The relevance of pion-exchange contributions versus contact terms in the chiral effective field theory description of nucleon-nucleon scattering

TL;DR

This paper systematically analyzes the roles of pion-exchange contributions and contact terms in low partial wave nucleon-nucleon scattering within chiral effective field theory, highlighting the signature of chiral symmetry.

Contribution

It provides a detailed, systematic investigation of how chiral pion exchanges and contact interactions influence low partial wave NN scattering, clarifying the manifestation of chiral symmetry.

Findings

Chiral symmetry signatures are identifiable in lower partial waves.

Pion-exchange contributions significantly influence phase shifts.

Contact terms are less dominant in lower partial waves than previously thought.

Abstract

The standard way to demonstrate the relevance of chiral symmetry for the NN interaction is to consider higher partial waves of NN scattering which are controlled entirely by chiral pion-exchanges (since contacts vanish). However, in applications of NN-potentials to nuclear structure and reactions, the lower partial waves are the important ones, making the largest contributions. Lower partial waves are sensitive to the short-range potential, and so, when the short-range contacts were to dominate over the chiral pion-contributions in lower partial waves, then the predictions from "chiral potentials" would have little to do with chiral symmetry. To address this issue, we investigate systematically the role of the (chiral) one- and two-pion exchanges, on the one hand, and the effect of the contacts, on the other hand, in the lower partial waves of NN scattering. We are able to clearly identify the signature of chiral symmetry in lower partial waves. Our study has also a pedagogical spin-off as it demonstrates in detail how the reproduction of the lower partial-wave phase shifts comes about from the various ingredients of the theory.