Microscopic derivation of pion-nucleon and pion-Delta scattering lengths

Abstract

A general expression for the $\pi -N$ and $\pi -\Delta$ scattering lengths is derived in the framework of a microscopic calculation. Annihilation, negative energy wave-functions and spontaneous chiral symmetry are included consistently. The point-like limit is used to calculate the scattering lengths.

Comments: Clarified version of the preprint. 1 elsart manuscript, 2 eps figures