Vector-meson electroproduction at small Bjorken-x and generalized parton distributions

We analyze electroproduction of light vector mesons ( V = rho, phi) at small Bjorken-x in an approach that includes the gluonic generalized parton distributions and a partonic subprocess, gamma g -> (q (q) over bar )g, q (q) over bar -> V. The subprocess is calculated to lowest order of perturbative QCD taking into account the transverse momenta of the quark and antiquark as well as Sudakov suppressions. Our approach allows us to investigate the transition amplitudes for all kinds of polarized virtual photons and polarized vector mesons. Modeling the generalized parton distributions through double distributions and using simple Gaussian wavefunctions for the vector mesons, we compute the longitudinal and transverse cross sections at large photon virtualities as well as the spin-density matrix elements for the vector mesons. Our results are in fair agreement with the findings of recent experiments performed at HERA.