  The charged and neutral pion photoproduction reactions are investigated in a
dynamical coupled-channels approach based on the formulation of Haberzettl,
Huang, and Nakayama [Phys. Rev. C 83, 065502 (2011)]. The hadronic final-state
interaction is provided by the Juelich pi-N model, which includes the channels
pi-N and eta-N comprising stable hadrons as well as the effective pi-pi-N
channels pi-Delta, sigma-N, and rho-N. This hadronic model has been quite
successful in describing pi-N to pi-N scattering for center-of-mass energies up
to 1.9 GeV. By construction, the full pion photoproduction current satisfies
the generalized Ward-Takahashi identity and thus is gauge invariant as a matter
of course. 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 pi0 p, gamma n to pi- p and gamma n to pi0 n are in good
agreement with the experimental data.
