Nonperturbative photon q q ¯ light front wave functions from a contact interaction model

We propose a method to calculate the q q ¯ light front wave functions (LFWFs) of photons at low virtuality, i.e., the light front amplitude of γ * → q q ¯ at low Q 2 , based on a light front projection approach. We exemplify this method using a contact interaction model within Dyson-Schwinger equations formalism and obtain the nonperturbative photon q q ¯ LFWFs. In this case, we find the nonperturbative effects are encoded in the enhanced quark mass and a dressing function of covariant quark-photon vertex, as compared to the leading order quantum electrodynamics photon q q ¯ LFWFs. We then use nonperturbative-effect modified photon q q ¯ LFWFs to study the inclusive deep inelastic scattering HERA data in the framework of the color dipole model. The results demonstrate that the theoretical description of data at low Q 2 can be significantly improved once the nonperturbative corrections are included in the photon LFWFs.