η(T)/s (T) and collective flow in chiral hydrodynamics

Using relativistic conformal hydrodynamics coupled to the linear $\sigma$ model we study the evolution of matter created in heavy--ion collisions. We focus the study on the influence of the dynamics of the chiral fields on the charged-hadron elliptic flow $v_2$ for a temperature--independent as well as for a temperature--dependent $\eta/s$ that is calculated from kinetic theory. We find that $v_2$ is not very sensitive to the coupling of chiral fields to the hydrodynamic evolution, but the temperature dependence of $\eta/s$ plays a much bigger role on this observable.