Simulations of bulk and topologically constrained active matter

Active nematics are liquid crystals whose constituent particles transduce energy into motion. The ordered nematic state is unstable to the proliferation of topological defects, which undergo birth, streaming dynamics, and annihilation to yield a seemingly chaotic dynamical steady-state. I will describe several types of computational models for active nematics motivated by experiments at Brandeis in which microtubule bundles driven by ATP-powered motor proteins, and a few surprising things we have learned about the behaviors of active nematics in bulk and under confinement. These include heretofore unknown broken-symmetry phases in which the topological defects themselves undergo orientational ordering, renormalization of elastic moduli by activity, and a remarkable insensitivity to topological constraints even under high confinement.