The $\gamma \gamma \to {\pi }^0{\pi }^0$ and $\eta \to {\pi }^0\gamma \gamma$ Transitions in the Extended NJL Model

Johan Bijnens, Ansar Fayyazuddin, Joaquim Prades

We calculate within the Extended Nambu--Jona-Lasinio model the leading in $1/N_c$ contribution to $\gamma \gamma \to {\pi }^0{\pi }^0$ to all orders in the external momenta and quark masses. This result…