The effect of off-diagonal parton distributions in diffractive vector meson electroproduction

We present a simple physical description of the off-diagonal gluon distribution g (x,x^\prime,Q^2) and splitting function P_{gg}(x,x^\prime) which enter the amplitude for diffractive vector meson production. We study the off-diagonal effects both on the evolution in Q^2 and on the input distribution. We predict the ratio $R$ of the off-diagonal to the diagonal gluon density, x^\prime g(x,x^\prime,Q^2)/xg(x, Q^2), as a function of the kinematic variables.