Gauge-invariant meson photoproduction with extended nucleons
  The general gauge-invariant photoproduction formalism given by Haberzettl is applied to kaon photoproduction off the nucleon at the tree level, with form factors describing composite nucleons. Numerical results show that this gauge-invariance procedure, when compared to Ohta's, leads to a much improved description of experimental data. Predictions for the new Bonn SAPHIR data for $p(\gamma,K^+)\Lambda$ are given. 
H. Haberzettl, C. Bennhold, T. Mart, and T. Feuster