Free-streaming as a pre-equilibrium model for use with (3+1)-dimensional hydrodynamical evolution models

A (3+1)-dimensional free-streaming module has been developed that converts an initial energy momentum tensor for a system of massless partons with arbitrary initial energy density but zero collective flow at time zero into an evolved energy momentum tensor at any later time. By writing the evolved energy momentum tensor at that later time in hydrodynamic form one obtains non-trivial initial conditions, including initial collective flow profiles and dissipative flows, for subsequent hydrodynamic evolution.