Nothing anomalous about two-loop heavy baryon chiral perturbation theory: Consistency with the low energy theorem for spin-dependent Compton scattering - art. no. 017503

The leading order contributions of processes involving anomalous pion-photo n vertices to forward spin-dependent Compton scattering from nucleons are c onsidered in heavy baryon chiral perturbation theory. These all involve the exchange of three pions between one or two photons and the nucleon, and he nce are two-loop processes. We find that the sum of these processes vanishe s in the manner predicted by the low energy theorem of Low, Gell-Mann and G oldberger as the photon energy goes to zero. This provides the first consis tency test of two-loop heavy baryon chiral perturbation theory.