  We study experimentally and theoretically the hydrodynamic coupling between
Brownian colloidal particles diffusing along a linear channel. The
quasi-one-dimensional confinement, unlike other constrained geometries, leads
to a sharply screened interaction. Consequently, particles move in concert only
when their mutual distance is smaller than the channel width, and two-body
interactions remain dominant up to high particle densities. The coupling in a
cylindrical channel is predicted to reverse sign at a certain distance, yet
this unusual effect is too small to be currently detectable.
