Bounding the QCD Equation of State with the Lattice

TL;DR

This paper demonstrates how lattice QCD simulations can provide an upper bound on the QCD equation of state at high densities, with implications for neutron star physics, by analyzing pressure bounds and quantum corrections.

Contribution

It introduces a method to bound the QCD pressure at high densities using sign-problem-free lattice simulations, highlighting the significance of quantum corrections.

Findings

Lattice QCD can set an upper bound on the QCD pressure at high densities.

The difference between the bound and true pressure is of order alpha^3 P.

Calculations of a specific Feynman diagram could reduce remaining uncertainties.

Abstract

The equation of state of QCD matter at high densities is relevant for neutron star structure and for neutron star mergers and has been a focus of recent work. We show how lattice QCD simulations, free of sign problems, can provide an upper bound on the pressure as a function of quark chemical potentials. We show that at large chemical potentials this bound should become quite sharp; the difference between the upper bound on the pressure P-phase-quenched and the true pressure P is of order alpha^3 P. The corrections arise from a single Feynman diagram; its calculation would render remaining corrections of order alpha^4 P.