Hadron Resonance Gas Equation of State from Lattice QCD

TL;DR

This study analyzes lattice QCD data at low temperatures using extended hadron resonance gas models, finding evidence for both repulsive interactions and exponential mass spectrum effects influencing thermodynamics.

Contribution

It demonstrates the simultaneous presence of excluded volume and Hagedorn spectrum effects in modeling QCD thermodynamics at small temperatures.

Findings

Both models contribute significantly to thermodynamic properties.

Excluded volume effects suppress thermodynamic functions.

Hagedorn spectrum enhances thermodynamic functions.

Abstract

The Monte Carlo results in lattice QCD for the pressure and energy density at small temperature $T < 155$ MeV and zero baryonic chemical potential are analyzed within the hadron resonance gas model. Two extensions of the ideal hadron resonance gas are considered: the excluded volume model which describes a repulsion of hadrons at short distances and Hagedorn model with the exponential mass spectrum. Considering both of these models one by one we do not find the conclusive evidences in favor of any of them. The controversial results appear because of rather different sensitivities of the pressure and energy density to both excluded volume and Hagedorn mass spectrum effects. On the other hand, we have found a clear evidence for a simultaneous presence of both of them. They lead to rather essential contributions: suppression effects for thermodynamical functions of the hadron resonance gas due to the excluded volume effects and enhancement due to the Hagedorn mass spectrum.