We consider a generalized linear sigma model with two chiral nonets, one with a quark-antiquark structure, the other one with "diquark-diantiquark" structure. The model aims to explain the existence of a lighter than 1 GeV nonet of scalar mesons. We investigate in this context the masses and mixings of the pseudoscalar and scalar states and find that the lightest pseudoscalar mesons have a large two quark content and the lightest scalar mesons have a large four quark content. The pion-pion scattering is also studied in the limit of massless quarks and for an SU(3) invariant symmetry breaking term. While the current algebra results hold for the first case, they no longer verify for the latter one.
Back to the theory seminar page.