Chiral symmetry and the near threshold pion-induced 2π production on the nucleon: (I). General formalism

Abstract The exclusive πN → ππN reaction around the Δ-isobar region provides an excellent testing ground of chiral symmetry. As a first step, a diagrammatical approach to the π − p → π + π − n reaction is formulated based on Weinberg's chiral lagrangian. Tested are the role of various dynamical elements, particularly the significance of nonlinear contributions in the pion field as a signature of chiral symmetry.