Manifestly-covariant p3 calculation of nucleon Compton scattering

We compute the Compton scattering off the nucleons in the framework of manifestly covariant baryon chiral perturbation theory (BχPT). The results for observables differ substantially from the corresponding calculations in heavy-baryon chiral perturbation theory (HBχPT), most appreciably in the forward kinematics. We verify that the covariant p ³ result fulfills the forward-Compton-scattering sum rules. We also explore the effect of the Δ(1232) resonance at order p ⁴/Δ, with Δ ≈ 300 MeV, the resonance excitation energy. We find that the substantial effect of the Δ-excitation on the nucleon polarizabilities can naturally be accommodated in the manifestly covariant calculation. The article is published in the original.