Unlocking Color and Flavor in Superconducting Strange Quark Matter

TL;DR

This paper investigates the phase diagram of dense quark matter, revealing how color-flavor locking and chiral symmetry breaking depend on density and strange quark mass, with implications for the connection between quark and baryonic matter.

Contribution

It provides a detailed analysis of the phase transitions and symmetry properties of dense quark matter, including a model-independent argument and a quantitative model for the phase diagram.

Findings

Color-flavor locked phase exists at high density for any finite strange quark mass.

Chiral symmetry remains broken in dense quark matter at realistic strange quark masses.

A first order transition occurs from the color-flavor locked phase to a color superconducting phase as density decreases.

Abstract

We explore the phase diagram of strongly interacting matter with massless u and d quarks as a function of the strange quark mass m_s and the chemical potential mu for baryon number. Neglecting electromagnetism, we describe the different baryonic and quark matter phases at zero temperature. For quark matter, we support our model-independent arguments with a quantitative analysis of a model which uses a four-fermion interaction abstracted from single-gluon exchange. For any finite m_s, at sufficiently large mu we find quark matter in a color-flavor locked state which leaves a global vector-like SU(2)_{color+L+R} symmetry unbroken. As a consequence, chiral symmetry is always broken in sufficiently dense quark matter. As the density is reduced, for sufficiently large m_s we observe a first order transition from the color-flavor locked phase to a color superconducting phase analogous to that in two flavor QCD. At this unlocking transition chiral symmetry is restored. For realistic values of m_s our analysis indicates that chiral symmetry breaking may be present for all densities down to those characteristic of baryonic matter. This supports the idea that quark matter and baryonic matter may be continuously connected in nature. We map the gaps at the quark Fermi surfaces in the high density color-flavor locked phase onto gaps at the baryon Fermi surfaces at low densities.