Two photon decay of the pseudoscalars, the chiral symmetry breaking corrections

The extrapolation of the decay amplitudes of the pseudoscalar mesons into two photons from the soft meson limit where it is obtained from the axial-anomaly to the mass shell involves the contribution of the 0− continuum. These chiral symmetry breaking corrections turn out to be large. The effects of these corrections on the calculated π decay rate, on the values of the singlet-octet mixing angle and on the ratios f8 fπ and f0 fπ are discussed. The implications for the transition form factors γγ∗ −→ π, η, η ′ are also evaluated and confronted with the available experimental data.