Activity Unmasks Chirality in Liquid-Crystalline Matter

Active matter theories naturally describe the mechanics of living systems. As biological matter is overwhelmingly chiral, an understanding of the implications of chirality for the mechanics and statistical mechanics of active materials is a priority. This article examines active, chiral materials from a liquid-crystal physicist's point of view, extracting general features of broken-symmetry-ordered phases of such systems without reference to microscopic details. Crucially, this demonstrates that activity allows chirality to affect the hydrodynamics of broken-symmetry phases in contrast to passive liquid crystals, in which chirality induces the formation of a range of spatially periodic structures whose large-scale mechanics have no signatures of broken parity symmetry. In active systems, chirality leads to the formation of phases that break time translation symmetry, which is impossible in equilibrium, and the existence of new kinds of elastic force densities in translation symmetry-broken states.