Pion-nucleon scattering in covariant baryon chiral perturbation theory with explicit Delta resonances

We present the results of a third order calculation of the pion-nucleon scattering amplitude in a chiral effective field theory with pions, nucleons and delta resonances as explicit degrees of freedom. we work in a manifestly lorentz invariant formulation of baryon chiral perturbation theory using dimensional regularization and the extended on-mass-shell renormalization scheme. in the delta resonance sector, the on mass-shell renormalization is realized as a complex-mass scheme. by fitting the low-energy constants of the effective lagrangian to the s- and p -partial waves a satisfactory description of the phase shifts from the analysis of the roy-steiner equations is obtained. we predict the phase shifts for the d and f waves and compare them with the results of the analysis of the george washington university group. the threshold parameters are calculated both in the delta-less and delta-full cases. based on the determined low-energy constants, we discuss the pion-nucleon sigma term. additionally, in order to determine the strangeness content of the nucleon, we calculate the octet baryon masses in the presence of decuplet resonances up to next-to-next-to-leading order in su(3) baryon chiral perturbation theory. the octet baryon sigma terms are predicted as a byproduct of this calculation.