Non-perturbative methods in QCD

In these lectures methods and models will be described for treating non-perturbative QCD which are based on peculiar assumptions of the ground state of QCD, the physical vacuum. First the evidence for non-trivial structures in the QCD-vacuum will be shortly presented, based on the sum-rule method of QCD. This leads to the introduction of local condensates, such as the gluon or quark condensates. The consequences of giving these local expectation values more structure will be furthermore explored, i.e. making non-local. A model proposed and advocated by Yuri Simonov and the author since 1987 will also be presented, and some special applications of the model and consistency checks will be given. It will turns out that confinement in a pure non-Abelian gauge theory is a simple consequence of the model, but that chiral symmetry breaking is very hard to incorporate. The applications that will be discussed are therefore chosen in such a way that QCD properties related to chiral symmetry breaking are of no importance. In the first part of the applications only static quark effects will be studied and in the second part, those of very fast ones which are practically frozen on light like paths. Although the model of the stochastic vacuum plays a central role in this presentation, several techniques will be presented which are useful for non-perturbative QCD in general