The recent measurements of the masses of the pulsar J00737-3039B and of the companion J1756-2251 and pulsars PSR J1614-2230, PSR J0348-0432 demonstrate the existence of compact stars with masses in a broad range from 1.2 to 2 $M_\odot$. To fulfill the constraint $M_{\rm max}>2M_{\odot}$ and to demonstrate the possibility of cooling scenarios for purely hadronic and further for hybrid stars we exploit the stiff DD2 hadronic equation of state producing a maximum neutron star mass $M\simeq 2.43 M_{\odot}$. We show that the "nuclear medium cooling" scenario for neutron stars comfortably explains the whole set of cooling curves just by a variation of the star masses without the necessity for the occurrence of the direct Urca reaction. To describe the cooling data with the very stiff DD2 equation of state we select a proton gap profile from those exploited in the literature and allow for a variation of the effective pion gap controlling the efficiency of the medium modified Urca process. Fast cooling of young neutron stars like it is seen in the data for Cas A is explained with the DD2 equation of state when the following conditions are provided: the presence of an efficient medium modified Urca process, and a large proton gap at densities $n\le 2n_0$ vanishing for $n\ge (2.5 - 3) n_0$, where $n_0$ is the saturation nuclear density.
We present in this paper a simple and unequivocal prediction on the deformation of the compact star, that will be measured in gravity waves, with an EoS obtained in renormailzation-group implemented effective field theory anchored on scale and hidden-local symmetric Lagrangian endowed with topology change . The objective is not to offer a superior or improved EoS for compact stars but to confront with a forthcoming astrophysical observable the given model formulated in what is considered to be consistent with the premise of QCD. The model so obtained is found to satisfactorily describe the obs…
Recent evidence for high masses ($\sim 2~ M_\odot$) pulsars PSR J1614-2230 and PSR J0348-0432 requires neutron star matter to have a stiff equation of state (EoS). The thermal evolution of compact stars (CS) with stiff hadronic EoS necessitates the application of the "nuclear medium cooling" scenario with a selection of appropriate proton gap profiles together with in-medium effects (like pion softening) on cooling mechanisms in order to achieve a satisfactory explanation of all existing observational data for the temperature-age relation of CS. Here we focus on two examples from \cite{Grigori…
An EOS-Driven Extension of NSCool for Compact Star Cooling with Hadronic and Quark Degrees of Freedom
Università degli Studi della Campania “Luigi Vanvitelli”（坎帕尼亚路易吉范维特利大学）；Istituto Nazionale di Fisica Nucleare, Sezione di Napoli（意大利国家核物理研究所那不勒斯分部）；Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Frascati（意大利国家核物理研究所弗拉斯卡蒂国家实验室）；Universidad Rey Juan Carlos（胡安卡洛斯国王大学）
The existence of high mass ($\sim 2M_{\odot}$) pulsars PSR J1614-2230 and PSR J0348-0432 requires the compact star matter to be described by a stiff equation of state (EoS). Presence of hyperons in neutron stars leads to a softening of the EoS that results in a decrease of the maximum neutron-star mass below the measured values of masses for PSR J1614-2230 and PSR J0348-0432 pulsars if one exploits ordinary relativistic mean-field (RMF) models (hyperon puzzle). However, within an RMF EoS with a sigma-scaled hadron effective masses and coupling constants, the maximum neutron-star mass remains a…
We construct an equation of state (EOS) for neutron stars by interpolating hadronic EOS at low density and quark EOS at high density. A hadronic model based on the parity doublet structure is used for hadronic matter and a quark model of Nambu--Jona-Lasinio type is for quark matter. We assume crossover between hadronic matter and quark matter in the the color-flavor locked phase. The nucleon mass of the parity doublet model has a mass associated with the chiral symmetry breaking, and a chiral invariant mass $m_0$ which is insensitive to the chiral condensate. The value of $m_0$ affects the nuc…
We revisit Bondi accretion - steady-state, adiabatic, spherical gas flow onto a Schwarzschild black hole at rest in an asymptotically homogeneous medium - for stiff polytropic equations of state (EOSs) with adiabatic indices $Γ> 5/3$. A general relativistic treatment is required to determine their accretion rates, for which we provide exact expressions. We discuss several qualitative differences between results for soft and stiff EOSs - including the appearance of a minimum steady-state accretion rate for EOSs with $Γ\geq 5/3$ - and explore limiting cases in order to examine these differences.…
Within the "nuclear medium cooling" scenario of neutron stars all reliably known temperature - age data, including those of the central compact objects in the supernova remnants of Cassiopeia A and XMMU-J1732, can be comfortably explained by a set of cooling curves obtained by variation of the star mass within the range of typical observed masses. The recent measurements of the high masses of the pulsars PSR J1614-2230 and PSR J0348-0432 on the one hand, and of the low masses for PSR J0737-3039B and the companion of PSR J1756-2251 on the other, provide independent proof for the existence of ne…
We explore the connection between the stiffness of an hadronic equation of state (EoS) with a sharp phase transition to quark matter to its tidal deformability. For this we employ a hadronic relativistic mean field model with a parameterized effective nucleon mass to vary the stiffness in conjunction with a constant speed of sound EoS for quark matter. We compute multiple scenarios with phase transitions according to the four possible cases of a hybrid star EoS with a stable second branch. We demonstrate at the example of GW170817 how the effective nucleon mass can be constrained by using grav…
Measurements demonstrate the existence of compact stars with masses in a broad range from 1.2 to 2 $M_\odot$. The most massive of these objects might be hybrid stars. To fulfill the constraint $M_{\rm max}>2~M_{\odot}$ with a reserve we exploit the stiff DD2 hadronic equation of state (EoS) without and with excluded volume (DD2vex) correction, which produce maximum neutron star masses of $M_{\rm max} = 2.43~M_{\odot}$ and $2.70~M_{\odot}$, respectively. We show that the stiffness of the EoS does not preclude an explanation of the whole set of cooling data within "nuclear medium cooling" scenar…
Neutron stars are commonly considered as astronomical objects having highdensity interiors and an inner core region in which various hadronic matter phases are expected. Several studies show that the inner structures affect macroscopic phenomena of the star. However, we know that the inner structures of the star strongly depend on the equation of state (EOS). The EOS of high-density matter is still not clear and several recent observations indicate restrictions to EOSs. Theoretical studies should elucidate EOSs at high density and/or high temperature. For instance, many theoretical studies hav…
We analyze the recent astrophysical constraints in the context of a hadronic equation of state (EoS), in which the baryonic matter is subject to chiral symmetry restoration. We show that with such EoS it is possible to reconcile the modern constraints on the neutron star (NS) mass, radius, and tidal deformability (TD). We find that the softening of the EoS, required by the TD constraint of a canonical $1.4~M_\odot$ NS, followed by a subsequent stiffening, required by the $2~M_\odot$ constraint, is driven by the appearance of $Δ$ matter due to partial restoration of chiral symmetry. Consequentl…
The last few years have seen tremendous progress in the observation of the global properties of neutron stars (NSs), e.g. masses, radii and tidal deformabilities. Such properties provide information about possible phase transitions in the inner cores of NSs, provided the connection between observed masses and radii and the equation of state (EoS) is well understood. We focus the present study on first-order phase transitions, which often softens the EoS and consequently reduces the maximum mass as well as the radii of NSs. Here, we challenge this conventional expectation by constructing explic…
Fully general-relativistic binary-neutron-star (BNS) merger simulations with quark-hadron crossover (QHC) equations of state (EOSs) are studied for the first time. In contrast to EOSs with purely hadronic matter or with a first-order quark-hadron phase transition (1PT), in the transition region QHC EOSs show a peak in sound speed, and thus a stiffening. We study the effects of such stiffening in the merger and post-merger gravitational (GW) signals. Through simulations in the binary-mass range $2.5 < M/M_{\odot} < 2.75$, characteristic differences due to different EOSs appear in the frequency …
Discovery of huge magnetic field in magnetars has stimulated a renewed interest about the magnetic field and physics of compact stars, where microphysics such as QED or QCD may play active parts. Here we discuss the equation of state (EOS) of quark matter in the core of compact stars by taking into account the strong magnetic field. We show that quark EOS becomes very stiff in the presence of the strong magnetic field, and becomes stiffest under the causality condition beyond the threshold strength of $B_c\sim O(10^{19})$ G. This is because quarks make the Landau levels in the presence of the …
The recent observation of the pulsar PSR J1614-2230 with a mass of 1.97 +/- 0.04 M_sun gives a strong constraint on the quark and nuclear matter equations of state (EoS). We explore the parameter ranges for a parameterized EoS for quark stars. We find that strange stars, made of absolutely stable strange quark matter, comply with the new constraint only if effects from the strong coupling constant and color-superconductivity are taken into account. Hybrid stars, compact stars with a quark matter core and an hadronic outer layer, can be as massive as 2 M_sun, but only for a significantly limite…
We aim at contributing to the resolution of three of the fundamental puzzles related to the still unsolved problem of the structure of the dense core of compact stars (CS): (i) the hyperon puzzle: how to reconcile pulsar masses of $2\,$M$_\odot$ with the hyperon softening of the equation of state (EoS); (ii) the masquerade problem: modern EoS for cold, high density hadronic and quark matter are almost identical; and (iii) the reconfinement puzzle: what to do when after a deconfinement transition the hadronic EoS becomes favorable again? We show that taking into account the compositeness of bar…
We explore systematically a new class of two-phase equations of state (EoS) for hybrid stars that is characterized by three main features : (1) stiffening of the nuclear EoS at supersaturation densities due to quark exchange effects (Pauli blocking) between hadrons, modelled by an excluded volume correction, (2) stiffening of the quark matter EoS at high densities due to multiquark interactions and (3) possibility for a strong first order phase transition with an early onset and large density jump. The third feature results from a Maxwell construction for the possible transition from the nucle…
A two-phase description of the quark-nuclear matter hybrid equation of state that takes into account the effect of excluded volume in both the hadronic and the quark matter phases is introduced. The nuclear phase manifests a reduction of the available volume as density increases, leading to a stiffening of the matter. The quark matter phase displays a reduction of the effective string tension in the confining density functional from available volume contributions. The nuclear equation of state is based upon the relativistic density functional model DD2 with excluded volume. The quark matter is…
We introduce a family of equations of state (EoS) for hybrid neutron star (NS) matter that is obtained by a two-zone parabolic interpolation between a soft hadronic EoS at low densities and a stiff quark matter EoS with color superconductivity at high densities within a finite region of baryonic chemical potentials $μ_B^h < μ_B < μ_B^q$. We consider two scenarios corresponding to a cross-over and a strong first-order transition between quark and hadron phases considered at finite and zero temperatures. This allows us to analyze the effects of finite entropy on the EoS and mass-radius relation …
On the basis of the percolation picture from the hadronic phase with hyperons to the quark phase with strangeness, we construct a new equation of state (EOS) with the pressure interpolated as a function of the baryon density. The maximum mass of neutron stars can exceed $2M_{\odot}$ if the following two conditions are satisfied; (i) the crossover from the hadronic matter to the quark matter takes place at around three times the normal nuclear matter density, and (ii) the quark matter is strongly interacting in the crossover region and has stiff equation of state. This is in contrast to the con…
We introduce a family of equations of state (EoS) for hybrid neutron star (NS) matter that is obtained by a two-zone parabolic interpolation between a soft hadronic EoS at low densities and a set of stiff quark matter EoS at high densities within a finite region of chemical potentials $μ_H < μ< μ_Q$. Fixing the hadronic EoS as the APR one and choosing the color-superconducting, nonlocal NJL model with two free parameters for the quark phase, we perform Bayesian analyses with this two-parameter family of hybrid EoS. Using three different sets of observational constraints that include the mass o…
We show the existence and investigate the location of the special point (SP) in which hybrid neutron star mass-radius (M-R) curves have to cross each other when they belong to a class of hybrid equation of state (EoS) constructed with generic constant--speed--of--sound (CSS) quark matter models for which the onset deconfinement is varied. We demonstrate that for a three-parameter CSS model the position of the SP in the M-R diagram is largely independent of the choice of the hadronic EoS, but in dependence on the stiffness of the quark matter EoS it spans a region that we identify. We find that…
Analysis of directed flow ($v_1$) of protons, antiprotons and pions in heavy-ion collisions is performed in the range of collision energies $\sqrt{s_{NN}}$ = 2.7--39 GeV. Simulations have been done within a three-fluid model employing a purely hadronic equation of state (EoS) and two versions of the EoS with deconfinement transitions: a first-order phase transition and a smooth crossover transition. The crossover EoS is unambiguously preferable for the description of experimental data at lower collision energies $\sqrt{s_{NN}}\leq$ 20 GeV. However, at higher collision energies $\sqrt{s_{NN}}\g…
We consider the possibility of having hybrid stars with a phase transition from hadrons into strange matter at the core of a neutron star in b equilibrium. For the hadron phase equation of state (EoS) the quark-meson coupling model is used, while the MIT bag model is used to describe the strange matter phase. The phase transition is treated using the Gibbs construction method and results are calculated and checked against the observational constaints imposed on the EoS. The results are also compared with the hadronic EoS including hyperons, F-QMC700
Nonperturbative equations of state (EoSs) for two and three quark flavors are constructed with the functional renormalization group (FRG) within a quark-meson model truncation augmented by vector mesons for low temperature and high density. Based on previous FRG studies without repulsive vector meson interactions the influence of isoscalar vector $ω$- and $ϕ$-mesons on the dynamical fluctuations of quarks and (pseudo)scalar mesons is investigated. The grand potential as well as vector meson condensates are evaluated as a function of quark chemical potential and the quark matter EoS in $β$-equi…
In this contribution, we outline a new 2-phase description of the quark-nuclear matter hybrid equation of state that takes into account effects of phase space occupation (excluded volume) in both, the hadronic and the quark matter phases. For the nuclear matter phase, the reduction of the available volume at increasing density leads to a stiffening, while for the quark matter phase a reduction of the effective string tension in the confining density functional is obtained. The deconfinement phase transition in the resulting hybrid equation of state is sensitive to both excluded volume effects.…
The description of stellar interior remains as a big challenge for the nuclear astrophysics community. The consolidated knowledge is restricted to density regions around the saturation of hadronic matter $ρ_{0} = 2.8\times 10^{14} {\rm\ g\ cm^{-3}}$, regimes where our nuclear models are successfully applied. As one moves towards higher densities and extreme conditions up to five to twenty times $ρ_{0}$, little can be said about the microphysics of such objects. Here, we employ a Markov Chain Monte Carlo (MCMC) strategy to access the variability of polytropic three-pircewised models for neutron…
We have studied the effect of tidal deformability constraint given by the binary neutron star merger event GW170817 on the equations of state (EOS) of hybrid stars. The EOS are constructed by matching the hadronic EOS described by relativistic mean field (RMF) model and parameter sets NL3, TM1 and NL3$ωρ$ with the quark matter EOS described by modified MIT bag model, via Gibbs' construction. It is found that the tidal deformability constraints along with the lower bound on maximum mass ($M_{\rm max}=2.01\pm0.04M_\odot$) significantly limit the bag model parameter space ($B_{\rm eff}^{1/4}$, $a…
Pure hadronic compact stars, above a limiting value ($\approx$1.6 M$_\odot$) of their gravitational masses, to which predictions of most of other equations of state (EoSs) are restricted, can be reached from the equation of state (EoS) obtained using DDM3Y effective interaction. This effective interaction is found to be quite successful in providing unified description of elastic and inelastic scattering, various radioactivities and nuclear matter properties. We present a systematic study of the properties of pure hadronic compact stars. The $β$-equilibrated neutron star matter using this EoS …
We investigate the equation of state(EoS) and the effect of the hadron-quark phase transition of strong interaction matter in compact stars. The hadron matter is described with the relativistic mean field theory,and the quark matter is described with the Dyson-Schwinger equation approach of QCD. The complete EoS of the hybrid star matter is constructed with not only the Gibbs construction but also the 3-window interpolation. The mass-radius relation of hybrid stars is also investigated. We find that, although the EoSs of both the hadron matter with hyperon and $Δ$-baryon and the quark matter a…
We compute the mass, radius and tidal deformability of stars containing phase transitions from hadronic to quark phase(s). These quantities are computed for three types of hadronic envelopes: purely nuclear, hyperonic, and $Δ$-resonance--hyperon admixed matter. We consider either a single first-order phase transition to a quark phase with a maximally stiff equation of state (EOS) or two sequential first-order phase transitions mimicking a transition from hadronic to a quark matter phase followed by a second phase transition to another quark phase. We explore the parameter space which produces …
The quark-meson model is investigated for the two- and three-flavor case extended by contributions of vector mesons under conditions encountered in core-collapse supernova matter. Typical temperature ranges, densities and electron fractions, as found in core-collapse supernova simulations, are studied by implementing charge neutrality and local beta-equilibrium with respect to weak interactions. Within this framework, we analyze the resulting phase diagram and equation of state (EoS) and investigate the impact of undetermined parameters of the model. The EoS turns out to be relatively independ…
We study transitions of hadronic matter (HM) to 3-flavor quark matter (3QM), regarding the conversion processes as combustion and describing them hydrodynamically. Under the assumption that HM is metastable with their free energies being larger than those of 3QM but smaller than those of 2-flavor quark matter (2QM), we consider in this paper the conversion induced by diffusions of seed 3QM. This is a sequel to our previous paper, in which the shock-induced conversion was studied in the same frame work. We not only pay attention to the jump condition on both sides of the conversion front but th…
Is The Trace Anomaly at its Minimum Value at Neutron Star Centers?
Key Laboratory of Nuclear Physics and Ion-beam Application (MOE), Institute of Modern Physics, Fudan University（复旦大学现代物理研究所）；Shanghai Research Center for Theoretical Nuclear Physics, NSFC and Fudan University（复旦大学理论核物理上海研究中心）；Department of Physics and Astronomy, East Texas A&M University（东德克萨斯农工大学物理与天文系）
INFN, Sezione di Milano Bicocca（意大利国家核物理研究所米兰比可卡分部）；Università di Ferrara（费拉拉大学）；Università di Pisa（比萨大学）；INFN, Sezione di Pisa（意大利国家核物理研究所比萨分部）；Theoretisch-Physikalisches Institut, Friedrich-Schiller-Universität Jena（耶拿弗里德里希·席勒大学理论物理研究所）；Dipartimento di Fisica, Università di Trento（特伦托大学物理系）；INFN-TIFPA, Trento Institute for Fundamental Physics and Applications（意大利国家核物理研究所-特伦托基础物理与应用研究所）；Institute for Gravitation and the Cosmos, The Pennsylvania State University（宾夕法尼亚州立大学引力与宇宙学研究所）；Department of Physics, The Pennsylvania State University（宾夕法尼亚州立大学物理系）；Department of AStronomy & Astrophysics, The Pennsylvania State University（宾夕法尼亚州立大学天文学与天体物理学系）
We perform a Bayesian analysis in the basis of a recently developed two-parameter class of hybrid equations of state that allow for high-mass compact star twins. While recently a wide range of radii, from 9 - 15 km, has been inferred for different neutron stars using different techniques, we perform our analysis under the supposition that the radii are towards the large end ($13-15$ km). We use this radius constraint together with the undebated statistically independent constraint for high masses ($\sim 2~M_\odot$) as priors in selecting the most probable hybrid equations of state from a famil…
Properties of neutron stars in GW170817 are investigated using different equations of state (EoS) involving nucleons, $Λ$ hyperons, quarks resulting in $2M_{\odot}$ neutron stars. This calculation is performed using the same EoS for merger components and for low spin prior case. It is found from the computations of tidal deformability parameters that soft to moderately stiff equations of state are allowed by the 50$\%$ and 90$\%$ credible regions obtained from the gravitational wave observation of binary neutron star merger GW170817, whereas the stiffest hadron-quark EoS which lies above the u…
A principal goal of gravitational-wave astronomy is to constrain the neutron star equation of state (EOS) by measuring the tidal deformability of neutron stars. The tidally induced departure of the waveform from that of point-particle (or spinless binary black hole (BBH)) increases with the stiffness of the EOS. We show that causality (the requirement that the speed of sound is less than the speed of light for a perfect fluid satisfying a one-parameter equation of state) places an upper bound on tidal deformability as a function of mass. Like the upper mass limit, the limit on deformabity is o…
We show that the odds of the mass-gap (secondary) object in GW190814 being a neutron star (NS) improve if one allows for a stiff high-density equation of state (EoS) or a large spin. Since its mass is $\in (2.50,2.67) M_{\odot}$, establishing its true nature will make it either the heaviest NS or the lightest black hole (BH), and can have far-reaching implications on NS EoS and compact object formation channels. When limiting oneself to the NS hypothesis, we deduce the secondary's properties by using a Bayesian framework with a hybrid EoS formulation that employs a parabolic expansion-based nu…
Nonlocal PNJL models allow for a detailed description of chiral quark dynamics with running quark masses and wave function renormalization in accordance with lattice QCD (LQCD) in vacuum. Their generalization to finite temperature T and chemical potential μ allows to reproduce the μ-dependence of the pseudocritical temperature from LQCD when a nonvanishing vector meson coupling is adjusted. This restricts the region for the critical endpoint in the QCD phase diagram and stiffens the quark matter equation of state (EoS). It is demonstrated that the construction of a hybrid EoS for compact star …
We studied thermal evolution of isolated neutron stars (NSs) including the pion condensation core, with an emphasis on the stiffness of equation of state (EOS). Many temperature observations can be explained by the minimal cooling scenario which excludes the fast neutrino cooling process. However, several NSs are cold enough to require it. The most crucial problem for NS cooling theory is whether the nucleon direct Urca (DU) process is open. The DU process is forbidden if the nucleon symmetry energy is significantly low. Hence, another fast cooling process is required in such an EOS. As the ca…
Hyperon ($Y$) mixing in neutron-star matter brings about a remarkable softening of the equation of state (EoS) and the maximum mass is reduced to a value far less than $2M_{\odot}$. One idea to avoid this "hyperon puzzle in neutron stars" is to assume that the many-body repulsions work universally for every kind of baryons. The other is to take into account the quark deconfinement phase transitions from a hadronic EoS to a sufficiently stiff quark-matter EoS. In the present approach, both effects are handled in a common framework. As well as the hadronic matter, the quark matter with the two-b…
In this article the role of the supersaturation density equation of state (EOS) is explored in simulations of failed core-collapse supernova explosions. Therefore the nuclear EOS is extended via a one-parameter excluded volume description for baryons, taking into account their finite and increasing volume with increasing density in excess of saturation density. Parameters are selected such that the resulting supernova EOS represent extreme cases, with high pressure variations at supersaturation density which feature extreme stiff and soft EOS variants of the reference case, i.e. without exclud…
We investigate the effect of feeble interaction of dark matter (DM) with hadronic matter on the equation of state (EoS) and structural properties of neutron stars (NSs) in static conditions. For the purpose we adopt the effective chiral model for the hadronic sector and for the first time in the context of possible existence of DM inside NSs, we introduce DM-SM interaction through light new physics mediator. Moreover, the mass of DM fermion, the mediator and the coupling are adopted from the self-interaction constraint from Bullet cluster and from present day relic abundance. Within the consid…
