NEUTRAL PION-PHOTOPRODUCTION OFF NUCLEONS REVISITED

We investigate threshold pion photoproduction in the framework of heav y baryon chiral perturbation theory. We give the expansion of the elec tric dipole amplitude E(0+) to three orders in mu, the ratio of the pi on to nucleon mass, and show that it is slowly converging. We argue th at this observable is not a good testing ground for the chiral dynamic s of QCD. In contrast, we exhibit new and fastly converging low-energy theorems in the P-waves which should be used to constrain the data an alysis. We also discuss the importance of polarization observables to accurately pin down certain multipoles and give predictions for the re action gamma n --> pi(0)n.