Chiral symmetry and its breaking

TL;DR

This paper provides a pedagogical overview of chiral symmetry in strong interactions, emphasizing its approximate nature, spontaneous breaking in QCD, and the dual role of the chiral pion as a Goldstone boson and a hadron state.

Contribution

It offers a clear, pedagogical explanation of chiral symmetry and its spontaneous breaking in QCD, highlighting the dual nature of the pion.

Findings

Chiral symmetry is an approximate symmetry of strong interactions.

Spontaneous breaking of chiral symmetry occurs in the QCD vacuum.

The pion acts as both a Goldstone boson and a pseudoscalar meson.

Abstract

In addition to fundamental symmetries playing a crucial role for establishing the Standard Model of fundamental interactions, approximate symmetries provide essential insight into the respective phenomena and shed light on the underlying physics. Here we give a brief pedagogical introduction to chiral symmetry as an approximate but still rather accurate symmetry of strong interactions and its spontaneous breaking in the vacuum of Quantum Chromodynamics. Special attention is paid to a microscopic picture of this phenomenon and understanding a dual nature of the chiral pion that is the Goldstone boson related to spontaneous breaking of chiral symmetry and the lowest pseudoscalar quark-antiquark state in the spectrum of hadrons simultaneously.