The Fundamental Nature of Low-Energy Pion-Nucleon Interactions

TL;DR

This paper reviews low-energy pion-nucleon interactions, emphasizing their connection to QCD through effective field theory, and highlights the need for improved data to advance understanding of key phenomena like the sigma term and isospin violation.

Contribution

It provides a pedagogic overview of low-energy pion-nucleon physics, connecting experimental issues with theoretical frameworks like chiral effective field theory.

Findings

Low-energy pion-nucleon scattering relates directly to QCD.

Current data limitations hinder understanding of the sigma term and isospin violation.

Effective field theory is central to interpreting low-energy interactions.

Abstract

A historical review of pion-nucleon interactions at low energy is presented, with aims toward an introductory, pedagogic approach focusing on issues germane to current research. These topics include the use of chiral effective field theory, the sigma term, qualitative understanding of low-energy phase shifts, the physics of the $\Delta$ resonance, and isospin violation. A theme is that low-energy pion-nucleon scattering is directly related to QCD via effective field theory. Another theme is that modern needs regarding the pion-nucleon sigma term and the study of isospin violation requires a better low-energy data set.