Vacuum energy density of chiral QCD 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 non-perturbative q−4-type dynamical, topologically nontrivial excitations of the gluon field configurations. The QCD vacuum is found stable since the vacuum energy density has no imaginary part. We have also proposed a method how to determine finite (but always negative) the non-perturbative Yang-Mills (YM) vacuum energy density. It becomes dependent only on a scale at which non-perturbative 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 by implementing physically well-motivated scale-setting scheme.