Before revision:  Thin concentrated bands of aligned pusher particles are always unstable, while bands of aligned puller particles can either be stable (immotile particles)  or unstable (motile particles) with a growth rate which is non-monotonic in the force dipole strength.
After revision:  Thin concentrated bands of aligned pusher particles are always unstable, while bands of aligned puller particles can either be stable (immotile particles) , or unstable (motile particles) with a growth rate which is non-monotonic in the force dipole strength.