Shear viscosity from perturbative Quantum Chromodynamics to the hadron resonance gas at finite baryon, strangeness, and electric charge densities

TL;DR

This paper develops a framework to calculate shear viscosity in QCD at finite baryon, strangeness, and charge densities by interpolating between perturbative QCD and hadron resonance gas models, revealing complex density dependence.

Contribution

It introduces a novel interpolation method to estimate shear viscosity across a wide range of finite BSQ densities in QCD, bridging two theoretical limits.

Findings

Shear viscosity varies non-trivially with BSQ densities.

Different density dependencies are observed in pQCD and hadron resonance gas models.

A continuous framework for shear viscosity at finite densities is established.

Abstract

Through model-to-data comparisons from heavy-ion collisions, it has been shown that the Quark Gluon Plasma has an extremely small shear viscosity at vanishing densities. At large baryon densities, significantly less is known about the nature of the shear viscosity from Quantum Chromodynamics (QCD). Within heavy-ion collisions, there are three conserved charges: baryon number (B), strangeness (S), and electric charge (Q). Here we calculate the shear viscosity in two limits using perturbative QCD and an excluded-volume hadron resonance gas at finite BSQ densities. We then develop a framework that interpolates between these two limits such that shear viscosity is possible to calculate across a wide range of finite BSQ densities. We find that the pQCD and hadron resonance gas calculations have different BSQ densities dependence such that a rather non-trivial shear viscosity appears at finite densities.