Cold Quark Matter

TL;DR

This paper calculates the equation of state for cold dense quark matter using perturbation theory, exploring the stability of strange quark matter and implications for compact star properties.

Contribution

It provides a perturbative calculation of cold quark matter's equation of state up to O(alpha_s^2), including effects of a massive strange quark, and discusses implications for stellar stability.

Findings

Perturbation theory converges well above 1 GeV chemical potential.

A narrow parameter range allows for absolutely stable strange quark matter.

Hybrid stars can reach masses up to approximately 2 solar masses, consistent with observations.

Abstract

We perform an O(alpha_s^2) perturbative calculation of the equation of state of cold but dense QCD matter with two massless and one massive quark flavor, finding that perturbation theory converges reasonably well for quark chemical potentials above 1 GeV. Using a running coupling constant and strange quark mass, and allowing for further non-perturbative effects, our results point to a narrow range where absolutely stable strange quark matter may exist. Absent stable strange quark matter, our findings suggest that quark matter in compact star cores becomes confined to hadrons only slightly above the density of atomic nuclei. Finally, we show that equations of state including quark matter lead to hybrid star masses up to M~2M_solar, in agreement with current observations. For strange stars, we find maximal masses of M~2.75M_solar and conclude that confirmed observations of compact stars with M>2M_solar would strongly favor the existence of stable strange quark matter.