The quark-confinement conjecture for the Yang–Mills theory

Let $G$ be the gauge group and let the nontrivial Yang–Mills theory on Minkowskian spacetime $\mathbf{R}^{1,3}$ be the theory whose existence and quantization are asserted by the Yang–Mills mass gap conjecture. Quark-confinement conjecture. This nontrivial Yang–Mills theory has quark confinement.

Quark confinement is the property that physical particle states corresponding to quarks are not observed freely; in the $\operatorname{SU}(3)$ theory, the physical particle states corresponding to protons, neutrons, and pions are $\operatorname{SU}(3)$-invariant. The source describes the four-dimensional $\operatorname{SU}(3)$ case as unsolved, while relating confinement to Wilson's area law.