Spatial intensity correlations between waves transmitted through random media
are analyzed within the framework of the random matrix theory of transport.
Assuming that the statistical distribution of transfer matrices is isotropic,
we found that the spatial correlation function can be expressed as the sum of
three terms, with distinctive spatial dependences. This result coincides with
the one obtained in the diffusive regime from perturbative calculations, but
holds all the way from quasi-ballistic transport to localization. While
correlations are positive in the diffusive regime, we predict a transition to
negative correlations as the length of the system decreases.Comment: 10 pages, 3 figures. Submitted to Physical Review Letter