Approaching Stable Quark Matter

TL;DR

This paper investigates the stability of quark matter using a combination of lattice QCD and perturbative QCD, setting bounds on key parameters and exploring the conditions under which quark matter could be stable.

Contribution

It introduces a novel framework combining Lattice QCD and perturbative QCD to constrain the bag parameter and assess quark matter stability.

Findings

Current data bounds the bag parameter B^{1/4} to be less than approximately 160 MeV.

Stable 2-flavor quark matter remains possible under certain conditions.

Stable 2+1-flavor quark matter is excluded assuming deconfinement and chiral symmetry restoration.

Abstract

The determination of whether the ground state of baryon matter in Quantum Chromodynamics (QCD) is the ordinary nucleus or a quark matter state remains a long-standing question in physics. A critical parameter in this investigation is the bag parameter $B$, which quantifies the QCD vacuum energy and can be computed using nonperturbative methods such as Lattice QCD (LQCD). By combining the equation of state derived from perturbative QCD (pQCD) with the bag parameter to fit the LQCD-simulated data for isospin-dense matter, we address the stability of quark matter within the LQCD+pQCD framework. Our findings suggest that the current data imposes an upper bound on $B^{1/4} \lesssim 160$ MeV, approaching a conclusive statement on quark matter stability. Given the lower bound on $B$ from the quark condensate contribution to the vacuum energy, the stable 2-flavor quark matter remains possible, whereas the stable 2+1-flavor quark matter is excluded, assuming complete deconfinement and chiral-symmetry restoration and the reliability of pQCD at baryon chemical potentials around the proton mass. Additionally, we derive more general thermodynamic bounds on the quark matter energy-per-baryon and $B$, which, while weaker, provide complementary insights.