Equation of state at finite net-baryon density using Taylor coefficients up to sixth order

TL;DR

This paper constructs an equation of state at finite net-baryon density using lattice QCD Taylor coefficients up to sixth order, connecting it smoothly to the hadron resonance gas model and analyzing the convergence at various densities.

Contribution

It introduces a method to derive the equation of state at finite density from lattice QCD data up to sixth order, incorporating hadron mass dependencies and ensuring smooth matching with the hadron resonance gas.

Findings

Equation of state matches hadron resonance gas at low temperature.

Second order Taylor expansion is valid only at low densities.

Sixth order expansion converges at densities with s/n_B > 40.

Abstract

We employ the lattice QCD data on Taylor expansion coefficients up to sixth order to construct an equation of state at finite net-baryon density. When we take into account how hadron masses depend on lattice spacing and quark mass, the coefficients evaluated using the p4 action are equal to those of hadron resonance gas at low temperature. Thus the parametrised equation of state can be smoothly connected to the hadron resonance gas equation of state. We see that the equation of state using Taylor coefficients up to second order is realistic only at low densities, and that at densities corresponding to s/n_B > 40, the expansion converges by the sixth order term.