Energy Dependence of the Delta Resonance: Chiral Dynamics in Action

TL;DR

This paper explores how chiral dynamics influence the energy dependence of the Delta resonance in pion-nucleon scattering, linking low energy QCD theorems with experimental observations.

Contribution

It demonstrates the connection between chiral symmetry breaking in QCD and the energy dependence of the Delta resonance, supported by experimental tests of chiral perturbation theory.

Findings

The shape of the Delta resonance is affected by both p wave and s wave interactions.

Chiral symmetry breaking explains the small s wave interaction.

Experimental tests support chiral perturbation theory predictions.

Abstract

There is an important connection between the low energy theorems of QCD and the energy dependence of the Delta resonance in pi-N scattering, as well as the closely related gamma^{*} N -> pi N reaction. The resonance shape is due not only to the strong pi-N interaction in the p wave but the small interaction in the s wave; the latter is due to spontaneous chiral symmetry breaking in QCD (i.e. the Nambu-Goldstone nature of the pion). A brief overview of experimental tests of chiral perturbation theory and chiral based models is presented