The form factors for the photon to pseudoscalar meson transitions - an update

The form factors for the transitions πγ, ηγ, η'γ and ηcγ are analyzed within the modified perturbative approach in which quark transverse degrees of freedom are retained. The results for the form factors are compared to experiment in detail. As compared to previous calculations within the same approach only little modifications of the meson distribution amplitudes are required in general in order to achieve reasonable agreement with experiment. Only for the πγ form factor a strong contribution from the second Gegenbauer term is found. It also commented on the case of two virtual photons and on the transition form factors in the time-like region. (orig.)