Properties of the SU(N_c) Yang-Mills vacuum state

Abstract

The asymptotic behaviour of the vacuum energy density, $\bar{E}(\theta )$, at $θ\ra \pm i \infty$ is found out. A new interpretation and a qualitative discussion of the $\bar{E}(\theta )$ behaviour are presented. It is emphasized that the vacuum is doubly degenerate at $\theta =\pi$, and the quark electric string can terminate on the domain wall interpolating between these two vacua. The potential of the monopole field condensing in the Yang-Mills vacuum is obtained.

17 pages, Latex, no figures; additional explanations are given in sects.1 and 3; the final version