OFF-SHELL PHOTON LONGITUDINAL LIGHT-CONE WAVE FUNCTION AT LEADING TWIST

The leading twist longitudinal virtual photon light-cone wave function, ϕγ‖(u, P2), is calculated within the framework of the low-energy effective theory arising from the instanton model of QCD vacuum. Corresponding to the non-perturbative effects at low-energy scale, a suitable regularization scale T is fixed by analysing the differential behavior of the photon wave function on the internal transverse momentum cut-off in the light-cone frame. The coupling constant, Fγ(P2), of the quark-antiquark vector current to the virtual photon state is also obtained by imposing the normalization condition. The feature of the obtained photon wave function has been discussed at the end as well as the coupling constant.