Including the $\mathrm{\Delta }(1232)$ resonance in baryon chiral perturbation theory

Baryon chiral perturbation theory with explicit $\mathrm{\Delta }(1232)$ degrees of freedom is considered. Using the extended on-mass-shell renormalization scheme, a manifestly Lorentz-invariant effective field theory with a systematic power counting is obtained. As applications we discuss the mass of the nucleon, the pion-nucleon sigma term, and the pole of the $\mathrm{\Delta }$ propagator.