Fluid dynamics far-from-equilibrium: a concrete example

In this contribution we propose a more general derivation of relativistic fluid dynamics from kinetic theory, in which the fluid is assumed to be close to an isotropic non-equilibrium state instead of an equilibrium one. We demonstrate that, for a classical gas of massless particles, it is possible to obtain a hydrodynamic theory described by equations of motion that are identical to those commonly solved in heavy ion collisions. The only difference appears in the form of the transport coefficients that enter the equations of motion. We then calculate these transport coefficients for a few choices of isotropic distribution functions and discuss their sensitivity to the underlying non-equilibrium state.