Effective theory of QCD and hadron physics

In the fundamental theory of QCD which describes hadrons, the approximate chiral symmetry which exists in the level of Lagrangian is spontaneously broken due to the strong interaction of QCD. In this lecture, the approximate chiral symmetry in the fundamental theory of QCD of strong interaction and its breaking is introduced at first. Then it is explained how to construct the effective theory of 'Hidden Local Symmetry (HLS)' which includes π meson only. As the extension of the chiral perturbation theory, the construction method of effective theory based on the HLS to include vector mesons is presented, and the phenomenological application of finite temperature QCD is given as well. This lecture note is mainly focused on summarizing the construction method of the HLS and its applications. HLS is the effective theory which includes vector mesons including ρ as the HLS gauge boson, in addition to the pseudo scalar mesons such as π which accompanies the spontaneous breaking of chiral symmetry as the Numbu Goldstone particle. Since the gauge symmetry is not explicit but 'hidden' the symmetry breaking pattern is quite similar to QCD if we stand on the overall view point. (S. Funahashi)