TRANSVERSE-MOMENTUM DISTRIBUTION IN HADRONS - WHAT CAN WE LEARN FROM QCD

We discuss some strict QCD constraints on the light-cone pi meson wave function psi(($) over right arrow k(perpendicular to)(2),x). The analysis is based on such general methods as dispersion relations, duality, and partial conservation of axial-vector current. We calculate the asymptotic behavior of the wave function (WF) at the end-point region (x --> 1 and ($) over right arrow k(perpendicular to)(2) --> infinity) by analyzing the corresponding large nth moments in transverse [($) over right arrow k(perpendicular to)(2n)]similar to n! and logitudinal[(2x - 1)(n)]similar to 1/n(2) directions. This information fixes the asymptotic behavior of the WF at large ($) over right arrow k(perpendicular to)(2) asymptotic behavior of the WF at large ($) over right arrow k perpendicular to(2) (which turns out to be the Gaussian commonly used in phenomenological analyses). We discuss one particular application of the obtained results. We calculate the nonleading ''soft'' contribution to the pion form factor at intermediate momentum transfer. We argue that, due to the specific properties of psi(($) over right arrow k(perpendicular to)(2),x), the corresponding contribution can temporarily simulate the leading twist behavior in the extent region of Q(2): 3 GeV2 less than or equal to Q(2) less than or equal to 40 GeV2, where Q(2)F(Q(2)) similar to const. Such a mechanism, if it is correct, would be an explanation of the phenomenological success of the dimensional counting rules at available, very modest energies for many different processes. We discuss some inclusive amplitudes (such as Drell-Yan and deep inelastic) where the intrinsic rr meson structure might be essential. The relation to the valence quark model is also discussed.