How unique are SU(5) and SO(10) grand unified theories?

Abstract

We find that SU(5) and SO(10) grand unified theories are almost uniquely chosen under the major ansatz: only left-handed particles in SU(2) doublets and their antiparticles in SU(2) singlets. We have not used any information on the color group, family structures, or quarklepton correspondence, etc., at all. The consequence of grand unification is that the color group is SU(3), quarks come in color triplet, and their electric charges are $\frac{2}{3}$ and $-\frac{1}{3}$.