Self Propelled Rods: Insights and Perspectives for Active Matter
A wide range of experimental systems including gliding, swarming and swimming bacteria, in vitro motility assays as well as shaken granular media are commonly described as self propelled rods. Large ensembles of those entities display a large variety of self organized, collective phenomena, including formation of moving polar clusters, polar and nematic dynamic bands, mobility induced phase separation, topological defects and mesoscale turbulence, among others. Here, we give a brief survey of experimental observations and review the theoretical description of self propelled rods. Our focus is on the emergent pattern formation of ensembles of dry self propelled rods governed by short ranged, contact mediated interactions and their wet counterparts that are also subject to long ranged hydrodynamic flows. Altogether, self propelled rods provide an overarching theme covering many aspects of active matter containing well explored limiting cases. Their collective behavior not only bridges the well studied regimes of polar self propelled particles and active nematics, and includes active phase separation, but also reveals a rich variety of new patterns.