Thermodynamic equilibrium as a symmetry of the Schwinger-Keldysh action
Thermodynamic equilibrium as a symmetry of the Schwinger-Keldysh action
Extended quantum systems can be theoretically described in terms of the Schwinger-Keldysh functional integral formalism, whose action conveniently describes both dynamical and static properties. We show here that in thermal equilibrium, defined by the validity of fluctuation-dissipation relations, the action of a quantum system is invariant under a certain symmetry …