NONPERTURBATIVE ASPECTS OF THE QUARK-PHOTON VERTEX

The electromagnetic interaction with quarks is investigated through a relativistic, electromagnetic gauge-invariant treatment. Gluon dressing of the quark-photon vertex and the quark self-energy functions is described by the inhomogeneous Bethe-Salpeter equation in the ladder approximation and the Schwinger-Dyson equation in the rainbow approximation, respectively. Results for the calculation of the quark-photon vertex are presented in both the timelike and spacelike regions of photon momentum squared; however, emphasis is placed on the spacelike region relevant to electron scattering. The treatment presented here simultaneously addresses the role of dynamically generated qq̄ vector bound states and the approach to asymptotic behavior. The resulting description is therefore applicable over the entire range of momentum transfers available in electron scattering experiments. Input parameters are limited to the model gluon two-point function, which is chosen to reflect confinement and asymptotic freedom, and are largely constrained by the obtained bound-state spectrum. © 1995 The American Physical Society.