VAV correlator within the instanton vacuum model

The correlator of vector and non-singlet axial-vector currents in the external electromagnetic field is calculated within the instanton liquid model of the QCD vacuum. In general the correlator has two Lorentz structures: longitudinal, wL, and transversal, wT, with respect to the axial-vector index. Within the instanton model the saturation of the anomalous wL structure is demonstrated. It is known that in the chiral limit the transversal structure wT is free from perturbative corrections. In this limit within the instanton model we calculate the transversal invariant function wT at arbitrary space-like momentum transfer q and show the absence of power corrections to this structure at large q2. Instead there arise exponential corrections to wT at large q2 reflecting non-local properties of the QCD vacuum. The slope of wT at zero virtuality, the QCD vacuum magnetic susceptibility of the quark condensate and its momentum dependence are estimated. (orig.)