Exploration of a physical picture for the QCD scalar channel
  A generalized linear sigma model is employed to study the quark structure of low lying scalar as well as pseudoscalar states. The model allows the possible mixing of quark anti-quark states with others made of two quarks and two antiquarks but no a priori assumption is made about the quark contents of the predicted physical states. Effects of SU(3) symmetry breaking are included. The lighter conventional pseudoscalars turn out to be primarily of two quark type whereas the lighter scalars have very large four quark admixtures. 
Amir H. Fariborz, Renata Jora and Joseph Schechter