Testing nonperturbative Ansätze for the QCD field strength correlator

A test for the Gaussian and exponential Ansätze for the nonperturbative parts of the coefficient functions, Dnonpert. and D1nonpert., which parametrize the gauge-invariant bilocal correlator of the field strength tensors in the stochastic vacuum model of QCD, is proposed. It is based on the evaluation of the heavy-quark condensate within this model by making use of the world-line formalism and equating the obtained result to the one following directly from the QCD Lagrangian. This yields a certain relation between Dnonpert.(0) and D1nonpert.(0), which is further compared with an analogous relation between these quantities known from the existing lattice data. Such a comparison leads to the conclusion that at the distances smaller than the correlation length of the vacuum, Gaussian Ansatz is more suitable than the exponential one.