Chiral perturbation theory

Abstract

In the limit of vanishing up, down and strange quark masses, QCD exhibits a chiral symmetry. This symmetry is broken spontaneously to its vector subgroup, giving rise to Goldstone bosons. These acquire a small mass through the explicit chiral symmetry breaking for non-vanishing quark masses. The consequences of these broken symmetries can be investigated in a suitably tailored effective field theory called chiral pertubation theory. It admits a perturbative expansion in the external momenta and the Goldstone boson masses and can be systematically analyzed in terms of a loop expansion. The appearing ultraviolet divergences in loop diagrams can be dealt with order-by-order through the Goldstone boson contact interactions. Matter fields like the lowest-lying baryons can also included, leading to a rich and testable phenomenology of low-energy QCD.

23 pages, 3 figures, commissioned article for the Enzyclopedia of Particle Physics, typos corrected, one equation added for clarity

References in corpus (24)

• FLAG Review 2021
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• Axial structure of the nucleon
• Renormalization of relativistic baryon chiral perturbation theory and power counting
• Chiral Perturbation Theory and Baryon Properties
• Roy-Steiner-equation analysis of pion-nucleon scattering
• Chiral Perturbation Theory Beyond One Loop
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• Chiral perturbation theory
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• Extracting the chiral anomaly from gamma pi --> pi pi
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• The decay pi0 to gamma gamma to next to leading order in Chiral Perturbation Theory
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• Test of low-energy theorems for p(\vec{gamma},π^{0})p in the threshold region
• Infrared regularization of baryon chiral perturbation theory reformulated
• Neutral Pion Lifetime Measurements and the QCD Chiral Anomaly
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• The anomalous process gamma pi -> pi pi to two loops
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• Threshold neutral pion photoproduction off the tri-nucleon to O(q^4)