2+1 dimensional hydrodynamics including bulk viscosity: a systematics study

TL;DR

This study investigates how nonzero bulk viscosity near the QCD crossover temperature affects particle spectra and flow in relativistic heavy-ion collisions using Israel-Stewart hydrodynamics, highlighting the limitations of current correction methods.

Contribution

It systematically compares the effects of bulk and shear viscosity on hydrodynamic evolution and freezeout in 2+1D relativistic fluids, including the applicability limits of bulk viscous corrections.

Findings

Bulk viscosity impacts particle spectra and flow observables.

The Grad's 14-moment method is valid only for low bulk viscosity values.

The study provides constraints on the ratio of bulk to shear viscosity for accurate freezeout modeling.

Abstract

We have studied the effect of nonzero bulk viscosity with peak near the lattice QCD predicted crossover temperature $T_{co}\sim 175 MeV$ on charged particle transverse momentum spectra and elliptic flow. The Israel-Stewart theory of 2nd order causal dissipative relativistic fluid dynamics is used to simulate the space time evolution of the matter formed in Au-Au collisions at $\sqrt{s_{NN}}$=200 GeV assuming longitudinal boost invariance. A systematic comparison of temperature, transverse velocity, spatial and momentum anisotropy evolution of the ideal, bulk and shear viscous fluid has been carried out. Two different temperature dependent forms of $\zeta/s$ and a constant $\eta/s$ was used. Both the bulk and shear viscous correction to the ideal freezeout distribution function are included. The dissipative correction to the freezeout distribution for bulk viscosity was calculated using Grad's fourteen moment method. From our simulation we show that the method is applicable only for $\zeta/s < 0.005\times\eta/s|_{KSS}$ for freezeout temperatures 130 and 160 MeV.