Quark Matter Research Articles

Testing the phase transition parameters inside neutron stars with the production of protons and lambdas in relativistic heavy-ion collisions

We demonstrate the consistency of the quark deconfinement phase transition parameters in the beta-stable neutron star matter and in the nearly symmetric nuclear matter formed in heavy-ion collisions (HICs). We investigate the proton and $\mathrm{\ensuremath{\Lambda}}$ flow in $\mathrm{Au}+\mathrm{Au}$ collisions at 3 and $4.5\text{ }\text{ }\mathrm{GeV}/\mathrm{nucleon}$ incident beam energies with the pure hadron cascade version of a multiphase transport model. The phase transition in HICs and neutron stars is described based on a class of hybrid equations of state from the quark mean-field model for the hadronic phase and a constant-speed-of-sound parametrization for the high-density quark phase. The measurements of the anisotropic proton flow at $3\text{ }\text{ }\mathrm{GeV}/\mathrm{nucleon}$ by the STAR Collaboration favor a relatively low phase transition density lower than $\ensuremath{\sim}2.5$ times saturation density indicated by the gravitational wave and electromagnetic observations of neutron stars. And the proton flow data at the higher energy of $4.5\text{ }\text{ }\mathrm{GeV}/\mathrm{nucleon}$ can be used to effectively constrain the softness of high-density quark matter equations of state. Finally, compared to the proton flow, the $\mathrm{\ensuremath{\Lambda}}$ flow is found to be less sensitive and not constraining to the equations of state.

Investigating signatures of phase transitions in neutron-star cores

Neutron stars explore matter at the highest densities in the universe such that their inner cores might undergo a phase transition from hadronic to exotic phases, e.g., quark matter. Such a transition could be associated with nontrivial structures in the density behavior of the speed of sound, such as jumps and sharp peaks. Here, we employ a physics-agnostic approach to model the density dependence of the speed of sound in neutron stars and study to what extent the existence of nontrivial structures can be inferred from existing astrophysical observations of neutron stars. For this, we exhaustively study different equations of state, including as well those with explicit first-order phase transitions. We obtain a large number of different equation of states which reproduce the same astrophysical observations and obey the same physical constraints, such as mechanical stability and causality. Among them, some have nontrivial structures in the sound speed whereas others do not. We conclude that astrophysical information to date do not require the existence of a phase transition to quark matter in the density range explored in the core of neutron stars.

Reaching percolation and conformal limits in neutron stars

Generating an ensemble of equations of state that fulfill multimessenger constraints, we statistically determine the properties of dense matter found inside neutron stars (NSs). We calculate the speed of sound and trace anomaly and demonstrate that they are driven towards their conformal values at the center of maximally massive NSs. The local peak of the speed of sound is shown to be located at values of the energy and particle densities which are consistent with deconfinement and percolation conditions in QCD matter. We also analyze fluctuations of the net-baryon number density in the context of possible remnants of critical behavior. We find that the global maxima of the variance of these fluctuations emerge at densities beyond those found in the interiors of NSs.

Non-radial oscillation modes in hybrid stars: consequences of a mixed phase

We study the possibility of the existence of a deconfined quark matter in the core of neutron star (NS)s and its relation to non-radial oscillation modes in NSs and hybrid star (HS)s. We use relativistic mean field (RMF) models to describe the nuclear matter at low densities and zero temperature. The Nambu-Jona-Lasinio (NJL) model is used to describe the quark matter at high densities and zero temperature. A Gibbs construct is used to describe the hadron-quark phase transition (HQPT) at large densities. Within the model, as the density increases, a mixed phase (MP) appears at density about 2.5 times the nuclear matter saturation density (ρ 0) and ends at density about 5ρ 0 beyond which the pure quark matter phase appears. It turns out that a stable HS of maximum mass, M = 2.27 M ⊙ with radius R = 14 km (for NL3 parameterisation of nuclear RMF model), can exist with the quark matter in the core in a MP only. HQPT in the core of maximum mass HS occurs at radial distance, rc = 0.27R where the equilibrium speed of sound shows a discontinuity. Existence of quark matter in the core enhances the non-radial oscillation frequencies in HSs compared to NSs of the same mass. This enhancement is significantly large for the g modes. Such an enhancement of the g modes is also seen for a density dependent Bayesian (DDB) parmeterisation of the nucleonic EOS. The non-radial oscillation frequencies depend on the vector coupling in the NJL model. The values of g and f mode frequencies decrease with increase the vector coupling in quark matter.

Relativistic Hybrid Stars with Sequential First-order Phase Transitions in Light of Multimessenger Constraints

In this work, we consider the properties of compact stars in which quark matter has low- and high-density phases that are separated by a first-order phase transition. Thus, unlike the commonly considered case of a single phase transition from hadronic to quark matter, our models of hybrid stars contain sequential phase transitions from hadronic matter to low- and then to high-density quark matter phases. We extend our previous study of the parameter space of hybrid stars with a single phase transition to those with sequential phase transitions, taking into account the constraints on the mass and radius of neutron stars from the NICER experiment, the experimental inferences of the neutron skin thickness of the lead nucleus by the PREX-II experiment, and constraints on the tidal deformability from the gravitational-wave event GW170817. We determine the range of the masses for which both twin and triplet configurations, i.e., identical-mass stars with two and three different values of radii, arise.

Constraining the Equation of State of Hybrid Stars Using Recent Information from Multidisciplinary Physics

At the ultrahigh densities existing in the core of neutron stars (NSs), it is expected that a phase transition from baryonic to deconfined quark matter may occur. Such a phase transition would affect the underlying equation of state (EoS) as well as the observable astrophysical properties of NSs. Comparison of EoS model predictions with astronomical data from multimessenger signals then provides us an opportunity to probe the behavior of dense matter. In this work, we restrict the allowed parameter space of EoS models in NSs for both nucleonic (relativistic mean field model) and quark matter (MIT bag model) sectors by imposing state-of-the-art constraints from nuclear calculations, multimessenger astrophysical data, and perturbative quantum chromodynamics (pQCD). We systematically investigate the effect of each constraint on the parameter space of uncertainties using a cutoff filter scheme, as well as the correlations among the parameters and with NS astrophysical observables. Using the constraints, we obtain limits for maximum NS mass, maximum central density, as well as for NS radii and tidal deformability. Although pQCD constraints are only effective at very high densities, they significantly reduce the parameter space of the quark model. We also conclude that astrophysical data supports high values of the bag parameter B and disfavors the existence of a pure quark matter core in hybrid stars.

Five-dimensional strange quark matter cosmological model with string cloud

The work in this paper is devoted to the study of Kaluza–Klein (KK) cosmological model with strange quark matter attached to string cloud in the framework of metric version of [Formula: see text] gravity. By utilizing hybrid expansion law for average scale factor of the model i.e. [Formula: see text], here [Formula: see text] and [Formula: see text] are positive constants, we derive the solution of the field equations of KK model in the [Formula: see text] gravity. Various dynamical parameters of the model are obtained and their behavior is analyzed through graphical representation. We observe that the analysis of deceleration parameter exhibits a smooth transition of the universe from early decelerated phase to current accelerated epoch. Also, we discussed well-known state-finder parameters [Formula: see text] and [Formula: see text] planes which are analyzed by graphical representation.

Shear viscosity coefficient of magnetized QCD medium near chiral phase transition

We study the properties of the shear viscosity coefficient of quark matter at finite temperature and chemical potential near chiral phase transition in a strong background magnetic field. A strong magnetic field induces anisotropic features, phase-space Landau-level quantization, and if the magnetic field is sufficiently strong, interferes with prominent QCD phenomena such as dynamical quark mass generation, likely affecting the quark matter transport characteristics. The modified Nambu-Jona-Lasinio (NJL) model with inverse magnetic catalysis effect by fitting the Lattice QCD (LQCD) results is used to calculate the changes of quasiparticle related thermodynamic quantities, and the shear viscosity of the system medium, which is analyzed under the relaxation time approximation. We quantify the influence of the order of chiral phase transition and the critical endpoint on dissipative phenomena in such a magnetized medium. When the magnetic field exists, the shear viscosity coefficient of the dissipative fluid system can be decomposed into five different components. In strong field limit, we make a detailed study of the dependencies of $\eta_{2}$ and $\eta_{4}$ on temperature and magnetic field for the first order phase transition and critical endpoint transition. respectively. It is found that $\eta_{2}$ and $\eta_{4}$ both decrease with magnetic field and increase with temperature, and the discontinuities of $\eta_{2}$ and $\eta_{4}$ occur at the first order phase transition point.

Reverse phase transitions in binary neutron-star systems with exotic-matter cores

Multi-messenger observations of binary neutron star mergers provide a unique opportunity to constrain the dense-matter equation of state. Although it is known from quantum chromodynamics that hadronic matter will undergo a phase transition to exotic forms of matter, e.g., quark matter, the onset density of such a phase transition cannot be computed from first principles. Hence, it remains an open question if such phase transitions occur inside isolated neutron stars or during binary neutron star mergers, or if they appear at even higher densities that are not realized in the Cosmos. In this article, we perform numerical-relativity simulations of neutron-star mergers and investigate scenarios in which the onset density of such a phase transition is exceeded in at least one inspiralling binary component. Our simulations reveal that shortly before the merger it is possible that such stars undergo a "reverse phase transition", i.e., densities decrease and the quark core inside the star disappears leaving a purely hadronic star at merger. After the merger, when densities increase once more, the phase transition occurs again and leads, in the cases considered in this work, to a rapid formation of a black hole. We compute the gravitational-wave signal and the mass ejection for our simulations of such scenarios and find clear signatures that are related to the post-merger phase transition, e.g., smaller ejecta masses due to the softening of the equation of state through the quark core formation. Unfortunately, we do not find measurable imprints of the reverse phase transition.

Speed of sound in QCD matter at finite temperature and density

Speed of sound in QCD matter at finite temperature and density

Self-gravitating electrically charged anisotropic strange star model

The main focus of this paper is devoted to exploring the physical aspects of compact stars with the presence of electric charge under an embedded Class I approach in the arena of Bardeen geometry. We derive the embedded Class I solutions by taking spherically symmetric static spacetime with an anisotropic source of matter. We also look at the equation of state (EoS) for strange quark matter (SQM), which inspired the phenomenological MIT-Bag model as a free Fermi gas of quarks. The unknown constants are evaluated through the boundary conditions along with the Bardeen model to portray as an exterior space–time. Bardeen’s model becomes very interesting in an entertaining and unique way with great precision as it could be interpreted as the analytical solutions of some appropriate nonlinear electrodynamics associated with the gravitational field. In this concern, we thoroughly explored the dependence of several physical parameters, such as the metric potentials, energy density, pressure constituents, anisotropy, and electric charge, etc., on the chosen varied values of n. Finally, we discuss the physical viability and stability of the stellar model through various physical tests. It is important to mention here that the obtained stellar configuration is in agreement with the physical viability and stability criteria under the effect of the electric charge and anisotropic fluid source of matter.

Speed of sound and liquid-gas phase transition in nuclear matter

We investigate the speed of sound in nuclear matter at finite temperature and density (chemical potential) in the nonlinear Walecka model. The numerical results suggest that the behaviors of sound speed are closely related to the the nuclear liquid-gas (LG) phase transition and the associated spinodal structure. The adiabatic sound speed is nonzero at the critical endpoint (CEP) in the mean-field approximation. We further derive the boundary of vanishing sound velocity in the temperature-density phase diagram, and point out the region where the sound wave equation is broken. The distinction between the speed of sound in nuclear matter and that in quark matter contains important information about the equation of state of strongly interacting matter at intermediate and high density. We also formulate the relations between differently defined speeds of sound using the fundamental thermodynamic relations.

Cold dense quark matter for the Alcubierre drive model

The Alcubierre warp drive is a controversial theory by Miguel Alcubierre. Some arguments claim that it may not be physically possible. However, based on previous studies, this work suggests an extremely dense quark matter with a low-temperature limit of up to zero that can satisfy the requirements of the Alcubierre warp drive model considering the color interaction potential energy. The energy-momentum tensor and velocity of the warp drive model supported by the quark matter are also described.

Elliptic flow splitting of charged pions in relativistic heavy-ion collisions

Relativistic heavy-ion collisions are an important experimental way of studying the new state of matter as well as the phase diagram of the quantum chromodynamics (QCD) under extremely high temperatures and high densities. In recent years, the beam-energy scan program has been carried out on the relativistic heavy-ion collider at Brookhaven National Laboratory in USA, and the STAR collaboration at relativistic heavy ion collision (RHIC) has measured the difference in the elliptic flow <inline-formula><tex-math id="M5">\begin{document}$v_2$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M5.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M5.png"/></alternatives></inline-formula> between <inline-formula><tex-math id="M6">\begin{document}$\pi^-$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M6.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M6.png"/></alternatives></inline-formula> and <inline-formula><tex-math id="M7">\begin{document}$\pi^+$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M7.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M7.png"/></alternatives></inline-formula> on an event-by-event basis, and found a linear dependence on the charge asymmetry <i>A</i><sub>ch</sub> of the collision system, which is considered as a possible signal of the chiral magnetic wave. Based on the extended multi-phase transport model (AMPT), this paper uses a 3 flavor Nambu-Jona-Lasinio (NJL) model to study the quark isospin Mean-field potential, which provides a new idea for explaining the experimental phenomenon of the linear relationship between the pion elliptic flow splitting <inline-formula><tex-math id="M8">\begin{document}$\Delta v_2=v_2(\pi^-)- $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M8.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M8.png"/></alternatives></inline-formula><inline-formula><tex-math id="M8-1">\begin{document}$ v_2(\pi^+)$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M8-1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M8-1.png"/></alternatives></inline-formula> and charge asymmetry <i>A</i><sub>ch</sub>. Our results show that isovector interaction can cause a splitting of the isospin asymmetric quark matter mean-field potential, manifesting as <inline-formula><tex-math id="M9">\begin{document}$d(\bar{u})$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M9.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M9.png"/></alternatives></inline-formula> quarks experiencing a mean-field potential greater than <inline-formula><tex-math id="M10">\begin{document}$u(\bar{d})$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M10.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M10.png"/></alternatives></inline-formula> quarks. Therefore, <inline-formula><tex-math id="M11">\begin{document}$d(\bar{u})$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M11.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M11.png"/></alternatives></inline-formula> quarks experience more repulsion than <inline-formula><tex-math id="M12">\begin{document}$u(\bar{d})$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M12.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M12.png"/></alternatives></inline-formula> quarks in collision processes, resulting in a small increase in the elliptic flow of the partial subflow <inline-formula><tex-math id="M13">\begin{document}$v_2(d)$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M13.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M13.png"/></alternatives></inline-formula> and <inline-formula><tex-math id="M14">\begin{document}$v_2(\bar{u})$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M14.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M14.png"/></alternatives></inline-formula>, while <inline-formula><tex-math id="M15">\begin{document}$v_2(u)$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M15.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M15.png"/></alternatives></inline-formula> and <inline-formula><tex-math id="M16">\begin{document}$v_2(\bar{d})$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M16.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M16.png"/></alternatives></inline-formula> decrease slightly. In the hadronization process, the <inline-formula><tex-math id="M17">\begin{document}$\pi$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M17.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M17.png"/></alternatives></inline-formula> elliptic flow splitting occurs due to the split of <inline-formula><tex-math id="M18">\begin{document}$d$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M18.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M18.png"/></alternatives></inline-formula> and <inline-formula><tex-math id="M19">\begin{document}$u$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M19.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M19.png"/></alternatives></inline-formula> elliptic flows combined with the split of <inline-formula><tex-math id="M20">\begin{document}$\bar{u}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M20.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M20.png"/></alternatives></inline-formula> and <inline-formula><tex-math id="M21">\begin{document}$\bar{d}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M21.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M21.png"/></alternatives></inline-formula> elliptic flows. We also found a linear correlation between charge asymmetry and isospin asymmetry at mid-rapidity region from our transport model, and thus explained the experimental phenomenon of the linear relationship between the pion elliptic flow splitting <inline-formula><tex-math id="M22">\begin{document}$\Delta v_2$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M22.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M22.png"/></alternatives></inline-formula> and charge asymmetry <i>A</i><sub>ch</sub> by using the isospin mean-field potential of quark matter. Further, isospin properties of quark matter also provide a theoretical basis for isobar collisions and the equation of state of compact star matter.

Global polarization of hyperons and spin alignment of vector mesons in quark matters

<sec>Relativistic heavy ion collider (RHIC) as a dedicated nuclear facility has made a few major discoveries in physics. This year marks the 30th year STAR Collaboration formation and the 23th year of STAR detector operation and data collection at RHIC. In the last two decades, STAR has collected many datasets, exhibiting scientific versatility and flexibility of the RHIC facility. The total dataset in the first year is less than 1 million good events, and currently there are about 1 billion events per dataset.</sec><sec>The Global Hyperon Polarization was proposed in 2004. This immediately prompted the STAR Collaboration to search for this phenomenon from the early datasets. The null results were presented at Quark Matter Conference in Shanghai in 2006 and subsequently published. Although there were peripheral and continuous efforts in the following decade, no positive result has been observed experimentally. This situation changed in the following decade with the upgrade of high data rate and time-of-flight (TOF) detector and the progress of the Beam Energy Scan Phase I (BES-I). The experimental discoveries of the global polarization of hyperons in 2017 and the spin alignment of vector mesons in 2023 at RHIC-STAR confirm the theory which was established nearly twenty years ago. The theory and these measurements open the way to studying the properties of the hot and dense nuclear matter created in high-energy heavy ion collisions from a new degree of freedom, spin.</sec><sec>We briefly review these discoveries from the proposals of theory to the experimental measurements, and summarize the related measurements at the existing facilities and the theoretical explanations to the original proposal. The basic understanding and the original proposal are still valid and fundamental, that is, the angular momentum of system can transform into a spin effect observable in experiment. However, it appears that in each case a new model is needed to explain the new experimental observation. We need a more basic theory to help us unify all these spin related phenomena.</sec><sec>Over the past five years, STAR has successfully installed 3 new detectors and we have begun to see the physical analysis results from datasets with those new functions. What makes the STAR detector viable after 20 years of operation is its continuous evolution through successful upgrades, with new scientific programs added year by year. The next big thing is to forward upgrade a tracking system (3 layers of silicon strips and 4 layers of sTGC chambers) and a calorimetry system (electromagnetic and hadronic calorimeters). In addition to studying the spin structure of protons by using the polarized proton beams at RHIC, the upgrades also provide a unique ability to investigate the origin of Λ Global Polarization as a function of rapidity and rapidity (de-)correlations in Au+Au collisions.</sec>

Measurements of global polarization of QCD matter in heavy-ion collisions

The experimental data of the global polarization of Λ hyperon, ϕ and K<sup>*0</sup> vector mesons in high-energy heavy ion collision confirm the new phenomenon of global polarization of hot-dense QCD matter, which has attracted extensive attention from researchers and has become a new hot research direction in the frontier of high-energy nuclear physics. This paper reviews the recent global polarization measurements. We focus on the global polarization measurements of Λ hyperon and ϕ, K<sup>*0</sup> mesons, carried out by the solenoidal tracker detector (STAR) collaboration group at the Relativistic Heavy Ion Collider (RHIC) at its Phase I of Beam Energy Scan program, and extend to the global polarization measurements containing multiple strange quark particles, such as Ξ, Ω and the local polarization studies of Λ along the beam direction. In the paper, we also briefly comment on the measurements at higher energy from the large hadron collider (LHC) and at very low energy in HADES experiment. In the end of the paper, the physical information given by these experimental results is also briefly discussed.

Limits on the nuclearite flux using the ANTARES neutrino telescope

In this work, a search for nuclearites of strange quark matter by using nine years of ANTARES data taken in the period 2009–2017 is presented. The passage through matter of these particles is simulated taking into account a detailed description of the detector response to nuclearites and of the data acquisition conditions. A down-going flux of cosmic nuclearites with Galactic velocities (β = 10-3) was considered for this study. The mass threshold for detecting these particles at the detector level is 4 × 1013 GeV/c 2. Upper limits on the nuclearite flux for masses up to 1017 GeV/c 2 at the level of ∼ 5 × 10-17 cm-2 s-1 sr-1 are obtained. These are the first upper limits on nuclearites established with a neutrino telescope and the most stringent ever set for Galactic velocities.

Early Quark Deconfinement in Compact Star Astrophysics and Heavy-ion Collisions

Based on a recently developed relativistic density functional approach to color-superconducting quark matter and a novel quark-hadron transition construction which phenomenologically accounts for the effects of inhomogeneous pasta phases and quark-hadron continuity, we construct a class of hybrid equations of state applicable at the regimes typical for compact star astrophysics and heavy ion collisions. We outline that early quark deconfinement is a notable consequence of strong diquark pairing providing a good agreement with the observational data and driving the trajectories of the matter evolution during the supernovae explosions toward the regimes typical for the compact star mergers and heavy-ion collisions.

Spin-orbital coupling in strong interaction and global spin polarization

In non-central relativistic heavy ion collisions, the colliding nuclear system possesses a huge global orbital angular momentum in the direction opposite to the normal of the reaction plane. Due to the spin-orbit coupling in strong interaction, such a huge orbital angular momentum leads to a global spin polarization of the quark matter system produced in the collision process. The global polarization effect in high energy heavy ion collisions was first predicted theoretically and confirmed by STAR experiments at the Relativistic Heavy Ion Collider in Brookhaven National Laboratory. The discovery has attracted much attention to the study of spin effects in heavy ion collision and leads to a new direction in high energy heavy ion physics—Spin Physics in Heavy Ion Collisions. In this paper, we briefly review the original ideas, the calculation methods, the main results and recent theoretical developments in last years. First, we present a short discussion of the spin-orbit coupling which is an intrinsic property for a relativistic fermionic quantum system. Then we review how the global orbital angular momentum can be generated in non-central heavy ion collisions and how the global orbital angular momentum can be transferred to the local orbital angular momentum distribution in two limit model---Landan fireball model and Bjorken scaling model. After that, we review how we can describe the scattering process with initial local orbital angular momentum in the formalism of scattering cross section in impact parameter space and how we calculate the polarization of the quarks and antiquarks in quark gluon plasma produced in non-central heavy ion collisions after single or multiple scattering. We also give a brief review on how the global polarization can be predicted from the formalism of relativistic hydrodynamics with the generalized Cooper-Frye formula with spin. Finally, we discuss how the quark's polarization can be transferred to the final hadron's polarization. We focus on the hyperon's polarization and vector meson's spin alignment produced in heavy-ion collisions.

Anomalous enhancement of dilepton production due to soft modes in dense quark matter

We explore how the dilepton production rate is modified near the critical temperature of color superconductivity and QCD critical point by the soft modes inherently associated with the phase transitions of second-order. It is shown that the soft modes affect the photon self-energy significantly through so called the Aslamasov-Larkin, Maki-Thompson and density of states terms, which are known responsible for the paraconductivity in the metalic superconductivity, and cause an anomalous enhancement of the production rate in the low energy/momemtum region.