Nonperturbative Flow Equations and Low--Energy QCD
  We review the formalism of the effective average action in quantum field theory which corresponds to a coarse grained free energy in statistical mechanics. The associated exact renormalization group equation and possible nonperturbative approximations for its solution are discussed. This is applied to QCD where one observes the consecutive emergence of mesonic bound states and spontaneous chiral symmetry breaking as the coarse graining scale is lowered. We finally present a study of the phenomenological importance of non--renormalizable terms in the effective linear meson model. 
D.-U. Jungnickel and C. Wetterich (ITP Heidelberg)