  We use semi-analytic models of galaxy formation combined with high resolution
N-body simulations to make predictions for galaxy-dark matter correlations and
apply them to galaxy-galaxy lensing. We analyze cross-correlation spectra
between the dark matter and different galaxy samples selected by luminosity,
color or star formation rate. We compare the predictions to the recent
detection by SDSS. We show that the correlation amplitude and the mean
tangential shear depend strongly on the luminosity of the sample on scales
below 1 Mpc, reflecting the correlation between the galaxy luminosity and the
halo mass. The cross-correlation cannot however be used to infer the halo
profile directly because different halo masses dominate on different scales and
because not all galaxies are at the centers of the corresponding halos. We
compute the redshift evolution of the cross-correlation amplitude and compare
it to those of galaxies and dark matter. We also compute the galaxy-dark matter
correlation coefficient and show it is close to unity on scales above r > 1 Mpc
for all considered galaxy types. This would allow one to extract the bias and
the dark matter power spectrum on large scales from the galaxy and galaxy-dark
matter correlations.
