Pre-equilibrium effects on the applicability of relativistic viscous hydrodynamics

In order to preserve causality in relativistic viscous hydrodynamics simulations of heavy-ion collisions, it has been recently show that a pre-equilibrium free streaming stage can play a crucial role. Freestream is an open-source Python package from the Duke-QCD group which implements the pre-equilibrium free streaming process for heavy-ion collisions. Freestream provides input for hydrodynamics codes such as the energy density, relative flow velocity, shear-stress tensor, and bulk pressure. Here we couple Freestream code together with the smoothed particle hydrodynamic (SPH) code v-USPhydro in order to explore the effects of free streaming on SPH evolution. Initial simulations are shown tracking Knudsen and Reynolds numbers of individual SPH particles with and without Freestream.