CHIRAL CORRECTIONS TO THE S-WAVE PION-NUCLEON SCATTERING LENGTHS

We calculate the chiral corrections to Weinberg's prediction for the S-wave piN scattering lengths up-to-and-including order O(M(pi)3) making use of heavy baryon chiral perturbation theory. For the isospin-odd scattering length a- these corrections are small and bring the prediction closer to the empirical value. In the case of the isospin-even a+ large cancellations appear so that the O(M(pi)3) result depends sensitively on certain resonance parameters which enter the calculation of the contact terms present at next-to-leading order.