Effect of bulk viscosity on Elliptic Flow near QCD phase transition

Abstract

Effects of the bulk viscosity on the elliptic flow are studied. To introduce a realistic equation of state and transport coefficients, we apply the results of the lattice QCD and hadron resonance gas calculations for these quantities. We found that the bulk viscosity acts in a non trivial manner on the elliptic flow $v_{2}$. The reduction of $v_{2}$ is more effective at low $p_{T}$ compared to the case of shear viscosity, whereas at high $p_{T}$, the situation is reversed, leading to $v_{2}$ enhancement. We argue that this is caused by the competition of the critical behaviors of the equation of state and the transport coefficients. We further found that Grad's method with the 14 moments approximation is not applicable to estimate the viscous effects for the one-particle distribution function at the freeze out.