Viscous hydrodynamics with bulk viscosity – uncertainties from relaxation time and initial conditions

Bulk viscosity suppresses elliptic flow ν2, as does shear viscosity. It can thus not be neglected when extracting the shear viscosity from elliptic flow data. We here explore uncertainties in the bulk viscous contribution to viscous ν2 suppression that arise from presently uncontrolled uncertainties in the initial value of the bulk viscous pressure and its microscopic relaxation time.