Equation of state and sound velocity of hadronic gas with hard-core interaction

TL;DR

This paper investigates the thermodynamic properties of hot, dense hadronic gases with hard-core interactions using two pressure parametrizations, showing the broader applicability of the Carnahan-Starling model and its implications for sound velocity limits.

Contribution

It introduces the use of the Carnahan-Starling equation of state for hadronic gases, extending the valid density range compared to traditional excluded volume models.

Findings

Carnahan-Starling approach applies to higher hadronic densities.

Superluminal sound velocities occur only at very high densities.

The model aligns with deconfinement physics at high densities.

Abstract

Thermodynamic properties of hot and dense hadronic systems with a hard-sphere interaction are calculated in the Boltzmann approximation. Two parametrizations of pressure as a function of density are considered: the first one, used in the excluded volume model and the second one, suggested earlier by Carnahan and Starling. The results are given for one-component systems containing only nucleons or pions, as well as for chemically equilibrated mixtures of pions, nucleons and delta resonances. It is shown that the Carnahan-Starling approach can be used in a much broader range of hadronic densities as compared to the excluded volume model. In this case superluminal sound velocities appear only at very high densities, in the region where the deconfinement effects should be already important.