Studies of gauge field theories in terms of local gauge-invariant quantities

In the framework of the functional-integral approach to quantum gauge field theories in the present thesis a quantization procedure in terms of gauge-invariant fields is proposed and realized on the example of two- and four-dimensional Abelian models (Thirring model and QED) as well as the one-flavour QCD. For this the algebra of from the gauge-dependent field configuration of the basing quantum field theory formed gauge-invariant Grassmann-algebra valued differential forms, which carries the structure of a Z2-graded differential algebra, is studied in more detail. Thereafter follows the implementation of a suitable chosen set of gauge-invariant fields as well as certain algebraic relations into the functional integral, by which the original gauge-dependent field configuration can be integrated out. This procedure called ''reduction of the functional integral'' leads finally to an effective bosonized (quantum) theory of interacting gauge-invariant and by this physical fields. The presented procedure can be considered as general bosonization scheme for quantum field theories in arbitrary space-time dimensions. The physical evaluation of the obtained effective theories is demonstrated on the example of the calculation of the chiral anomaly as well as certain vacuum expectation values in the framework of the studied Abelian models. As it is thereby shown one is confronted with a series of novel phenomena and problems, which allow at suitable treatment deeper insights in non-perturbative questions