Instanton physics in QCD

Abstract

Starting with QCD Lagrangian which is renormalizable and asymptotic free, the chiral symmetry group and functional integral method are reviewed. Instanton and meron solution of classical Yang-Mills field equation are presented. The QCD vacuum is constructed in the absence of fermion. For the vacuum, it is shown in the dilute gas approximation that the chiral symmetry for a phenomenological Lagrangian is broken down. With a more detailed study of QCD vacuum, it is shown that instanton, antiinstanton, and meron pair have a dipolelike behavior and there is a phase transition which leads to bag-like picture in the presence of color source.