Two-gluon components of the η and η′ mesons to leading-twist accuracy -: art. no. 054017

We critically reexamine the formalism for treating the leading-twist contributions from the two-gluon Fock components occurring in hard processes that involve eta and eta' mesons and establish a consistent set of conventions for the definition of the gluon distribution amplitude, the anomalous dimensions, as well as the projector of a two-gluon state onto an eta or eta' state. We calculate the eta, eta'-photon transition form factor to order alpha(s) and show the cancellation of the collinear and UV singularities explicitly. An estimate of the lowest Gegenbauer coefficients of the gluon and quark distribution amplitudes is obtained from a fit to the eta, eta'-photon transition form factor data. In order to elucidate the role of the two-gluon Fock component further, we analyze electroproduction of eta, eta' mesons and the g*g* eta(eta') vertex.