A tale of twisting columns

We formulate the hydrodynamics of active columnar phases, with two-dimensional translational order in the plane perpendicular to the columns and no elastic restoring force for relative sliding of the columns. Our predictions include: spontaneous chiral symmetry breaking through a helical instability of the columns; a spinning state of the helically buckled columns; and material transport along the columns through a viscous Archimedean screw mechanism if the columns are polar, i.e., up-down asymmetric. We further show that the polar phase provides a natural experimental setting to realise the odd elastic effects predicted for 2D solids.