begin{center}(attention : jour inhabituel / unusual day)end{center} To stuty the effect of viscosity in hydrodynamical approach of heavy ion reaction is very important to extract the correct information on the dynamics. However, the relativistic treatment of viscosity introduces both conceptual and technical difficulties. The Landau theory for the dissipative hydrodynamics is known to be unstable and not causal. Here, we present the new approach which cures the problem of acausality in the Landau theory. We compare our theory to the second order theories by Muller, Israel and Stewart. Since our theory is much simpler to be implemented, we present some numerical examples of viscous effects.

Université Fédérale de Rio de Janeiro