MULTIINSTANTON EFFECTS IN QCD SUM-RULES FOR THE PION

Multi-instanton contributions to QCD sum rules for the pion are invest igated within a framework which models the QCD vacuum as an instanton liquid. It is shown that, in a singular gauge, the sum of the planar d iagrams to leading order of the 1/N-c expansion provides results simil ar to those for the effective single-instanton contribution. These eff ects are also analysed in the regular gauge. Our findings confirm that at large distances the correlator functions are more adequately descr ibed in the singular gauge rather than in the regular one.