Shear viscosity at finite baryon densities

TL;DR

This paper calculates the shear viscosity to entropy density ratio at finite baryon densities using a hadron resonance gas model and compares it with QCD-based results, revealing implications for initial conditions in hydrodynamics.

Contribution

It introduces a method to compute shear viscosity at finite baryon densities using the HRG model and matches it with QCD calculations across different temperature and chemical potential profiles.

Findings

Profiles of shear viscosity over entropy density vary with temperature and baryon chemical potential.

Higher initial baryon densities are needed to reach the same freeze-out conditions.

The results impact the understanding of initial conditions in heavy-ion collision hydrodynamics.

Abstract

We use the excluded volume Hadron Resonance Gas (HRG) model with the most up-to-date hadron list to calculate $\eta T/w$ at low temperatures and at finite baryon densities $\rho_B$. This $\eta T/w$ is then matched to a QCD-based shear viscosity calculation of the QGP for different profiles of $\eta T/w$ across {T,$\mu_{B}$} including cross-over and critical point transitions. When compared to ideal hydrodynamic trajectories across {T,$\mu_{B}$}, we find that the $\eta T/w(T,\mu_B)$ profiles would require initial conditions at much larger baryon density to reach the same freeze-out point.