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 eme rge from QCD for these states in the combined large-N-c and heavy-quark lim its. The effective theory is based on perturbations about this limit; a pow er-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 s trong interaction scale). We derive the effective Hamiltonian for strong in teractions at next-to-leading order. The next-to-leading-order effective Ha miltonian depends on only two parameters beyond the known masses of the nuc leon 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.