  Particles that are immersed in a fluid exchange momentum via the fluid, hence
their Brownian motion is correlated. By means of multiparticle-collision
dynamics simulations we study the interactions between two colloidal beads in a
sheared fluid suspension. Recently, this topic has been addressed in
experiments on colloidal particles trapped by optical tweezers in a
microfluidic device [PRL, 103, 230602 (2009)] and theoretically by means of a
Langevin model [Eur. Phys. J E, 33, 313 (2010)]. Although we neglect the
rotational degrees of freedom of the colloids, and employ a very simple
coupling between the colloids and the flow field, we can reproduce the
experimental data and partly explain why it differs from theory.
