Narrow Results

We study the dependence of meson masses and decay constants on the up, down and strange quark masses in QCD in terms of an effective field theory approach. The role of dynamical vector meson degrees of freedom is scrutinized by a one-loop approximation to the self-energies of the Goldstone bosons and vector mesons as well as the decay constants of the Goldstone bosons. Our results are confronted with QCD lattice data from various lattice groups. From a successful global fit to such lattice data we are lead to the conclusion that dynamical vector mesons imply significant changes in the Gasser and Leutwylers low-energy constants.

We use th Interacting Instanton Liquid Model to investigate the non-perturbative interaction associated to spontaneous chiral symmetry breaking. In particular, we study how hadrons' structure changes as a function of the quark mass. To support the validity of this model in the chiral regime, the quark mass dependencies of several properties are shown to agree with chiral perturbation theory, including the density of eigenmodes of the Dirac operator and the masses of the pion and nucleon. We identify a natural mass scale m* = 80 MeV which sets the boundary of the mass regime where the non-perturbative QCD dynamics is determined by chiral effects.