Quantum chromodynamics is the gauge theory of quarks and gluons. At low energies it confines coloured fields into gauge-singlet hadrons.
In massless QCD, a quark condensate breaks to the diagonal vector subgroup. The associated Goldstone modes are the light pseudoscalar mesons.
The pion decay constant normalizes the axial current matrix element and the leading pion nonlinear-sigma-model action. It has mass dimension one in four spacetime dimensions.
A pion is one of the light pseudoscalar mesons produced by chiral symmetry breaking in quantum chromodynamics. The charge states are , and .
Articles by others on the same topic
Quantum Chromodynamics (QCD) is the theory that describes the strong interaction, one of the four fundamental forces in nature, which governs the behavior of quarks and gluons—the fundamental particles that make up protons, neutrons, and other hadrons.
Quarks, Gluon flux tubes, Strong Nuclear Force, & Quantum Chromodynamics by Physics Videos by Eugene Khutoryansky (2018)
Source. Some decent visualizations of how the field lines don't expand out like they do in electromagnetism, suggesting color confinement.