1-2-3-flavor color superconductivity in compact stars

TL;DR

This paper models the sequential deconfinement of quark flavors in neutron stars, revealing phase transitions to color superconducting states and predicting a maximum star mass of 2.1 solar masses.

Contribution

It introduces a combined NJL and DBHF approach to describe flavor-dependent quark deconfinement and color superconductivity in compact stars.

Findings

Sequential flavor deconfinement occurs at increasing densities.

Two-flavor and three-flavor quark phases are unstable in stable stars.

Maximum hybrid star mass is 2.1 solar masses.

Abstract

We suggest a scenario where the three light quark flavors are sequentially deconfined under increasing pressure in cold asymmetric nuclear matter, e.g., as in neutron stars. The basis for our analysis is a chiral quark matter model of Nambu--Jona-Lasinio (NJL) type with diquark pairing in the spin-1 single flavor (CSL) and spin-0 two/three flavor (2SC/CFL) channels, and a Dirac-Brueckner Hartree-Fock (DBHF) approach in the nuclear matter sector. We find that nucleon dissociation sets in at about the saturation density, n_0, when the down-quark Fermi sea is populated (d-quark dripline) due to the flavor asymmetry imposed by beta-equilibrium and charge neutrality. At about 3n_0 u-quarks appear forming a two-flavor color superconducting (2SC) phase, while the s-quark Fermi sea is populated only at still higher baryon density. The hybrid star sequence has a maximum mass of 2.1 M_sun. Two- and three-flavor quark matter phases are found only in gravitationally unstable hybrid star solutions.