Threshold pion electro- and photoproduction off nucleons in covariant chiral perturbation theory

Pion electro- and photoproduction off the nucleon close to threshold is studied in covariant baryon chiral perturbation theory at O(p3) in the extended-on-mass-shell scheme, with the explicit inclusion of the Δ(1232) resonance. The relevant low energy constants are fixed by fitting the available experimental data with the theoretical model. The inclusion of the Δ resonance as an explicit degree of freedom substantially improves the agreement with data and the convergence of the model.