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

Abstract

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 $\mathcal{O}(1/N_c)$-, $\mathcal{O}(m/N_c)$-, and $\mathcal{O}((m\ln m)/N_c)$-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 $1/N_c$ corrections should be reconsidered in the systematical way. The present results are consistent with those from chiral perturbation theory.

Comments: Final version accepted for publication in Phys. Lett. B. The title was changed. Small corrections were added