Kinetic equilibration from a radiative transport

Kinetic equilibration during the early stage of a relativistic heavy ion collision is studied using a radiative transport model. Thermalization is found to dominate over expansion with medium regulated cross sections. Pressure anisotropy shows an approximate alpha_s scaling when radiative processes are included. It approaches an asymptotic time evolution on a time scale of 1 to 2 fm/c. Energy density is also found to approach an asymptotic time evolution that decreases slower than the ideal hydro evolution. These observations indicate that viscosity is important during the early longitudinal expansion phase of a relativistic heavy ion collision.