Predictions of chiral perturbation theory for Compton scattering off protons

We compute the Compton scattering off the nucleons in the framework of manifestly covariant baryon chiral perturbation theory (B$\chi$PT). The results for observables differ substantially from the corresponding calculations in heavy-baryon chiral perturbation theory (HB$\chi$PT), 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 $\Delta$(1232) resonance. We find that the substantial effect of the $\Delta$-excitation on the nucleon polarizabilities can naturally be accommodated in the manifestly covariant calculation.