ABSTRACT
The goal of grand unification is to unify the strong, weak, and electromagnetic interactions and the quarks and leptons within the framework of a gauge field theory based upon a simple or semi-simple, non-Abelian symmetry group. Such theories make two startling predictions: new interactions that violate baryon number (B) and lepton number (L) and thereby lead to the instability of the proton, and the existence of stable, superheavy magnetic monopoles. Both predictions have very significant cosmological consequences. The B-violating interactions are today apparently very, very weak as evidenced by the longevity of the proton. Within the framework of baryogenesis one would expect that the magnitude of the lepton asymmetry which evolves is comparable to that of the baryon asymmetry. The baryogenesis scenario is one of the great triumphs of particle cosmology, and in the absence of direct evidence for proton decay, baryogenesis may provide the strongest, albeit indirect, evidence for some kind of unification of the quarks and leptons.
