P. Wilhelm, H. Arenhovel, C. Giusti, F.D. Pacati
Z. Phys. A359 (1997) 467. nucl-th/9702031
The paper is concerned about the proper treatment of the Delta
propagator. Fig. 1 distinguishes between time ordered diagrams, I the
Delta is excited AFTER the photon is absorbed, II the Delta is excited
BEFORE the photon is absorbed.
In the static approximation these two diagrams are the same.
The calculations have been done for the (gamma,pp) reactions and show
notieceable differences even at excitation energies of 150 MeV.