Variants of the Standard Model with Electroweak-Singlet Quarks

TL;DR

This paper explores theoretical models with electroweak-singlet quarks, revealing unique properties like charged nucleons and absence of neutral leptons, to understand why such fermions are not observed in the Standard Model.

Contribution

It constructs and analyzes hypothetical models with electroweak-singlet quarks, highlighting their distinctive features and potential origins from grand unified theories.

Findings

Models lack neutral leptons.

Both proton and neutron-like particles are charged.

Exotic properties emerge in grand unified contexts.

Abstract

The successful description of current data provided by the Standard Model includes fundamental fermions that are color-singlets and electroweak-nonsinglets, but no fermions that are electroweak-singlets and color-nonsinglets. In an effort to understand the absence of such fermions, we construct and study {\it gedanken} models that do contain electroweak-singlet chiral quark fields. These models exhibit several distinctive properties, including the absence of any neutral lepton and the fact that both the $(uud)$ and $(ddu)$ nucleons are electrically charged. We also explore how such models could arise as low-energy limits of grand unified theories and, in this more restrictive context, we show that they exhibit further exotic properties.