Excited heavy baryons and their symmetries II: Effective theory

We develop an effective theory for heavy baryons and their excited states. The approach is based on the contracted O(8) symmetry recently shown to emerge from QCD for these states in the combined large-N-c and heavy-quark limits. The effective theory is based on perturbations about this limit; a power-counting scheme is developed in which the small parameter is lambda (1/2) where lambda similar to 1/Nc, Lambda /m(Q) (with Lambda being a typical strong interaction scale). We derive the effective Hamiltonian for strong interactions at next-to-leading order. The next-to-leading-order effective Hamiltonian depends on only two parameters beyond the known masses of the nucleon and heavy meson. We also show that the effective operators for certain electroweak transitions can be obtained with no unknown parameters at next-to-leading order. (C) 2001 Elsevier Science B.V. All rights reserved.