$Δ(1232)$ Contribution in the $π$-photoproduction on Nucleons in Covariant Chiral Perturbation Theory

Abstract: We study the effects of the $\Delta$(1232) resonance as an effective degree of freedom for charged and neutral pion photo-production on nucleons. Different observables have been calculated for these processes by using relativistic chiral perturbation theory up to $\mathcal{O}(p^3)$ in the $ \delta$ counting, thus, including pion loops. We compare our model with a large database containing the available experimental data and constrain some unknown low energy constants.