Chiral symmetry and resonances

A review on the requirements of chiral symmetry on effective quark models is presented. The connection between the pion Salpeter amplitude and the mass gap equation is discussed. Hadronic scattering, notably, $\pi\pi$ scattering is presented. The constraints imposed by chiral symmetry between difractive quark scattering and quark-quark annihilation is presented. Hadronic coupled channels as a consequence of quark-quark annihilation are discussed together with the $^3P_0$ mecahnism. Graphical-rules diagrams are intoduced as a means to evaluate hadronic coupled channel transition potentials. Their role in finding transition potentials responsible, in the scalar sector, for low energy resonances, predicted long ago, and found recently, is also discussed.