Transport coefficients for hard-sphere relativistic gas.

Transport coefficients are of crucial importance in theoretical as well as experimental studies. Despite substantial research on classical hard sphere or disk gases in low- and high-density regimes, a thorough investigation of transport coefficients for massive relativistic systems is missing in the literature. In this work a fully relativistic molecular dynamics simulation is employed to numerically obtain the transport coefficients of a hard sphere relativistic gas based on Helfand-Einstein expressions. The numerical data are then used to check the accuracy of Chapmann-Enskog (CE) predictions in a wide range of temperature. The results indicate that while simulation data in low-temperature regime agrees very well with theoretical predictions, it begins to show deviations as temperature rises, except for the thermal conductivity which fits very well to CE theory in the whole range of temperature. Since our simulations are done in low density regimes, where CE approximation is expected to be valid, the observed deviations can be attributed to the inaccuracy of linear CE theory in extremely relativistic cases.