Isothermal and isentropic speed of sound in (2+1)-flavor QCD at non-zero baryon chemical potential

TL;DR

This paper investigates the speed of sound in (2+1)-flavor QCD at non-zero baryon chemical potential, comparing lattice QCD results with hadron resonance gas models, and highlighting differences at low temperatures.

Contribution

It provides new lattice QCD calculations of the isothermal and isentropic speed of sound in QCD at finite baryon chemical potential, and compares these with hadron resonance gas models.

Findings

Differences between $c^2_T$ and $c^2_s$ at low temperature due to light mesons.

Lattice results align with hadron resonance gas models at certain conditions.

Insights into charge fluctuation cumulants related to speed of sound.

Abstract

Recently interest in calculations of the speed of sound in QCD under conditions like constant temperature $c^2_T$ or constant entropy per net baryon number $c^2_s$ arose in the discussion of experimental results coming from heavy ion experiments. It has been stressed that the former in particular is closely related to higher order cumulants of conserved charge fluctuations that are calculated in lattice QCD. We present here results on $c^2_T$ and $c^2_s$ and compare results at vanishing strangeness chemical potential and vanishing net strangeness number with hadron resonance gas model calculations. We stress the difference of both observables at low temperature arising from the light meson sector, which does not contribute to $c^2_T$.