A proposal for the Yang–Mills vacuum and mass gap

I examine a set of Feynman rules, and the resulting effective action, that were proposed in order to incorporate the constraint of Gauss’s law in the perturbation expansion of gauge field theories. A set of solutions for the Lagrangian and Hamiltonian equations of motion in Minkowski space-time, as well as their stability, are investigated. A discussion of the Euclidean action, confinement, and the strong-CP problem is also included. The properties and symmetries of the perturbative and the confining vacuum are explored, as well as the possible transitions between them, and the relations with phenomenological models of the strong interactions.