CHIRAL QCD VACUUM ENERGY DENSITY IN THE ZERO MODES ENHANCEMENT QUANTUM MODEL

Using the effective potential approach for composite operators we have formulated the quantum model of the QCD vacuum. It is based on the existence and importance of the nonperturbative q-4-type dynamical, topologically nontrivial excitations of the gluon field configurations (due to self-interaction of the massless gluons only). The QCD vacuum is found to be stable since the vacuum energy density has no imaginary part. The Yang–Mills (YM) part of the vacuum energy density is always negative and depends on a finite scale at which nonperturbative effects become important. The quark part of the vacuum energy density depends in addition on the constant of integration of the corresponding Schwinger–Dyson equation. The value of the above-mentioned scale is determined from the bounds for the pion decay constant in the chiral limit. Our value for the chiral QCD vacuum energy density is one order of magnitude bigger than the instanton based models can provide while a fair agreement with recent phenomenological and lattice results for the chiral condensate is obtained.