On the effect of resonances in the quark-photon vertex

Understand

A calculation of hadronic timelike form factors in the Poincar\'e-covariant Bethe-Salpeter formalism necessitates knowing the analytic structure of the non-perturbative quark-photon vertex in the context of the Poincar\'e-covariant Bethe-Salpeter formalism.

• We include, in the interaction between quark and antiquark, the possibility of non-valence effects by introducing pions as explicit degrees of freedom.
• These encode the presence of intermediate resonances in the Bethe-Salpeter interaction kernel.
• We calculate the vertex for real as well as complex photon momentum.