  We use a continuum model to report on the behavior of a dilute suspension of
chiral swimmers subject to externally imposed shear in a planar channel.
Swimmer orientation in response to the imposed shear can be characterized by
two distinct phases of behavior, corresponding to unimodal or bimodal
distribution functions for swimmer orientation along the channel. These phases
indicate the occurrence (or not) of a population splitting phenomenon changing
the swimming direction of a macroscopic fraction of active particles to the
exact opposite of that dictated by the imposed flow. We present a detailed
quantitative analysis elucidating the complexities added to the population
splitting behavior of swimmers when they are chiral. In particular, the
transition from unimodal to bimodal and vice versa are shown to display a
re-entrant behavior across the parameter space spanned by varying the chiral
angular speed. We also present the notable effects of particle aspect ratio and
self-propulsion speed on system phase behavior and discuss potential
implications of our results in applications such as swimmer separation/sorting.
