Effective theory of the Delta(1232) in Compton scattering off the nucleon

Abstract

We formulate a new power-counting scheme for a chiral effective field theory of nucleons, pions, and Deltas. This extends chiral perturbation theory into the Delta-resonance region. We calculate nucleon Compton scattering up to next-to-leading order in this theory. The resultant description of existing $\gamma$p cross section data is very good for photon energies up to about 300 MeV. We also find reasonable numbers for the spin-independent polarizabilities ${\alpha }_p$ and ${\beta }_p$.

Comments: 29 pp, 9 figs. Minor revisions. To be published in PRC