Sriram Ramaswamy: Superdiffusion and antidiffusion in an aligned active suspension

Sriram Ramaswamy, Indian Institute of Science, Bengaluru

Tiny self-propelled particles in a fluid display complex collective behavior because the flows they create as they swim act back on their movement. We show theoretically that simply favouring motion along one axis in such a system can radically alter its state of organization, yielding spreading faster than diffusion in dilute suspensions, as we confirm in particle-based simulations. At higher concentrations we predict a hitherto unknown mechanism for clustering through active flow. We suggest experimental settings in which to realise these effects and test our predictions. This work, done with LP Dadhichi, SK Sahoo, and K Vijay Kumar, can be found at arXiv:2510.00740 and Phys. Rev. Lett. 136, 128302 (2026).