Quasi-particle model for lattice QCD: quark-gluon plasma in heavy ion collisions

TL;DR

This paper introduces a quasi-particle model for the lattice QCD equation of state in the deconfined quark-gluon plasma, accurately capturing interactions and enabling calculation of transport properties like shear viscosity.

Contribution

The study develops an exact mapping of the interaction effects to an effective fugacity, providing a novel way to analyze the quark-gluon plasma's thermodynamics and transport coefficients.

Findings

Exact mapping of interaction to effective fugacity

Determination of modified dispersion relations

Interactions significantly reduce shear viscosity

Abstract

We propose a quasi-particle model to describe the lattice QCD equation of state for pure SU(3) gauge theory in its deconfined state, for $T \ge 1.5T_c$. The method involves mapping the interaction part of the equation of state to an effective fugacity of otherwise non-interacting quasi-gluons. We find that this mapping is exact. Using the quasi-gluon distribution function, we determine the energy density and the modified dispersion relation for the single particle energy, in which the trace anomaly is manifest. As an application, we first determine the Debye mass, and then the important transport parameters, {\it viz}, the shear viscosity, $\eta$ and the shear viscosity to entropy density ratio, $\eta/{\mathcal S}$. We find that both $\eta$ and $\eta/{\mathcal S}$ are sensitive to the interactions, and that the interactions significantly lower both $\eta$ and $\eta/\mathcal S$.