In Part III, unified gauge theories of the electroweak interaction of particles have been presented. This chapter deals with unified gauge models of strong, electromagnetic, and weak interactions. Constructing such models is based on the fact that, as will be demonstrated below, the effective coupling constants of various groups behave differently with increasing energy: the coupling constants of the groups SU3 and SU2 decrease (the former more rapidly than the latter), while the coupling constant of the group U1 increases (Fig. 14.1). As a consequence, it may be expected that at sufficiently large energies all three constants will coincide. Models with a single coupling constant in the high energy range are thus conceivable. The unification procedure resulting in the coincidence of the coupling constants of strong, electromagnetic, and weak interactions at a certain high energy is known as grand unification. The grand-unification group is broken by the Higgs fields in the presently accessible energy range so that it manifests itself as the direct product of the group of the strong, electromagnetic, and weak interactions (e.g., SU3×SU2×U1).
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