ϒ ϒ→ π0π0 and η → π0ψψ at low energy within the extended Nambu Jona-Lasinio model Original Research Article

Within the Extended Nambu Jona-Lasinio model, we calculate the O(π6) counterterms entering the low-energy expansion of the ψψ → π0π0 and the η → π0ψψ amplitudes in Chiral Perturbation Theory. For ψψ → π0π0 our results are compatible with both the experimental data and the two-loop calculation using meson resonance saturation. For the η decay we find Φ(η → π0ψψ) = 0.58 ± 0.3 eV which is in agreement with experiment within one standard deviation. We also give predictions for the neutral pion polarizabilities and compare them with the results obtained from resonance saturation.