Derivation of the Effective Pion-Nucleon Lagrangian within Heavy Baryon Chiral Perturbation Theory

Abstract

We develop a method for constructing the Heavy Baryon Chiral Perturbation Theory Lagrangian (L_{HBChPT}), to a given chiral order, within HBChPT. We work within SU(2) theory, with only the pion field interacting with the nucleon. The main difficulties, which are solved, are to develop techniques for implementing charge conjugation invariance, and for taking the nucleon on shell, both within the nonrelativistic formalism. We obtain complete lists of independent terms in L_{HBChPT} through O(q^3) for off- shell nucleons. Then, eliminating equation-of-motion (eom) terms at the relativistic and nonrelativistic level (both within HBChPT), we obtain L_{HBCHPT} for on-shell nucleons, through O(q^3). The extension of the method (to obtain on-shell L_{HBChPT} within HBChPT) to higher orders is also discussed.