Yang–Mills theory
Unsolved problem in physics
Yang–Mills theory and the mass gap. Quantum particles described by the theory have mass but the classical waves of the field travel at the speed of light.
| Quantum field theory | 
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| History | 
Yang–Mills theory is a quantum field theory for nuclear binding devised by Chen Ning Yang and Robert Mills in 1953, as well as a generic term for the class of similar theories. The Yang–Mills theory is a gauge theory based on a special unitary group SU(n), or more generally any compact Lie group. A Yang–Mills theory seeks to describe the behavior of elementary particles using these non-abelian Lie groups and is at the core of the unification of the electromagnetic force and weak forces (i.e. U(1) × SU(2)) as well as quantum chromodynamics, the theory of the strong force (based on SU(3)). Thus it forms the basis of the understanding of the Standard Model of particle physics.