correlator within the instanton vacuum model
Bogoliubov Laboratory of Theoretical Physics, Joint Institute for Nuclear Research, 141980, Dubna, Russia
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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, w L, and transversal, w T, with respect to the axial-vector index. Within the instanton model the saturation of the anomalous w L structure is demonstrated. It is known that in the chiral limit the transversal structure w T is free from perturbative corrections. In this limit within the instanton model we calculate the transversal invariant function w T at arbitrary space-like momentum transfer q and show the absence of power corrections to this structure at large q 2. Instead there arise exponential corrections to w T at large q 2 reflecting non-local properties of the QCD vacuum. The slope of w T at zero virtuality, the QCD vacuum magnetic susceptibility of the quark condensate and its momentum dependence are estimated.
© Springer-Verlag, 2005