Hydrodynamic origins of odd viscosity in spinner monolayers

Breaking parity and time-reversal in fluids allows to couple deformations to orthogonal stresses.  This phenomenon translates into odd continuum material constants such as Hall viscosity. 

While the continuum limit is well understood, in real systems odd viscosity arises from  microscopic interactions between fluid constituents. 

We combine  simulations and analytical calculations of rotating particles in Stokes flow to show how  odd responses can emerge  from  viscous hydrodynamic interactions in spinner monolayers.