Absence of shadowing in Drell-Yan production at finite transverse momentum exchange

Within a perturbative scalar QED model recently considered by Brodsky et al., we study how leading-twist Coulomb rescatterings affect the Drell-Yan cross section at small x=xtarget, and compare to the case of deep inelastic scattering at small xB. We show that in the range where the transverse momentum transferred to the target is large compared to its minimal value ~O(x), Coulomb rescatterings affect the DIS cross section but not the Drell-Yan production rate. This illustrates that the leading-twist parton distribution functions become nonuniversal when cross sections which are differential in target-related particles are considered.