Gauge Theories and Quantum-Chromodynamics

Abstract

Nowadays the common model of quark-quark interactions is an SU(3) gauge theory in a degree of freedom, arbitrarily called “color”. There are by now many experimental facts supporting this model, as we shall discuss later in more detail. It seems by now also to be proven that QCD (quantum chromodynamics) is able to correctly describe the most pronounced feature of quark-quark interactions, i.e., confinement, and that it will generate, for example the correct hadron masses. The results obtained so far are all compatible with the phenomenological properties, but in many cases the accuracy of theoretical calculations is still rather low. Typical uncertainties for hadron masses, for example, are 10 percent. In fact, the general acceptance of QCD is based not only on its own achievements, but also to a large extent on the outstanding success of the gauge theory of weak and electromagnetic interactions. For this reason we begin with a brief overview of the Glashow—Salam—Weinberg model. (The Glashow—Salam—Weinberg model combined with QCD is usually called the standard model). The typical features of gauge theories are discussed in the context of this specific model.