Structure of large Nc cancellations in baryon chiral perturbation theory

We show how to compute loop graphs in heavy baryon chiral perturbation theory including the full functional dependence on the ratio of the Δ-nucleon mass difference to the pion mass, while at the same time automatically incorporating the 1/Nc cancellations that follow from the large-Nc spin-flavor symmetry of baryons in QCD. The one-loop renormalization of the baryon axial vector current is studied to demonstrate the procedure. A new cancellation is identified in the one-loop contribution to the baryon axial vector current. We show that loop corrections to the axial vector currents are exceptionally sensitive to deviations of the ratios of baryon-pion axial vector couplings from SU(6) values. ©2000 The American Physical Society.

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