The equation of state in lattice QCD: with physical quark masses towards the continuum limit

TL;DR

This work computes the QCD equation of state at vanishing chemical potential using lattice QCD with physical quark masses and two lattice spacings ($N_t=4,6$), aiming toward the continuum limit. It employs a Symanzik-improved gauge action, stout-link improved staggered fermions, and an exact RHMC algorithm, keeping the system on a line of constant physics to control systematic effects. The pressure, energy density, entropy density, speed of sound, and quark number susceptibilities are obtained via an integral method and presented as functions of $T/T_c$, with scale set from intermediate-distance potentials rather than the string tension. The results indicate reduced lattice artefacts and improved control over discretization errors, though a robust continuum extrapolation requires simulations at $N_t=8$ or finer.

Abstract

The equation of state of QCD at vanishing chemical potential as a function of temperature is determined for two sets of lattice spacings. Coarser lattices with temporal extension of N_t=4 and finer lattices of N_t=6 are used. Symanzik improved gauge and stout-link improved staggered fermionic actions are applied. The results are given for physical quark masses both for the light quarks and for the strange quark. Pressure, energy density, entropy density, quark number susceptibilities and the speed of sound are presented.