Pion photoproduction through the Δ resonance region: relativistic versus non-relativistic unitary models

A fully relativistic, gauge invariant and unitary pion photoproduction model is constructed including π, ρ, ω, N and Δ degrees of freedom. The model is compared in detail to pion photoproduction observables in view of several sets of high-quality data that were obtained through the Δ resonance region in recent years. Starting from the relativistic model, a non-relativistic model meant for calculations in the nuclear medium is derived. The non-relativistic model is constructed to satisfy unitarity and is applied to both charged and neutral pion photoproduction with the same parameter set. (orig.)