Quarks as Vortices in Vacuum

Despite the many successes of QCD much of low energy hadronic physics cannot be extracted from the first principles of the theory. Quarks were first postulated as constituents of hadrons with masses about hundreds of MeV to describe the spectroscopy of hadrons. Subsequently, it was realized that hard processes are the arena of current quark considerations with masses much lighter than the original constituent ones. Relationship between current and constituent quarks is still smooth and unclear. According to the modern picture of hadrons quark-antiquark in mesons and three valence quarks in nucleons are dressed with gluons and ”sea” quark-antiquark pairs in such a way that they become much heavier, although the dynamical mechanism of dressing is not understood definitely.