Speed of sound and liquid-gas phase transition in nuclear matter

TL;DR

This paper studies the speed of sound in nuclear matter at finite temperature and density, revealing its connection to the liquid-gas phase transition and phase diagram boundaries, with implications for understanding strongly interacting matter.

Contribution

It provides a detailed analysis of the sound speed behavior near the nuclear liquid-gas phase transition and derives the phase boundary where sound velocity vanishes.

Findings

Sound speed is linked to the liquid-gas phase transition.

The adiabatic sound speed remains nonzero at the critical endpoint.

Identifies regions where the sound wave equation breaks down.

Abstract

We investigate the speed of sound in nuclear matter at finite temperature and density~(chemical potential) in the nonlinear Walecka model. The numerical results suggest that the behaviors of sound speed are closely related to the the nuclear liquid-gas (LG) phase transition and the associated spinodal structure. The adiabatic sound speed is nonzero at the critical endpoint (CEP) in the mean field approximation. We further derive the boundary of vanishing sound velocity in the temperature-density phase diagram, and point out the region where the sound wave equation is broken. The distinction between the speed of sound in nuclear matter and that in quark matter contains important information about the equation of state of strongly interacting matter at intermediate and high density. We also formulate the relations between differently defined speed of sound using the fundamental thermodynamic relations.