π0, η, η' → γγ Decays and the Explicit Chiral Symmetry Breaking.

Corrections to the Wess–Zumino–Witten anomaly caused by the explicit breaking of the chiral symmetry are studied using the effective meson Lagrangian based on the Nambu–Jona-Lasinio model with the simultaneous expansion in derivatives, current quark masses, and 1/Nc powers. The leading contribution and the first correction for the amplitudes of the π0, η, η' → γγ decays and the contact term in the amplitudes have been calculated. The results are compared with similar 1/Nc chiral perturbation calculations and existing experimental data. [ABSTRACT FROM AUTHOR]