Proton Decay in Teravolt Unification
  Model building based on abelian quiver gauge theories gives models which resemble trinification, originally proposed with yottavolt unification. However, unification occurs in the teravolt range so proton decay must be completely excluded in the scalar sector. It is straightforward to accomplish this by a discrete symmetry which is a generalized baryon number B. Unlike in trinification, this is possible because quarks and leptons acquire masses from relevant operators which appear in four-dimensional conformal symmetry breaking. 
P.H. frampton