We motivate and explore the possibility that extra SU(N) gauge groups may exist independently of the Standard Model groups, yet not be subgroups of some grand unified group. We study the running of the coupling constants as a potential evidence for a common origin of all the gauge theories. Several different example are displayed. Some of the multiple options involve physics at the TeV scale.
Donoghue, JF and Pais, P, "Gauge federation as an alternative to unification" (2009). PHYSICAL REVIEW D. 91.