Coulomb drag of viscous electron fluids: Drag viscosity and negative drag conductivity

We show that Coulomb drag in bilayer systems the regime of electron hydrodynamics leads to additional viscosity terms hydrodynamic equations, drag, and drag-Hall viscosities, besides well-known kinematic Hall viscosities. These arise from a change stress tensor due interlayer interactions. All four are tunable by varying applied magnetic field densities two layers. At certain ratios between layers, dramatically changes longitudinal transport resulting negative conductivity.