An $SU(15)$ Approach to Bifermion Classification
One interesting way to extend the standard model is the hypothesis of bifermions which are bosons which couple to pairs of quarks and leptons. We point out that $SU(15)$ grand unification gives a natural way to classify bifermions and discuss leptoquarks, biquarks and bileptons. In fact, $SU(15)$ provides an ideal covering group as it contains all possible bifermions within a single model.
hep-ph↗