Structure and Dynamics of Disclination Loops and Lines in 3D Active Nematic Flows

Topological defects are essential to the chaotic self-stirring of active nematics, whose internally driven flows couple to orientational distortions. However, while the 2D case is well-studied, in 3D the nematic topological defects become much more complex, including curvilinear disclinations of variable winding character. To understand 3D active nematic flow dynamics, we present calculations of active hydrodynamics with nematic elasticity, together with topological analysis of data from the first experiments on bulk 3D active nematics. We show that the dominant topological excitations are a certain geometrical family of topologically neutral closed-loop disclinations, which move, deform, reconnect, and self-annihilate under the flow fields that they generate.