Dynamical coupled-channels model study of pion photoproduction
  The photoproduction of pion off nucleon is investigated within a dynamical coupled-channels approach based on the Juelich pi-N model, which has been quite successful in the description of pi-N to pi-N scattering for center-of-mass energies up to 1.9 GeV. The full pion photoproduction amplitude is constructed to satisfy the generalized Ward-Takahashi identity and hence, it is fully gauge invariant. The calculated differential cross sections and photon spin asymmetries up to 1.65 GeV center-of-mass energy for the reactions gamma p to pi^+ n, gamma p to pi^0 p and gamma n to pi^- p are in good agreement with the experimental data. 
F. Huang, M. D\"oring, H. Haberzettl, J. Haidenbauer, C. Hanhart, S.   Krewald, U.-G. Mei{\ss}ner, K. Nakayama
nucl-th