Spontaneous chiral symmetry breaking in active fluids*

Recent experiments show that bacterial and other active suspensions in confined geometries can self-organize into persistent flow structures that exhibit spontaneously broken mirror symmetry. I will discuss how this effect can be used to realize states of collective ferro- and anti-ferromagnetic order in bacterial spin lattices. To describe actively driven solvent flows within a minimal theoretical framework, we consider generalized Navier-Stokes (GNS) equations that combine a generic linear instability mechanism with a conventional advective nonlinearity. This phenomenological model is analytically tractable and captures a number of experimental observations. Triad analysis and numerical simulations of the GNS system predict that 3D active flows can realize chiral Beltrami vector fields that support inverse energy transport from smaller to larger scales, in contrast to classical 3D turbulence.