Hydrodynamic theory of an electron gas

The generalized hydrodynamic theory, which does not require assumption of a local equilibrium, is derived in the long-wave limit of a kinetic equation. In contrast to the Bloch hydrodynamics, the theory is applicable to a collisionless electron gas and correctly describes the plasmon dispersion. In a low-frequency (collision dominated) limit, Navier-Stokes hydrodynamics is recovered. In the linear approximation, the generalized hydrodynamics becomes equivalent to phenomenological theory of highly viscous fluids.