Process eta -> pi^0 gamma gamma in the Nambu-Jona-Lasinio model
  The decay width of the process eta -> pi^0 gamma gamma is calculated in the framework of the Nambu-Jona-Lasinio model. The momentum dependence of quark loops is taken into account. Three types of diagrams are considered: quark box, scalar(a0) and vector(rho, omega) pole diagrams. The obtained estimations are in satisfactory agreement with recent experimental data. 
A. E. Radzhabov and M. K. Volkov