Off-Shell Photon Light-Cone Transverse Wavefunction at Leading Twist

The explicit expression of the transverse photon wavefunction Ф_γ⊥(u,P²) at the leading twist with the on-shell and the off-shell momenta are calculated in the effective low-energy theory derived from the instanton vacuum of QCD, where both the space-like region as well as the time-like one of the momenta for the virtual photons are investigated. In addition, the problem about the consistency between the two different definitions of the transverse photon wavefunction with chiral-odd Dirac structure, σ_μv, has been considered, and proven to be true at the leading order by means of the sum rule method. A brief discussion of the dependence of the transverse light-cone photon wavefunction Ф_γ⊥(u,P²) nd its coupling, F_γ^⊥(u,P²) to the corresponding quark--antiquark current with respect to P², and that about the end-point behaviour of the transverse photon wavefunction is given.