Gluon condensation and QCD

Recently it has been argued that in order to fit a large body of experimental data from the viewpoint of QCD it is necessary to assume that gluons can condense. As a first approximation to this problem the author considers in this paper the case where gluons are subjected to intense external sources of colour (which are identified with static c-number quarks). He demonstrates that for sufficiently strong quark sources, gluons find it energetically favourable to undergo boson condensation through a nonperturbative rearrangement of the vacuum state. The basic tecniques that are employed to investigate this problem were first used by Migdal in his study of the related process of pion condensation in dense nuclear matter. However, the generalisation of these techniques to QCD is not straightforward due to the customary complications of preserving the local nonabelian gauge invariance of the theory in any approximations that are made. (Auth.)