Perturbative approach to U_A(1) breaking
  The six-quark instanton induced 't Hooft interaction is considered in combination with the Nambu-Jona-Lasinio (NJL) type U_L(3)X U_R(3) chiral symmetric Lagrangian. We discuss the bosonization of this multi-quark interaction, taking the U_A(1) breaking as a perturbation. We discuss its relation with the usual approach. 
Brigitte Hiller, Alexander A. Osipov, Alex H. Blin