Meson-loop contributions to the quark condensate from the instanton vacuum

We investigate the quark condensate of the QCD vacuum within the instanton vacuum model. We calculate the meson-loop contributions to the dynamical quark mass and quark condensate to O(1/Nc)-, O(m/Nc)-, and O((mlnm)/Nc)-order corrections. We find that the meson (especially pion) loops provide substantial contributions to the dynamical quark mass and as a result to the quark condensate. The results indicate that the 1/Nc corrections should be reconsidered in the systematical way. The present results are consistent with those from chiral perturbation theory.