Sequential deconfinement of quark flavors in neutron stars

Abstract

A scenario is suggested in which the three light quark flavors are sequentially deconfined under increasing pressure in cold asymmetric nuclear matter as found, for example, in neutron stars. The basis for this analysis is a chiral quark matter model of Nambu-Jona-Lasinio (NJL) type with diquark pairing in the spin-1 single-flavor, spin-0 two-flavor, and three-flavor channels. Nucleon dissociation sets in at about the saturation density, n 0 , when the down-quark Fermi sea is populated (d-quark drip line) because of the flavor asymmetry induced by β equilibrium and charge neutrality. At about 3n 0 , u-quarks appear and a two-flavor color superconducting (2SC) phase is formed. The s-quark Fermi sea is populated only at still higher baryon density, when the quark chemical potential is of the order of the dynamically generated strange quark mass. Two different hybrid equations of state (EOSs) are constructed using the Dirac-Brueckner Hartree-Fock (DBHF) approach and the EOS of Shen et al. [H. Shen, H. Toki, K. Oyamatsu, and K. Sumiyoshi, Nucl. Phys. A637, 435 (1998)] in the nuclear matter sector. The corresponding hybrid star sequences have maximum masses of 2.1 and 2.0 M , respectively. Twoand three-flavor quark-matter phases exist only in gravitationally unstable hybrid star solutions in the DBHF case, whereas the Shen-based EOSs produce stable configurations with a 2SC phase component in the core of massive stars. Nucleon dissociation via d-quark drip could act as a deep crustal heating process, which apparently is required to explain superbursts and cooling of x-ray transients.

Simultaneous Chiral Symmetry Restoration and Deconfinement Consequences for the QCD Phase Diagram

“…This can lead to interesting scenarios(cf. Blaschke et al 2009). However, in this work we model an EoS where light flavors appear at the same critical baryon chemical potential analogous to the results obtained with the "standard" approach for first-order phase transitions.…”

Strange matter prospects within the string-flip model

“…We observe an onset of strange quarks at much lower densities than the deconfinement phase transition. This leads to the simultaneous appearance of all flavours, in contrast to the commonly employed NJL-type models with sequential deconfinement [5,26]. We have found that the inclusion of the strange quark flavor lowers the onset of the deconfinement transition, but SFM parameters can be selected such that hybrid star sequences in the mass-radius diagram of two-and three-flavor quark matter are nearly indistinguishable.…”

High-mass twins & resolution of the reconfinement, masquerade and hyperon puzzles of compact star interiors

“…The description of normal quark matter phases with two and three flavours is straightforward and shows the qualitative difference to bag models of quark matter already: light and strange quark flavours appear sequentially [29] due to the fact that different chemical potentials are required to reach the dynamically generated light and strange quark masses, so that strange quarks appear in cold quark matter only at high densities, eventually too high for CS interiors [30,31,32].…”