Unified relativistic description of piNN and gamma-piNN
  We present a unified description of the relativistic piNN and gamma-piNN systems where the strong interactions are described non-perturbatively by four-dimensional integral equations. A feature of our approach is that the photon is coupled in all possible ways to the strong interaction contributions. Thus the hadronic processes NN -> NN, NN -> pid, pid -> pid, etc. and corresponding electromagnetic processes NN -> gamma-NN, gamma-d -> NN, gamma-d -> pid, ed -> ed, ed -> e'pid, etc., are described simultaneously within the one model of strong interactions. Our formulation obeys two and three-body unitarity, and as photons are coupled everywhere in the strong interaction model, gauge invariance is implemented in the way prescribed by quantum field theory. Our formulation is also free from the overcounting and undercounting problems plaguing four-dimensional descriptions of piNN-like systems. The unified description is achieved through the use of the recently introduced gauging of equations method. 
A. N. Kvinikhidze, B. Blankleider (Flinders University)