Bulk viscosity-driven suppression of shear viscosity effects on the flow harmonics at RHIC

TL;DR

This study uses a new hydrodynamical model to show that bulk viscosity can counteract shear viscosity effects on flow harmonics at RHIC, impacting estimates of quark-gluon plasma properties.

Contribution

It introduces a relativistic 2+1 hydrodynamical code including both shear and bulk viscosities, revealing bulk viscosity's role in modifying flow harmonic suppression.

Findings

Bulk viscosity reduces shear viscosity's suppression of flow harmonics.

Inclusion of bulk viscosity aligns flow harmonic predictions closer to ideal hydrodynamics.

Re-evaluation of shear viscosity estimates in quark-gluon plasma may be necessary.

Abstract

The interplay between shear and bulk viscosities on the flow harmonics, $v_n$'s, at RHIC is investigated using the newly developed relativistic 2+1 hydrodynamical code v-USPhydro that includes bulk and shear viscosity effects both in the hydrodynamic evolution and also at freeze-out. While shear viscosity is known to attenuate the flow harmonics, we find that the inclusion of bulk viscosity decreases the shear viscosity-induced suppression of the flow harmonics bringing them closer to their values in ideal hydrodynamical calculations. Depending on the value of the bulk viscosity to entropy density ratio, $\zeta/s$, in the quark-gluon plasma, the bulk viscosity-driven suppression of shear viscosity effects on the flow harmonics may require a re-evaluation of the previous estimates of the shear viscosity to entropy density ratio, $\eta/s$, of the quark-gluon plasma previously extracted by comparing hydrodynamic calculations to heavy ion data.