Scattering and nonlinear bound states of hydrodynamically coupled particles in a narrow channel.

We model a pair of hydrodynamically interacting particles confined in a channel with thin rectangular cross section. We find that the particles have a finite region of attraction, which arises from the screening of dipolar hydrodynamic interactions by the side walls. Outside this region, the two particles break apart and scatter; inside, they oscillate together as an effectively free quasiparticle. We demonstrate that modulation of channel geometry provides a means to irreversibly manipulate bound pairs.