Interplay of shear and bulk viscosity in generating flow in heavy-ion collisions

TL;DR

This study uses viscous hydrodynamics to analyze how shear and bulk viscosities influence flow patterns in heavy-ion collisions, revealing that bulk viscosity effects are mitigated by relaxation dynamics near the phase transition.

Contribution

It provides a detailed investigation of bulk and shear viscosity effects on flow in heavy-ion collisions, highlighting the role of relaxation times and phase transition dynamics.

Findings

Bulk viscosity effects are partially offset by relaxation times near T_c.

Small shear viscosity values can be reliably extracted despite bulk effects.

Temperature-dependent relaxation times influence flow suppression.

Abstract

We perform viscous hydrodynamic calculations in 2+1 dimensions to investigate the influence of bulk viscosity on the viscous suppression of elliptic flow in non-central heavy-ion collisions at RHIC energies. Bulk and shear viscous effects on the evolution of radial and elliptic flow are studied with different model assumptions for the transport coefficients. We find that the temperature dependence of the relaxation time for the bulk viscous pressure, especially its critical slowing down near the quark-hadron phase transition at T_c, partially offsets effects from the strong growth of the bulk viscosity itself near T_c, and that even small values of the specific shear viscosity eta/s of the fireball matter can be extracted without large uncertainties from poorly controlled bulk viscous effects.