Hydrodynamics of active fluids

In this talk, I will discuss some of our recent efforts to derive effective descriptions of the collective dynamics of active fluids, a broad class of systems for which local energy injection is converted into directed motion. Such systems evolve far from equilibrium, which precludes the standard formulation of hydrodynamic theories and the linear response relationships that tie them to their microscopic constituents, as well as making it difficult to anticipate the scale of their fluctuations. We have developed a framework to deduce effective hydrodynamic descriptions for locally conserved quantities when time reversal symmetry is broken, to generalize linear response relations around nonequilibrium steady-states, and evaluate fluctuations of time-integrated quantities. This framework relies on the mathematics of large deviation theory and stochastic thermodynamics, as well as numerical techniques that afford means of determining rare fluctuations in driven systems. I will highlight some specific examples in scalar and chiral active matter for which we have studied the effect of Hall-like transport coefficients of tracer dynamics and predicted the emergence of propagating boundary modes.

Speaker: David Limmer, UC Berkeley