Chiral Quark Model Explores Spontaneous Symmetry Breaking in Hadronic Physics

For over six decades, quark models have provided a fundamental framework for understanding the building blocks of matter, specifically particles known as hadrons. Alexey Nefediev from the Helmholtz-Institut für Strahlen- und Kernphysik, Universität Bonn, and colleagues demonstrate the continuing relevance of these models despite recent experimental discoveries of more complex hadronic states. This research revisits a chiral quark model, inspired by field theory, to explore how fundamental symmetries break down and influence the properties of hadrons. By providing a clear and physically intuitive picture of the strong force, described by quantum chromodynamics, this work offers valuable insights into the behaviour of matter under extreme conditions, such as the high temperatures found in the early universe.

Quark models have a rich history spanning over 60 years, consistently serving as powerful tools for investigating and predicting the behaviour of hadrons, particles governed by the strong force. Despite the emergence of new experimental data revealing hadrons that deviate from simple classifications, these models remain valuable, providing a framework for understanding the underlying structure of these particles and the strong force that binds them. This motivates continued exploration of quark model capabilities, particularly in light of increasingly complex experimental landscapes and the need to reconcile theoretical predictions with observed phenomena.

This review presents a chiral quark model, a theoretical approach inspired by quantum field theory, which provides valuable insights into various phenomena inherent in quantum chromodynamics (QCD). The model is well suited for studying the spontaneous breaking of chiral symmetry within the vacuum of the strong force, as well as its implications for the spectrum of hadrons. It also enables investigations into the restoration of chiral symmetry at elevated temperatures.

Exotic Hadrons and Chiral Symmetry Breaking

This analysis examines a collection of physics publications, primarily focused on hadron physics, quark models, lattice QCD, exotic hadrons, chiral symmetry breaking, and effective field theories. The research explores the structure and properties of hadrons, particles composed of quarks and gluons. L. Y. Glozman emerges as a prominent author, with their work central to many of the topics covered.

A. V. Nefediev and M. Denissenya frequently collaborate with Glozman, indicating a strong research partnership. Key themes include refining and extending quark models to accommodate new experimental findings, performing lattice QCD calculations to directly compute hadron properties from the fundamental theory of the strong force, investigating the existence and properties of exotic hadrons containing more than three quarks, and understanding how chiral symmetry is broken in QCD and its impact on hadron properties.

Effective field theories are also employed to simplify calculations and provide insights into hadron interactions. The research demonstrates a comprehensive approach to hadron physics, combining theoretical developments with numerical simulations. The frequent collaboration between researchers suggests a long-term research program with ongoing investigations and refinements. Review papers within the collection provide valuable overviews of the broader context of the research.

Chiral Symmetry Breaking and Hadron Spectra

Building upon a 60-year history of successful quark models, which classify hadrons as being composed of fundamental particles called quarks, the presented model addresses recent experimental discoveries revealing hadrons that do not fit neatly into this simple classification. Despite these discoveries, quark models remain central to understanding hadron properties and interactions. The model specifically focuses on how chiral symmetry, a fundamental concept in particle physics, is broken within the vacuum of the strong force and how this impacts the observed spectrum of hadrons. It provides a means to investigate the behaviour of hadrons at both normal and extremely high temperatures, offering insights into the restoration of chiral symmetry under these conditions.

The approach successfully describes mesons, particles composed of a quark and an antiquark, and can be extended to more complex multiquark states. The authors acknowledge that the model, like all theoretical frameworks, has limitations and requires ongoing refinement with new experimental data. Future research directions include exploring the model’s predictions for exotic multiquark states and further investigating the behaviour of hadrons under extreme conditions. The model represents a valuable tool for interpreting current experiments and guiding future investigations into the fundamental nature of the strong force.