Hard diffractive electroproduction, transverse momentum distribution, and QCD vacuum structure

We study the impact of the ``intrinsic'' hadron transverse momentum on the pre-asymptotic behavior of the diffractive electroproduction of a longitudinally polarized ρ meson. Surprisingly, we find the onset of the asymptotic regime in this problem to be rather low, Q²10 GeV² where power corrections due to the transverse momentum do not exceed 20% in the amplitude. This drastically contrasts with exclusive amplitudes where the asymptotics start much higher, Q²=50--100 GeV². The sources of such unexpected behavior are traced back to some general (the quark-hadron duality) as well as more silent (properties of higher dimensional vacuum condensates) features of QCD.