Number of fermion generations from a novel Grand Unified model

TL;DR

This paper explores a novel Grand Unified Theory based on an SU(9) gauge group that can naturally explain why there are three fermion generations, using specific fermion representations and unification constraints.

Contribution

The paper introduces a new SU(9) GUT model with specific fermion representations that successfully predicts the number of fermion generations.

Findings

SU(9) model can unify electroweak and strong interactions

Fermions in antisymmetric rank-1 and rank-3 representations

Constraints on fermion masses from unification requirements

Abstract

Electroweak interactions based on a gauge group $\rm SU(3)_L \times U(1)_X$, coupled to the QCD gauge group $\rm SU(3)_c$, can predict the number of generations to be multiples of three. We first try to unify these models within SU(N) groups, using antisymmetric tensor representations only. After examining why these attempts fail, we continue to search for an SU(N) GUT that can explain the number of fermion generations. We show that such a model can be found for $N=9$, with fermions in antisymmetric rank-1 and rank-3 representations only, and examine the constraints on various masses in the model coming from the requirement of unification.