  In a system of colloidal inclusions suspended in a thermalized bath of
smaller particles, the bath engenders an attractive force between the
inclusions, arising mainly from entropic origins, known as the depletion force.
In the case of active bath particles, the nature of the bath-mediated force
changes dramatically from an attractive to a repulsive one, as the strength of
particle activity is increased. We study such bath-mediated effective
interactions between colloidal inclusions in a bath of self-propelled Brownian
particles, being confined in a narrow planar channel. Confinement is found to
have a strong effect on the interaction between colloidal particles, however,
this mainly depends on the colloidal orientation inside the channel. Effect of
the confinement on the interaction of colloidal disk is controlled by the
layering of active particles on the surface boundaries. This can emerge as a
competitive factor, involving the tendencies of the channel walls and the
colloidal inclusions in accumulating the active particles in their own
proximity.
