  Understanding how chiral active particles -- which self-propel and
self-rotate -- interact with each other is crucial to uncover how chiral active
matter self-organizes into dynamic structures and patterns. Long-range
fluctuation-induced (FI) forces in nonequilibrium steady states of active
matter systems can be considerably strong and govern structure formation in
interplay with other interactions. However, the impact of chirality on FI
forces is not understood to date. We study effective forces between intruders
immersed in chiral active fluids with tunable chirality and find that the
influence of chirality on the FI force nontrivially depends on the elongation
of active particles. By increasing the ratio between self-rotation and
self-propulsion, the FI force monotonically decreases for fully circular active
objects, as the active bath structure gradually changes from rotating flocks
and vortices to localized spinners. Contrarily, a nonmonotonic behavior is
observed upon increasing the chirality of rodlike active objects: There exists
an optimal chiral angle which maximizes the magnitude and range of the FI
interaction. We obtain the phase diagram of transition between attractive and
repulsive forces in the space of chirality, propulsion, and separation between
intruders. By measuring the collision statistics between active particles and
intruders at different chirality and separation, we establish a direct link
between the FI force and the average collision number and demonstrate how the
balance of collisions around the intruders varies with chirality and
separation. Our results provide new insights into an interplay between
activity, chirality, and self assembly.
