$\eta$-Meson Decays and Strong $U_A(1)$ Breaking in the Three-Flavor   Nambu-Jona-Lasinio Model
  We study the $\eta \to \gamma \gamma$ and $\eta \to \pi^0 \gamma \gamma$ decays using an extended three-flavor Nambu-Jona-Lasinio model that includes the 't~Hooft instanton induced interaction. We find that the $\eta$-meson mass, the $\eta \to \gamma \gamma$ decay width and the $\eta \to \pi^0 \gamma \gamma$ decay width are in good agreement with the experimental values when the $U_{A}(1)$ breaking is strong and the flavor $SU(3)$ singlet-octet mixing angle $\theta$ is about zero. The effects of the $U_A(1)$ breaking on the baryon number one and two systems are also studied. 
M. Takizawa (Institute for Nuclear Study, University of Tokyo), Y.   Nemoto and M. Oka (Department of Physics, Tokyo Institu...