Effect of concentration fluctuations in Active Polar fluids.

Active Polar Fluids (APF) are a system consisting of head-tail asymmetric self-propelled particles (SPPs) suspended in a fluid medium. These complex active fluids show spectacular collective behavior spanning subcellular scales to oceanic scales such as the cytoskeleton, bacterial suspensions, fish schools, e.t.c. The flocking or the ordered state where all the particles move in a common direction is not always stable to small perturbations. It can destabilize into a disordered state to form complex spatiotemporal patterns. The earlier works studied such instabilities in the Stokesian regime or in the case where concentration is assumed to be homogeneous. In our work, we study the effect of fluctuations in the concentration of "extensile" or "pusher" like polar SPPs at small Reynold's number (Re