Critical Point on the QCD Deconfining Phase Boundary

TL;DR

This paper investigates the critical point on the QCD deconfining phase boundary using thermodynamic and transport properties, confirming its existence and precise location through multiple indicators like entropy density, speed of sound, and shear viscosity ratios.

Contribution

The study extends previous work by identifying the critical point on the QCD phase boundary through thermodynamic and transport property analyses, providing a more precise characterization.

Findings

Entropy density difference vanishes at CP

Speed of sound difference vanishes at CP

Cusp in shear viscosity to entropy ratio indicates CP

Abstract

Ambiguities regarding the physics and the existence of the critical point (CP) on the QCD phase boundary still exist and the mist regarding the conjectured QCD phase boundary has not yet cleared. In this paper we extend our earlier study where we constructed a deconfining phase boundary using Gibbs' equilibrium conditions after using a quasiparticle equation of state (EOS) for quark gluon plasma (QGP) and an excluded volume EOS for the hadron gas (HG) and find the presence of a critical point on this phase boundary where the first order phase transition terminates. In this paper, we plot the difference in the normalized entropy density ($s/T^{3}$) between HG and QGP phases along the deconfining phase boundary and find that it vanishes at CP. Further we have shown the variation of the square of speed of sound ($c_{s}^{2}$) for the HG and QGP separately and find that the difference ($\Delta c_{s}^{2}$) between them along the deconfining phase boundary again vanishes at the CP of the boundary. We also plot the variation of shear viscosity to entropy density ratio ($\eta/s$) in HG as well as in QGP phases separately with respect to temperature at different baryonic chemical potential ($\mu_{B}$). The presence of a cusp like structure in $\eta/s$ again confirms the existence of CP on the deconfining phase boundary as predicted by some authors. These studies thus firmly indicate the precise location of CP as a second order phase transition point.