Generic Phase Diagram of Active Polar Films

We study theoretically the phase diagram of compressible active polar gels such as the actin network of eukaryotic cells. Using generalized hydrodynamics equations, we perform a linear stability analysis of the uniform states in the case of an infinite bidimensional active gel to obtain the dynamic phase diagram of active polar films. We predict, in particular, modulated flowing phases and a macroscopic phase separation at high activity. This qualitatively accounts for experimental observations of various active systems, such as actomyosin gels, microtubules and kinesins in vitro solutions, or swimming bacterial colonies.