Hot quark matter and (proto-) neutron stars

Abstract

In part one of this paper, we use a non-local extension of the 3-flavor Polyakov-Nambu-Jona-Lasinio model, which takes into account flavor-mixing, momentum dependent quark masses, and vector interactions among quarks, to investigate the possible existence of a spinodal region (determined by the vanishing of the speed of sound) in the QCD phase diagram and determine the temperature and chemical potential of the critical end point. In part two of the paper, we investigate the quark-hadron composition of baryonic matter at zero as well as non-zero temperature. This is of great topical interest for the analysis and interpretation of neutron star merger events such as GW170817. With this in mind, we determine the composition of proto-neutron star matter for entropies and lepton fractions that are typical of such matter. These compositions are used to delineate the evolution of proto-neutron stars to neutron stars in the baryon-mass versus gravitational-mass diagram. The hot stellar models turn out to contain significant fractions of hyperons and ∆-isobars but no deconfined quarks. The latter, are found to exist only in cold neutron stars. I. INTRODUCTIONExploring the thermodynamic behavior of the quark-gluon plasma and its associated equation of state (EoS) has become one of the forefront areas of modern physics. The properties of such matter are being probed with the Relativistic Heavy Ion Collider (RHIC) at BNL and the Large Hadron Collider (LHC) at CERN, and great advances in our understanding of such matter are expected from the next generation of high density experiments at the Facility for Antiproton and Ion Research (FAIR at GSI) [1, 2], the Nuclotron-bases Ion Collider fAcility (NICA at JINR) [3, 4], the Japan Proton Accelerator Research Complex (J-PARC at Tokai campus of JAEA) [5], the Super Proton Synchrotron (SPS at CERN) [6] and the Beam Energy Scan (BES at BNL) [7].Depending on temperature T , and baryon chemical potential µ, the deconfined phase of quarks and gluons is believed to exist at two extreme regions in the phase diagram of quantum chromodynamics (QCD). The first regime corresponds to T >> µ, which was the case in the early Universe where the temperature was hundreds of MeV but the net baryon number density was very low. Secondly, it is theorized that quark deconfinement occurs also at low temperatures but very high chemical potential, T << µ, that is, at conditions which exist in the inner cores of (proto-) neutron stars [8]. Portions of the phase diagram lying between these two extreme physical regimes can be probed with relativistic collision experiments.Effective field-theoretical models such as the Nambu-Jona-Lasinio model and its extensions [9-13] as well as lattice QCD (LQCD) calculations [14-16] predict a smooth crossover of nuclear matter to quark matter in the low density but high temperature regime of the phase diagram. On the other hand, in the low temperature but high chemical potential regime the hadron-quark phase transition is likely be of first-order [17]. Some recent works [18,...

Strong-Interaction Matter under Extreme Conditions from Chiral Quark Models with Nonlocal Separable Interactions

“…Moreover, it is argued that GW170817 data also imply a general upper limit of about 2.3M for the mass of a cold spherical NS [221]. These constraints have been taken into account for the analysis of EoS arising from hybrid star models that include nlNJL approaches for quark matter [222][223][224][225][226][227][228].…”

Phases of Hadron-Quark Matter in (Proto) Neutron Stars

“…Due to the Fermi pressure of the nucleons, the collapse stops when nuclear matter density is reached and the core bounces back. Shortly after core bounce (some 10 ms) a hot, lepton rich neutron star, called a proto-neutron star, is formed [8][9][10][11][12][13]. This star consists of a shocked envelope with an entropy per baryon of s ∼ 4-10 (in units of the Boltzmann constant) and an unshocked core with s ∼ 1.…”

Thermodynamic potential for quark-qluon plasma with finite quark mass and chemical potential

“…The calculation of the impact of this phase diagram on neutron stars would require a detailed model for the nuclear equation of state at high density. Nevertheless, the studies based upon the NLJ nuclear models are quite similar to figure 6 [36,37]. In [37] it was proposed that g-modes in neutron stars might be a means to detect the QCD transition.…”

“…There have been a number of efforts to explore the phase diagram in the literature including that obtained from Lattice QCD calculations such as [29][30][31], chemical freeze-out from relativistic heavy ion collision data [32][33][34][35] and in recent NJL models which explore the impact of the phase transition on the physics neutron stars [36,37]. As noted above lattice gauge theory with a finite mass s-quark leads to a high temperature phase transition at a temperature in the range of 145 MeVT c 170 Mev [13,30], possibly favoring the lower end of the range of T c =154±9 as in [29].…”