Chiral corrections to the Kroll-Ruderman theorem

We calculate the one-loop corrections to the Kroll-Ruderman low-energy theorems for charged pion photoproduction in the framework of heavy baryon chiral perturbation theory. We predict the threshold S-wave multipole E0+ to be E0+thr (γp → π+ n) = (28.2 ± 0.6) · 10−3/Mπ and E0+thr (γn → π−p) = (−32.7 ± 0.6) · 10−3/Mπ, respectively, for a fixed pion-nucleon coupling constant, gπN = 13.4. A comparison to the existing data is also given.