Evidence of Instanton Effects in Hadrons from the Study of Low Eigenfunctions of the Dirac Operator

To elucidate the role in hadron structure of quark zero modes associated with instantons, the lowest eigenfunctions of the Dirac operator have been calculated in quenched QCD, full QCD, and full QCD with cooling. Eigenmodes associated with a single instanton and an instanton-anti-instanton pair were studied to understand the role of lattice artifacts for Wilson Fermions. By truncating the spectral representation of the quark propagator, we show that the rho and pion contributions to the vector and pseudoscalar correlation functions are dominated by the zero-mode contributions.