Search Results (24)

We formulate a covariant mechanical equilibrium condition for the quark–hadron mixed phase boundary in the presence of a magnetic-field-induced pressure anisotropy. Using the relativistic thin-shell formalism to describe the quark–hadron boundary, we interpret conservation of stress-energy across the interface as a set of generalized Young–Laplace conditions which characterize the geometry of the interface. In a comoving stationary frame, this provides a covariant description of mechanical equilibrium at the interface, which serves as a replacement for the scalar pressure-balance condition used in the isotropic Gibbs construction. Full article

We investigate BZT shocks and the QCD phase transition in the dense core of a cold quark star in beta equilibrium subject to the multicomponent van der Waals (MvdW) equation of state (EoS) as a model of internal structure. When this system is expressed in terms of multiple components, it can be used to explore the impact of a phase transition from a hadronic state to a quark plasma state with a complex clustering structure. The clustering can take the form of colored diquarks or triquarks and bound colorless meson, baryon, or hyperon states at the phase transition boundary. The resulting multicomponent EoS system is nonconvex, which can give rise to Bethe–Zel’dovich–Thompson (BZT) phase-changing shock waves. Using the BZT shock wave condition, we find constraints on the quark density and examine how this changes the tidal deformability of the compact core. These results are then combined with the TOV equations to find the resulting mass and radius relationship. These states are compared to recent astrophysical high-mass neutron star systems, which may provide evidence for a core that has undergone a quark gluon phase transition such as PSR 0943+10 or GW 190814. Full article

The World-Class University/Hanyang Project launched in Korea in 2008 led to what is now called the “pseudo-conformal model” that addresses dense compact star matter and is confronted in this short note with the presently available astrophysical observables, with focus on those from gravity waves. The predictions made nearly free of parameters by the model involving “topology change” remain more or less intact “un-torpedoed” by the data. Full article

Electromagnetic (EM) observations and gravitational wave (GW) measurements enable us to determine the mass and radius of neutron stars (NSs) and their tidal deformability, respectively. These parameters offer valuable insights into the properties of dense matter in NSs. In this study, the vector-interaction-enhanced bag model (vBag model) is employed to investigate strange and hybrid stars’ properties. The parameters of the vBag model are constrained using multi-messenger observations, revealing that strange stars are incompatible with current observations. In contrast, hybrid stars can exhibit a substantial mixed phase region and a thin hadronic shell. Furthermore, we present the frequencies and damping time of fundamental mode (f-mode) oscillations of hybrid stars and test their universal relations with compactness and tidal deformability. The findings indicate that the presence of mixed phase components leads to larger frequencies and shorter damping time of the f-mode oscillation of hybrid stars, and the softer equation of state (EoS) affects this behavior more significantly. The universal relations of hybrid stars in the vBag model can be described by fourth-order/seventh-order polynomials, which do not break the previous results. Full article

The study of the high-density equation of state (EOS) and the search for a possible phase transition in dense baryonic matter is the main goal of beam energy scan programs with relativistic heavy ions at energies $\sqrt{s_{NN}}$= 2–5 GeV. The most stringent constraints currently available on the high-density EOS of symmetric nuclear matter come from the present measurements of directed ($v_1$) and elliptic flow ($v_2$) signals of protons in Au + Au collisions. In this energy range, the anisotropic flow is strongly affected by the presence of cold spectators due to the sizable passage time. The system size dependence of anisotropic flow may help to study the participant–spectator contribution and improve our knowledge of the EOS of symmetric nuclear matter. In this work, we discuss the layout of the upgraded BM@N experiment and the anticipated performance for differential anisotropic flow measurements of identified hadrons at Nuclotron energies: $\sqrt{s_{NN}}$= 2.3–3.5 GeV. Full article

We study radial oscillations in non-rotating neutron stars by considering the unified equation of states (EoSs), which support the 2 M_⊙ star criterion. We solve the Sturm–Liouville problem to compute the 20 lowest radial oscillation modes and their eigenfunctions for a neutron star modeled with eight selected unified EoSs from distinct Skyrme–Hartree–Fock, relativistic mean field and quarkyonic models. We compare the behavior of the computed eigenfrequency for an NS modeled with hadronic to one with quarkyonic EoSs while varying the central densities. The lowest-order f-mode frequency varies substantially between the two classes of the EoS at 1.4 M_⊙ but vanishes at their respective maximum masses, consistent with the stability criterion $\partial M/\partial {\rho }_c>0$. Moreover, we also compute large frequency separation and discover that higher-order mode frequencies are significantly reduced by incorporating a crust in the EoS. Full article

The description of the stellar interior of compact stars remains as a big challenge for the nuclear astrophysics community. The consolidated knowledge is restricted to density regions around the saturation of hadronic matter ${\rho }_0=2.8\times {10}^{14}\mathrm{g}{\mathrm{cm}}^{-3}$, regimes where our nuclear models are successfully applied. As one moves towards higher densities and extreme conditions up to the quark/gluons deconfinement, little can be said about the microphysics of the equation of state (EoS). Here, we employ a Markov Chain Monte Carlo (MCMC) strategy to access the variability at high density regions of polytropic piecewise models for neutron star (NS) EoS or possible hybrid stars, i.e., a NS with a small quark-matter core. With a fixed description of the hadronic matter for low density, below the nuclear saturation density, we explore a variety of models for the high density regimes leading to stellar masses near to $2.5M_{\odot }$, in accordance with the observations of massive pulsars. The models are constrained, including the observation of the merger of neutrons stars from VIRGO-LIGO and with the pulsar observed by NICER. In addition, we also discuss the possibility of the use of a Bayesian power regression model with heteroscedastic error. The set of EoS from the Laser Interferometer Gravitational-Wave Observatory (LIGO) was used as input and treated as the data set for the testing case. Full article

The anisotropic flow is one of the important observables sensitive to the equation of state (EOS) and transport properties of the strongly interacting matter created in relativistic heavy-ion collisions. In this work, we report a detailed multi-differential study of the directed ($v_1$), elliptic ($v_2$), triangular ($v_3$), and quadrangular ($v_4$) flow coefficients of protons in relativistic heavy-ion collisions at $\sqrt{s_{NN}}$ = 2.2–4.5 GeV using several hadronic transport models. Recent published results for Au + Au collisions at $\sqrt{s_{NN}}$ = 2.4 GeV from HADES experiment and at $\sqrt{s_{NN}}$ = 3.0 GeV from the STAR experiment have been used for comparison. The study motivates further experimental investigations of the anisotropic collective flow of protons and neutrons in a high baryon density region. Full article

We generalize a recently proposed confining relativistic density-functional approach to the case of density-dependent vector and diquark couplings. The particular behavior of these couplings is motivated by the non-perturbative gluon exchange in dense quark matter and provides the conformal limit at asymptotically high densities. We demonstrate that this feature of the quark matter EoS is consistent with a significant stiffness in the density range typical for the interiors of neutron stars. In order to model these astrophysical objects, we construct a family of hybrid quark-hadron EoSs of cold stellar matter. We also confront our approach with the observational constraints on the mass–radius relation of neutron stars and their tidal deformabilities and argue in favor of a quark matter onset at masses below $1.0{\mathrm{M}}_{\odot }$. Full article

High-energy heavy-ion collisions offer the unique possibility to study fundamental properties of nuclear matter in the laboratory, which are relevant for our understanding of the structure of compact stellar objects and the dynamics of neutron star mergers. Of particular interest are the nuclear matter equation of state (EOS), the in-medium modifications of hadrons and the degrees of freedom of matter at high densities and temperatures. Pioneering experiments exploring the EOS for symmetric matter were performed at the SIS18 accelerator of GSI, measuring, as function of beam energy, the collective flow of protons and of light fragments and subthreshold strangeness production. These data were reproduced by various microscopic transport model calculations, providing, up to date, the best constraint for the EOS of symmetric matter with an incompressibility of about 200 MeV for densities up to twice the saturation density. This article reviews the experimental results on subthreshold kaon production together with the theoretical interpretation and gives a brief outlook towards future experiments at higher densities. Full article

Neutron star is an important object for us to verify the equation of state of hadronic matter. For a specific choice of equations of state, mass and radius of a neutron star are determined, for which there are constraints from observations. According to some previous studies, since the strong magnetic field acts as a repulsive force, there is a possibility that neutron stars with strong magnetic fields may have relatively heavier masses than other non-magnetized neutron stars. In this paper, the structure of a neutron star with a strong internal magnetic field is investigated by changing its internal functional form to see how much the neutron star can be massive and also how radius of a neutron star can be within a certain range. Full article

I discuss how the axial current coupling constant $g_A$ renormalized in scale symmetric chiral EFT defined at a chiral matching scale impacts on the axial current matrix elements on beta decays in nuclei with and without neutrinos. The “quenched” $g_A$ observed in nuclear superallowed Gamow–Teller transitions, a long-standing puzzle in nuclear physics, is shown to encode the emergence of chiral-scale symmetry hidden in QCD in the vacuum. This enables one to explore how trace-anomaly-induced scale symmetry breaking enters in the renormalized $g_A$ in nuclei applicable to certain non-unique forbidden processes involved in neutrinoless double beta decays. A parallel is made between the roles of chiral-scale symmetry in quenching $g_A$ in highly dense medium and in hadron–quark continuity in the EoS of dense matter in massive compact stars. A systematic chiral-scale EFT, presently lacking in nuclear theory and potentially crucial for the future progress, is suggested as a challenge in the field. Full article

The density dependence of nuclear symmetry energy is among the most uncertain parts of the Equation of State (EOS) of dense neutron-rich nuclear matter. It is currently poorly known especially at suprasaturation densities partially because of our poor knowledge about isovector nuclear interactions at short distances. Because of its broad impacts on many interesting issues, pinning down the density dependence of nuclear symmetry energy has been a longstanding and shared goal of both astrophysics and nuclear physics. New observational data of neutron stars including their masses, radii, and tidal deformations since GW170817 have helped improve our knowledge about nuclear symmetry energy, especially at high densities. Based on various model analyses of these new data by many people in the nuclear astrophysics community, while our brief review might be incomplete and biased unintentionally, we learned in particular the following: (1) The slope parameter L of nuclear symmetry energy at saturation density ${\rho }_0$ of nuclear matter from 24 new analyses of neutron star observables was about $L\approx 57.7\pm 19$ MeV at a 68% confidence level, consistent with its fiducial value from surveys of over 50 earlier analyses of both terrestrial and astrophysical data within error bars. (2) The curvature $K_{\mathrm{sym}}$ of nuclear symmetry energy at ${\rho }_0$ from 16 new analyses of neutron star observables was about $K_{\mathrm{sym}}\approx -107\pm 88$ MeV at a 68% confidence level, in very good agreement with the systematics of earlier analyses. (3) The magnitude of nuclear symmetry energy at $2{\rho }_0$, i.e., $E_{\mathrm{sym}}\left(2{\rho }_0\right)\approx 51\pm 13$ MeV at a 68% confidence level, was extracted from nine new analyses of neutron star observables, consistent with the results from earlier analyses of heavy-ion reactions and the latest predictions of the state-of-the-art nuclear many-body theories. (4) While the available data from canonical neutron stars did not provide tight constraints on nuclear symmetry energy at densities above about $2{\rho }_0$, the lower radius boundary $R_{2.01}=12.2$ km from NICER’s very recent observation of PSR J0740+6620 of mass $2.08\pm 0.07$$M_{\odot }$ and radius $R=12.2–16.3$ km at a 68% confidence level set a tight lower limit for nuclear symmetry energy at densities above $2{\rho }_0$. (5) Bayesian inferences of nuclear symmetry energy using models encapsulating a first-order hadron–quark phase transition from observables of canonical neutron stars indicated that the phase transition shifted appreciably both L and $K_{\mathrm{sym}}$ to higher values, but with larger uncertainties compared to analyses assuming no such phase transition. (6) The high-density behavior of nuclear symmetry energy significantly affected the minimum frequency necessary to rotationally support GW190814’s secondary component of mass (2.50–2.67) $M_{\odot }$ as the fastest and most massive pulsar discovered so far. Overall, thanks to the hard work of many people in the astrophysics and nuclear physics community, new data of neutron star observations since the discovery of GW170817 have significantly enriched our knowledge about the symmetry energy of dense neutron-rich nuclear matter. Full article

The poorly known properties of high-density strongly-interacting matter govern the structure of neutron stars and the dynamics of neutron star mergers. New insight has been and will be gained by astronomical observations, such as the measurement of mass and radius of neutron stars, and the detection of gravitational waves emitted from neutron star mergers. Alternatively, information on the Nuclear Matter Equation-of-State (EOS) and on a possible phase transition from hadronic to quark matter at high baryon densities can be obtained from laboratory experiments investigating heavy-ion collisions. Detector systems dedicated to such experiments are under construction at the “Facility for Antiproton and Ion Research” (FAIR) in Darmstadt, Germany, and at the “Nuclotron-based Ion Collider fAcility” (NICA) in Dubna, Russia. In heavy-ion collisions at these accelerator centers, one expects the creation of baryon densities of up to 10 times saturation density, where quark degrees-of-freedom should emerge. This article reviews the most promising observables in heavy-ion collisions, which are used to probe the high-density EOS and possible phase transition from hadronic to quark matter. Finally, the facilities and the experimental setups will be briefly described. Full article

Based on recent perturbative and non-perturbative lattice calculations with almost quark flavors and the thermal contributions from photons, neutrinos, leptons, electroweak particles, and scalar Higgs bosons, various thermodynamic quantities, at vanishing net-baryon densities, such as pressure, energy density, bulk viscosity, relaxation time, and temperature have been calculated up to the TeV-scale, i.e., covering hadron, QGP, and electroweak (EW) phases in the early Universe. This remarkable progress motivated the present study to determine the possible influence of the bulk viscosity in the early Universe and to understand how this would vary from epoch to epoch. We have taken into consideration first- (Eckart) and second-order (Israel–Stewart) theories for the relativistic cosmic fluid and integrated viscous equations of state in Friedmann equations. Nonlinear nonhomogeneous differential equations are obtained as analytical solutions. For Israel–Stewart, the differential equations are very sophisticated to be solved. They are outlined here as road-maps for future studies. For Eckart theory, the only possible solution is the functionality, $H\left(a\right(t\left)\right)$, where $H\left(t\right)$ is the Hubble parameter and $a\left(t\right)$ is the scale factor, but none of them so far could to be directly expressed in terms of either proper or cosmic time t. For Eckart-type viscous background, especially at finite cosmological constant, non-singular $H\left(t\right)$ and $a\left(t\right)$ are obtained, where $H\left(t\right)$ diverges for QCD/EW and asymptotic EoS. For non-viscous background, the dependence of $H\left(a\right(t\left)\right)$ is monotonic. The same conclusion can be drawn for an ideal EoS. We also conclude that the rate of decreasing $H\left(a\right(t\left)\right)$ with increasing $a\left(t\right)$ varies from epoch to epoch, at vanishing and finite cosmological constant. These results obviously help in improving our understanding of the nucleosynthesis and the cosmological large-scale structure. Full article