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In light of recent experimental results, we revisit the dispersive analysis of the ω → 3 π decay amplitude and of the ω π 0 transition form factor. Within the framework of the Khuri–Treiman equations, we show that the ω → 3 π Dalitz-plot parameters obtained with a once-subtracted amplitude are in agreement with the latest experimental determination by BESIII. Furthermore, we show that at low energies the ω π 0 transition form factor obtained from our determination of the ω → 3 π amplitude is consistent with the data from MAMI and NA60 experiments. [ABSTRACT FROM AUTHOR]

We study the reactions γγ→ π π, π π, $K^{0}\bar{K}^{0}$, K K, ηη and π η based on a chiral Lagrangian with dynamical light vector mesons as formulated within the hadrogenesis conjecture. At present our chiral Lagrangian contains five unknown parameters that are relevant for the photon-fusion reactions. They parameterize the strength of interaction terms involving two vector meson fields. These parameters are fitted to photon-fusion data γγ→ π π, π π, π η and to the decay η→ π γγ. In order to derive gauge invariant reaction amplitudes in the resonance region constraints from maximal analyticity and exact coupled-channel unitarity are used. Our results are in good agreement with the existing experimental data from threshold up to about 0.9 GeV for the two-pion final states. The a meson in the π η channel is dynamically generated and an accurate reproduction of the γγ→ π η data is achieved up to 1.2 GeV. Based on our parameter sets we predict the γγ→ $K^{0}\bar{K}^{0}$, K K, ηη cross sections. [ABSTRACT FROM AUTHOR]