Viscosity and dissipative hydrodynamics from effective field theory

Understand

With the goal of deriving dissipative hydrodynamics from an action, we study classical actions for open systems, which follow from the generic structure of effective actions in the Schwinger-Keldysh Closed-Time-Path formalism with two time axes and a doubling of degrees of freedom.

• The central structural feature of such effective actions is the coupling between degrees of freedom on the two time axes.
• This reflects the fact that from an effective field theory point of view, dissipation is the loss of energy of the low-energy hydrodynamical degrees of freedom to the integrated-out, UV degrees of freedom of the environment.
• The dynamics of only the hydrodynamical modes may therefore not posses a conserved stress-energy tensor.