Calculation of some properties of vacuum and pi, sigma, mesons in the global color symmetry model

Based on the quark propagator derived in the instanton dilute liquid approx imation, the quark condensate <(q) over barq >, the mixed quark gluon conde nsate g(a)< qG(muv)sigma (muv)q > the four-quark condensate <(q) over bar G ammaq (q) over bar Gammaq > and tensor, pion vacuum susceptibilities have b een calculated at the mean-field level in a nonperturbative QCD model. The numerical results are compatible with the values obtained within other nonp erturbative approaches. The calculated masses and decay constants of pi and sigma mesons are close to the experimental values. These results show that the instanton medium might be a good approximation of the QCD vacuum.