The equation of state for two flavor QCD at finite density

TL;DR

This paper investigates the equation of state for two-flavor QCD at finite temperature and density using lattice simulations, revealing potential critical behavior near the phase transition.

Contribution

It introduces a Taylor expansion method to estimate thermodynamic quantities at finite density in two-flavor QCD with improved staggered fermions.

Findings

Quark number density fluctuations increase near the transition temperature.

Susceptibilities develop peaks as chemical potential increases.

Evidence suggests a critical endpoint in the phase diagram.

Abstract

We discuss the equation of state for QCD at non-zero temperature and density. We present results of a simulation for QCD with 2 flavors of p4-improved staggered fermions. Derivatives of $\ln {\cal Z}$ with respect to quark chemical potential $\mu_q$ up to fourth order are calculated, enabling estimates of the pressure, quark number density and associated susceptibilities as functions of $\mu_q$ via a Taylor series expansion. We also discuss the radius of convergence of the expansion as a function of temperature. It is found that the fluctuations in the quark number density increase in the vicinity of the phase transition temperature and the susceptibilities start to develop a pronounced peak as $\mu_q$ is increased. This suggests the presence of a critical endpoint in the $(T, \mu_q)$ plane.