We solve the relativistic Riemann problem in viscous matter using the relativistic Boltzmann equation and the relativistic causal dissipative fluid-dynamical approach of Israel and Stewart. Comparisons between these two approaches clarify and point out the regime of validity of second-order fluid dynamics in relativistic shock phenomena. The transition from ideal to viscous shocks is demonstrated by varying the shear viscosity to entropy density ratio $\eta /s$. We also find that a good agreement between these two approaches requires a Knudsen number $\text{Kn}<1/2$.

• Received 7 June 2010

DOI:https://doi.org/10.1103/PhysRevC.82.024910