Calculation of the Vacuum Energy Density and Gluon Condensate within Zero Modes Enhancement Model of the QCD Vacuum

The nonperturbative vacuum structure which emerges from the zero modes enhancement (ZME) model of the true QCD vacuum, appears to be well suited to describe quark confinement, dynamical chiral symmetry breaking (DCSB), current-effective (dynamical)-constituent, as well as constituent-valence quark transformations, the Okubo-Zweig-Iizuka (OZI) rule, dimensional transmutation, etc. It is based on the solution to the Schwinger-Dyson (SD) equation for the quark propagator in the infrared (IR) domain. The importance of the instanton-type fluctuations in the true QCD vacuum for the ZME model is also discussed. This allows to calculate new, more realistic values for the vacuum energy density (apart from the sign, by definition, the bag constant) and the gluon condensate. Our numerical results for the gluon condensate for different numbers of quark flavor $N_f$ are 2-3 times lager than it is estimated in the QCD sum rules approach. This is in good agreement with recent phenomenological estimates of this quantity.