  The lensing magnification effect due to large-scale structure is
statistically measurable by correlation of size fluctuations in distant galaxy
images as well as by the QSO-galaxy cross-correlation. We use the halo model
formulation of Takada & Jain (2003) to compute these magnification-induced
correlations without employing the weak lensing approximation, mu=1+2kappa. Our
predictions thus include the full contribution from non-linear magnification
that is due to lensing halos. We compare the model prediction with ray-tracing
simulations and find excellent agreement over a range of angular scales
(0.'5<theta<30').
  The non-linear magnification contribution enhances the amplitude of the
magnification correlation relative to the weak lensing approximation, and the
non-linear correction is more significant on smaller angular scales and for
sources at higher redshifts. The enhancement amounts to 10-25% on arcminite
scales for the QSO-galaxy cross-correlation, even after inclusion of a
realistic model of galaxy clustering within the host halo. Therefore, it is
necessary to account for the non-linear contribution in theoretical models in
order to make an unbiased, cosmological interpretation of the precise
measurements expected from forthcoming massive surveys.
