ABSTRACT
The theory of strong interactions, quantum chromodynamics, is based on the colour group which acts on the so-called colour indices of the quarks. Each flavour of quark comes in three ‘colours’ labelled 1, 2, 3 which form a basis for the three-dimensional representation of colour. This chapter discusses a general simple gauge group with the example of quantum chromodynamics. It describes an analogous situation which arises in connection with ordinary integrals rather than path integrals and discusses the path integral for zero source terms. The two most frequently used gauges are Feynman gauge and Landau gauge. The Landau gauge also has advantages in theories with Higgs scalar mesons, because the scalars decouple from the Faddeev–Popov ghosts in this gauge.
