  The transition form factor, decay width and charge form factor of pion are
calculated within the model of induced nonlocal quark currents based on the
assumption that the nonperturbative QCD vacuum can be characterized by a
homogeneous (anti-)self-dual gluon field. It is shown that the interaction of
the quark spin with the vacuum gluon field, being responsible in the model for
the chiral symmetry breaking and the spectrum of light mesons, can also play
the decisive role in forming the transition form factor and two-photon decay
width. Asymptotic behavior of quark loops in the presence of the background
gluon field for large momentum transfer is discussed.
