π and ρ mesons, and their diquark partners, from a contact interaction

We present a unified Dyson-Schwinger equation treatment of static and electromagnetic properties of pseudoscalar and vector mesons, and scalar and axial-vector diquark correlations, based upon a vector-vector contact interaction. A basic motivation for this paper is the need to document a comparison between the electromagnetic form factors of mesons and those diquarks that play a material role in nucleon structure. A notable result, therefore, is the large degree of similarity between related meson and diquark form factors. The simplicity of the interaction enables computation of the form factors at arbitrarily large spacelike Q(2), which enables us to expose a zero in the rho-meson electric form factor at z(Q)(rho) approximate to root 6m(rho). Notably, r(rho)z(Q)(rho) approximate to r(D)z(Q)(D), where r(rho) and r(D) are, respectively, the electric radii of the rho-meson and deuteron.