dimensional framework implementing the pseudo-Goldstone boson mechanism for doublet-triplet splitting with realistic fermion masses.

Findings

Realistic fermion mass and mixing patterns achieved

Neutrino masses compatible with solar and atmospheric data

Extra-dimensional geometry explains coupling hierarchies

Abstract

The pseudo-Goldstone boson mechanism for the ``doublet-triplet splitting'' problem of the grand unified theory can be naturally implemented in the scenario with extra dimensions and branes. The two SU(6) global symmetries of the Higgs sector are located on two separate branes while the SU(6) gauge symmetry is in the bulk. After including several vector-like fields in the bulk, and allowing the most general interactions with their natural strength (including the higher dimensional ones which may be generated by gravity) which are consistent with the geometry, a realistic pattern of the Standard Model fermion masses and mixings can be naturally obtained without any flavor symmetry. Neutrino masses and mixings required for the solar and atmospheric neutrino problems can also be accommodated. The geometry of extra dimensions and branes provides another way to realize the absence of certain interactions (as required in the pseudo-Goldstone boson mechanism) or the smallness of some couplings (e.g., the Yukawa couplings between the fermions and the Higgs bosons), in addition to the usual symmetry arguments.