While statistical mechanics provides us with powerful tools to analyze systems in equi- librium, most of the world around us is far from this idealized situation. Near thermal equilibrium, one can use hydrodynamics to analyze the dynamics of small, long wavelength fluctuations. But to understand far from equilibrium physics is a notoriously challenging problem. An interesting yet potentially tractable class of non-equilibrium configurations is represented by steady state flows. Examples of steady state flows are an electric current in a conductor driven by an external electric field or a heat current driven by a temperature gradient. These configurations can be described by a time-independent configuration, but neither of these corresponds to equilibrium. In both cases entropy is produced constantly and needs to be absorbed by the battery or heat bath in order to maintain the steady flow.
In a recent paper H. Chang, A. Karch and A. Yarom have constructed an ansatz which describes a particular type of such a steady state configuration. The particular solution which has been constructed is such that, in conformal theories, the properties of the steady-state heat current is independent of the parameters of the theory and is, in this sense, universal. Various indications as to the validity of this ansatz have been given, but it has not been rigorously proven or tested very robustly.