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 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$SU(3) \times SU(3)$$\end{document} 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 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\eta {\text{/}}\eta {\kern 1pt} ' \to {{\pi }^{ + }}{{\pi }^{ - }}\gamma $$\end{document} amplitudes have been calculated. The results are compared with similar 1/Nc chiral perturbation calculations and existing experimental data.