Physics Colloquium 

Odd Viscosity in Active Matter

Tomer Markovich
Postdoctoral Fellow
Center for Theoretical Biological Physics
Rice University
Houston, Texas
Abstract 

Active materials are composed of many components that convert energy from the environment into directed mechanical motion, thus locally breaking time reversal symmetry (TRS). Examples of active materials are abundant, from living systems such as bacteria to colloidal rollers. A striking phenomenon of breaking TRS is the possible appearance of odd viscosity. Onsager reciprocal relations require that when TRS holds the viscosity tensor is symmetric for exchanging its first and last pair of indices. However, when TRS is broken, Onsager relations predict an odd viscosity that is both odd under TRS and under the change of indices. Such odd viscosity is non-dissipative and should thus be derivable from a Hamiltonian theory. Active materials innately break TRS, which led to recent studies of odd viscosity in 2D active materials. In this talk I will present a microscopic Hamiltonian theory for odd viscosity, valid also in 3D. Our theory give rise to intriguing 3D effects such as the breakdown of Bernoulli’s principle and propagation of bulk waves. We further predict that odd viscosity should emerge in actomyosin gels and bacterial suspensions. Finally, I will present recent results in which direct coarse-graining of the kinetic energy leads to non-reciprocal coupling between longitudinal and transverse velocities, disobeying Onsager relations.