Including the $\Delta(1232)$ resonance in baryon chiral perturbation   theory
  Baryon chiral perturbation theory with explicit $\Delta(1232)$ 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 $\Delta$ propagator. 
C. Hacker, N. Wies, J. Gegelia, and S. Scherer