The gauge invariant quark correlator in QCD sum rules and lattice QCD
  Taking the gauge invariant quark correlator as an example, in this work we perform a direct comparison of lattice QCD simulations with the QCD sum rule approach. The quark correlator is first investigated in the framework of QCD sum rules and the correlation length of the quark field is calculated. Comparing the phenomenological part of the sum rule with previous measurements of the quark correlator on the lattice, we are able to obtain an independent result for the correlation length. From a fit of the lattice data to the operator product expansion, the quark condensate and the mixed quark-gluon condensate can be extracted. 
H.G. Dosch, M. Eidemuller, M. Jamin, E. Meggiolaro