SYSTEMATIC 1 M EXPANSION FOR SPIN-3/2 PARTICLES IN BARYON CHIRAL PERTURBATION-THEORY/

Starting from a relativistic formulation of the pion-nucleon-delta sys tem, the most general structure of 1/M corrections for a heavy baryon chiral lagrangian including spin 3/2 resonances is given. The heavy co mponents of relativistic nucleon and delta fields are integrated out a nd their contributions to the next-to-leading order lagrangians are co nstructed explicitly. The effective theory obtained admits a systemati c expansion in terms of soft momenta, the pion mass m(pi) and the delt a-nucleon mass difference Delta. As an application, we consider neutra l pion photoproduction at threshold to third order in this small scale expansion.