Covariant Classification Scheme of Hadrons and Chiral States

The essential points and physical backgrounds of the covariant level-classification scheme, recently proposed by us, are reviewed: In this scheme the general composite hadrons are classified as the multiplets with the U(12)SF * O(3,1) symmetry, where U(12)SF supset U(4)D.S. * SU(3)F, and U(4)D.S. is a homogeneous Lorentz transformation group for Dirac spinors. This symmetry predicts the existence of new type of chiral mesons and baryons out of the conventional level classification scheme. The sigma nonet is a typical example of chiralons to be assigned to the q bar q relativistic S-wave state.