Thermodynamics of strongly interacting matter in a hybrid model

TL;DR

This paper develops a hybrid model combining the Polyakov-Nambu-Jona-Lasinio and Hadron Resonance Gas models to accurately describe the thermodynamics and fluctuations of strongly interacting matter, aligning well with lattice QCD data at low temperatures.

Contribution

The paper introduces a hybrid approach that incorporates hadronic effects into the Polyakov-Nambu-Jona-Lasinio model, improving agreement with lattice QCD results.

Findings

The hybrid model matches lattice QCD data for the equation of state at low temperatures.

The model accurately reproduces fluctuations and correlations of conserved charges.

Inclusion of hadrons resolves discrepancies at low temperatures.

Abstract

The equation of state and fluctuations of conserved charges in a strongly interacting medium under equilibrium conditions form the baseline upon which various possible scenarios in relativistic heavy-ion collision experiments are built. Many of these quantities have been obtained in the lattice QCD framework with reliable continuum extrapolations. Recently the Polyakov$-$Nambu$-$Jona-Lasinio model has been reparametrized to some extent to reproduce quantitatively the lattice QCD equation of state at vanishing chemical potentials. The agreement was precise except at low temperatures, possibly due to inadequate representation of the hadronic degrees of freedom in the model. This disagreement was also observed for some of the fluctuation and correlations considered. Here we address this issue by introducing the effects of hadrons through the Hadron Resonance Gas model. The total thermodynamic potential is now a weighted sum of the thermodynamic potential of the Polyakov$-$Nambu$-$Jona-Lasinio model and that of the Hadron Resonance Gas model. We find that the equation of state and the fluctuations and correlations obtained in this hybrid model agrees satisfactorily with the lattice QCD data in the low temperature regime.