Based on an effective field theory of hadrons in which quantum chromodynamicsis assumed to provide the necessary bare cutoff functions, a gauge-invarianttheory of pion photoproduction with fully dressed nucleons is developed. Theformalism provides consistent dynamical descriptions of pi-N --> pi-Nscattering and Gamma-N --> pi-N production mechanisms in terms of nonlinearintegral equations for fully dressed hadrons. Defining electromagnetic currentsvia the gauging of hadronic n-point Green's functions, dynamically detailedcurrents for dressed nucleons are introduced. The dressed hadron currents andthe pion photoproduction current are explicitly shown to satisfy gaugeinvariance in a self-consistent manner. Approximations are discussed that makethe nonlinear formalism manageable in practice and yet preserve gaugeinvariance. This is achieved by recasting the gauge conditions for allcontributing interaction currents as continuity equations with ``surface''terms for the individual particle legs coming into or going out of the hadronicinteraction region. General procedures are given that approximate any type of(global) interaction current in a gauge-invariance preserving manner as a sumof single-particle ``surface'' currents. It is argued that these prescriptionscarry over to other reactions, irrespective of the number or type ofcontributing hadrons or hadronic systems.
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