Chiral symmetry and the A 1 contribution to the nucleon-nucleon interaction

Abstract

The contribution of A 1 exchange to the nucleon-nucleon potential is studied in a broken chiral symmetric model. The A 1 is treated as a finite-width resonance in the πρ s-wave. Connections between pseudoscalar and pseudovector pion-nucleon coupling in the underlying model lagrangian are studied in detail. It is found that large terms in the NN interaction arising from πρ exchange with pseudoscalar coupling are suppressed by interference with a 1 exchange. With pseudovector coupling there is a suppression of the A 1 exchange by the so-called “seagull” terms in πρ exchange which arise from gauge invariance. The suppression becomes an exact cancellation in the limit of infinite ρ and a 1 masses and exact chiral symmetry. We found that inclusion of the a 1 decay into the πρ state strongly modifies the a 1] exchange potential, suppressing the tensor part but leaving the spin-spin part almost unchanged.