Towards compressed baryonic matter densities: thermodynamics and transport coefficients

TL;DR

This paper investigates the thermodynamic and transport properties of hot, dense quantum chromodynamic matter using three effective models, revealing how these properties vary with baryon density and highlighting violations of classical laws.

Contribution

It provides a comparative analysis of thermodynamic and transport coefficients across three effective QCD models at varying baryon densities, including novel insights into Lorenz ratio behavior.

Findings

Lorenz ratio increases rapidly at low baryon chemical potential

Shear viscosity to entropy density ratio remains nearly constant at low density

Transport properties show qualitative similarities with electron-hole plasma in graphene

Abstract

We study the thermodynamic and transport properties of hot and dense quantum chromodynamic matter expected to be produced in low-energy heavy-ion collisions, using three different effective quantum chromodynamic frameworks: the Nambu--Jona-Lasinio model, the chiral effective model, and the hadron resonance gas model. We briefly outline the theoretical formulation of thermodynamic quantities and transport coefficients within these approaches, where quarks are treated with effective masses in the Nambu--Jona-Lasinio and chiral effective models, and hadronic degrees of freedom are employed in the hadron resonance gas model. The transport coefficients are evaluated using the Boltzmann transport equation in the relaxation-time approximation. Following the theoretical overview, we present a comprehensive analysis of the behavior of these quantities as functions of the baryon chemical potential or net baryon density. The Lorenz ratio $\kappa/(\sigma T)$ is found to increase rapidly-indicating a strong violation of the Wiedemann-Franz law in the low-$\mu_{B}$ regime--while approaching the universal value at higher baryon chemical potentials or densities. The shear-viscosity-to-entropy-density ratio $\eta/s$ remains nearly constant at low $\mu_{B}$ but exhibits a gradual increase as $\mu_{B}$ grows. We also discuss the qualitative similarities of these trends with those observed in the electron-hole plasma of graphene, an emergent quasi-relativistic system characterized by massless energy-momentum dispersion.