Quantum chromodynamics

Quantum chromodynamics (QCD) is the physical theory describing one of the fundamental forces, the strong interaction. Because of its special property called asymptotic freedom, it was first proposed in the early 1970s by David Politzer and by Frank Wilczek and David Gross as a theory to understand the structure of protons, neutrons, and similar particles. It uses quantum field theory to describe the interaction of quarks and gluons. For their work in quantum chromodynamics, Gross, Wilczek, and Politzer were awarded the 2004 Nobel Prize in Physics.

According to this theory, the character of the strong interaction is determined by a special symmetry between the color charges of the quarks. This symmetry is known as the SU(3) gauge group, and the quarks transform under this group as SU(3) triplet Dirac fields. Although the perturbative expansions were important for development of QCD, QCD also predicts many non-perturbative effects such as confinement, fermion condensates and instantons.

Quantum chromodynamics is an important part of the Standard Model of particle physics. The name "chromodynamics" comes from the Greek word "chroma" Χρώμα (color). This name is relevant because the charge of the quarks is usually referred to as "color" although it is unrelated to the visual perception of color.

A particular approach to QCD, namely the lattice models, has enabled the researchers to obtain some theoretical results and quantities that were previously uncalculable.

QCD has a confining phase and a deconfining phase.

See also

• Gauge theory
• Quantum gauge theory
• BRST
• Faddeev-Popov ghost
• Strong interaction
• QCD lattice model
• Fermion condensate
• strong CP problem
• 1/N expansion
• Quantum field theory