The lowest-lying nonet of pseudoscalar mesons consists of the Goldstone boson octet of pions, kaons and the eta, which become massless in the chiral limit of zero quark masses, and the corresponding singlet state, the eta-prime, which, on the other hand, remains a massive state in the chiral limit due to the axial U(1) anomaly.
In order to describe the interactions of the eta-prime with the Goldstone boson octet at low energies, the conventional chiral effective Lagrangian is extended to include the eta-prime. The results presented in this talk include (eta)-(eta-prime) mixing and the dominant decay mode of the eta-prime into (eta bion pion). Furthermore, we conbine the chiral Lagrangian approach with a coupled channel analysis, in order to investigate eta-prime electroproduction off the nucleons.
The investigation of the eta-prime may offer new insights into the role of the axial U(1) anomaly in chiral dynamics.