Showing papers on "Quark star published in 2001"
TL;DR: In this paper, the authors consider propagation of heavy quarks in QCD matter and show that the radiative quark energy loss appears to be qualitatively different from that of light quarks at all energies of practical importance.
738 citations
01 Jan 2001
TL;DR: In this paper, the Tensor Virial Method and its applications to self-gravitating superfluids are discussed. And a phase diagram for spinning and exploding Neutron stars is presented.
Abstract: Microscopic Theory of the Nuclear Equation of State and Neutron Star Structure.- Superfluidity in Neutron Star Matter.- Relativistic Superfluid Models for Rotating Neutron Stars.- The Tensor Virial Method and Its Applications to Self-Gravitating Superfluids.- Neutron Star Crusts.- Kaon Condensation in Neutron Stars.- Phases of QCD at High Baryon Density.- Diquarks in Dense Matter.- Color Superconductivity in Compact Stars.- Strange Quark Stars: Structural Properties and Possible Signatures for Their Existence.- Phase Diagram for Spinning and Accreting Neutron Stars.- Signal of Quark Deconfinement in Millisecond Pulsars and Reconfinement in Accreting X-ray Neutron Stars.- Supernova Explosions and Neutron Star Formation.- Evolution of a Neutron Star from Its Birth to Old Age.- Neutron Star Kicks and Asymmetric Supernovae.- Spin and Magnetism in Old Neutron Stars.- Neutrino Cooling of Neutron Stars: Medium Effects.
244 citations
TL;DR: In this article, cold quark matter in perturbation theory is considered and the results depend sensitively on the choice of the renormalization mass scale, and certain choices of this scale correspond to a strongly first order chiral transition, and generate quark stars with maximum masses and radii approximately half that of ordinary neutron stars.
Abstract: As a model for nonideal behavior in the equation of state of QCD at high density, we consider cold quark matter in perturbation theory. To second order in the strong coupling constant ${\ensuremath{\alpha}}_{s},$ the results depend sensitively on the choice of the renormalization mass scale. Certain choices of this scale correspond to a strongly first order chiral transition, and generate quark stars with maximum masses and radii approximately half that of ordinary neutron stars. At the center of these stars, quarks are essentially massless.
212 citations
TL;DR: In this article, a relativistically covariant quark model based on the Bethe-Salpeter equation with instantaneous two-and three-body forces was proposed to describe the hyperfine structure of the baryon spectrum.
Abstract: This is the third of a series of papers treating light baryon resonances up to 3 GeV within a relativistically covariant quark model based on the Bethe-Salpeter equation with instantaneous two- and three-body forces. In this last paper we extend our previous work on non-strange baryons to a prediction of the complete strange baryon spectrum and a detailed comparison with experiment. We apply our covariant Salpeter framework to specific quark models as introduced in the two preceding papers. Quark confinement is realized by linearly rising three-body string potentials with appropriate Dirac structures; to describe the hyperfine structure of the baryon spectrum we adopt 't Hooft's two-quark residual interaction based on QCD instanton effects. The investigation of instanton-induced effects in the baryon mass spectrum plays a central role in this work. We demonstrate that several prominent features of the excited strange mass spectrum, e.g. the low positions of the strange partners of the Roper resonance or the appearance of approximate ''parity doublets'' in the Lambda-spectrum, find a natural, uniform explanation in our relativistic quark model with instanton-induced forces.
169 citations
01 Jan 2001
TL;DR: In fact, during more than two decades of neutron-star physics the presence of neutron and proton superfluid phases has been invoked to explain the dynamical and thermal evolution of a neutron star as discussed by the authors.
Abstract: The research on the superfluidity of neutron matter can be traced back to Migdal’s observation that neutron stars are good candidates for being macroscopic superfluid systems [1] And, in fact, during more than two decades of neutron-star physics the presence of neutron and proton superfluid phases has been invoked to explain the dynamical and thermal evolution of a neutron star The most striking evidence is given by post-glitch timing observations [2],[3], but also the cooling history is strongly influenced by the possible presence of super- fluid phases [4],[5] On the theoretical side, the onset of superfluidity in neutron matter or in the more general context of nuclear matter was investigated soon after the formulation of the Bardeen, Cooper, and Schrieffer (BCS) theory of superconductivity [6] and the pairing theory in atomic nuclei [7],[8]
143 citations
TL;DR: In this paper, the authors explore the scenario where the core of a neutron star shrinks into the equilibrated quark object after reaching strange quark matter saturation density (where a composition of up, down and strange quarks is the favored state of matter), leading to a wide variety of ejectae ranging from the Newtonian, "dirty" to the ultrarelativistic fireball.
Abstract: We explore the scenario where the core of a neutron star (having experienced a transition to an up and down quark phase) shrinks into the equilibrated quark object after reaching strange quark matter saturation density (where a composition of up, down and strange quarks is the favored state of matter). The overlaying (envelope) material free-falls following the core contraction releasing upto 10^{53} {\rm ergs} in energy as radiation, partly as a result of the conversion of envelope material to quarks. This phenomena, we named Quark-Nova, leads to a wide variety of ejectae ranging form the Newtonian, "dirty" to the ultra-relativistic fireball. The mass range of the corresponding compact remnant (the quark star) ranges from less than 0.3M_{\odot} up to a solar mass. We discuss the connection between Quark-Novae and Gamma ray bursts and suggest the recently studied GRB011211 event as a plausible Quark-Nova candidate.
119 citations
TL;DR: In this paper, the thermal luminosity of a hot strange star in both photons and e+e-pair was estimated using the Coulomb barrier at the quark surface of the star.
Abstract: We consider the thermal emission of photons and e+e- pairs from the bare quark surface of a hot strange star. The radiation of high-energy (20 MeV) equilibrium photons prevails at the surface temperature TS 5 × 1010 K, while below this temperature, 8 × 108 K TS < 5 × 1010 K, emission of e+e- pairs created by the Coulomb barrier at the quark surface dominates. The thermal luminosity of a hot strange star in both photons and e+e- pairs is estimated.
91 citations
TL;DR: In this paper, the properties of charge-neutral cold quark matter within the Nambu-Jona-Lasinio model were investigated for different ratios of coupling constants characterizing the vector and scalar 4-fermion interaction.
Abstract: We investigate the properties of charge-neutral \ensuremath{\beta}-equilibrium cold quark matter within the Nambu--Jona-Lasinio model. The calculations are carried out for different ratios of coupling constants characterizing the vector and scalar 4-fermion interaction $\ensuremath{\xi}\ensuremath{\equiv}{G}_{V}{/G}_{S}.$ It is shown that for $\ensuremath{\xi}l0.4$ matter is self-bound and for $\ensuremath{\xi}l0.65$ it has a first order phase transition of the liquid-gas type. The Gibbs conditions in the mixed phase are applied for the case of two chemical potentials associated with the baryon number and electric charge. The characteristics of the quark stars are calculated for $\ensuremath{\xi}=0,$ 0.5, and 1. It is found that the phase transition leads to a strong density variation at the surface of these stars. For $\ensuremath{\xi}=1$ the properties of quark stars show behaviors typical for neutron stars. At $\ensuremath{\xi}\ensuremath{\gtrsim}0.4$ the stars near to the maximum mass have a large admixture of strange quarks in their interiors.
72 citations
TL;DR: In this article, the consequences of superconducting quark cores for evolution of temperature proles and the cooling curves in quark-hadron hybrid stars and in hypothetical self-bounded objects having no a hadron shell (quark core neutron stars).
Abstract: We study the consequences of superconduct- ing quark cores (with color-flavor-locked phase as repre- sentative example) for evolution of temperature proles and the cooling curves in quark-hadron hybrid stars and in hypothetical self-bounded objects having no a hadron shell (quark core neutron stars). The quark gaps are var- ied from 0t oq = 50 MeV. For hybrid stars we nd time scales of 1 5, 5 10 and 50 100 years for the formation of a quasistationary temperature distribution in the cases q = 0, 0.1 MeV and > 1 MeV, respectively. These time scales are governed by the heat transport within quark cores for large diquark gaps ( > 1 MeV) and within the hadron shell for small diquark gaps ( 10 MeV and a very short one for < 1 MeV. If hot young compact objects will be observed they can be interpreted as manifestation of large gap color superconductivity. Depending on the size of the pairing gaps, the compact star takes dierent paths in the lgTs vs. lgt diagram where Ts is the surface tem- perature. Compared to the corresponding hadronic model which well ts existing data the model for the hybrid neu- tron star (with a large diquark gap) shows too fast cooling. The same conclusion can be drawn for the corresponding self-bound objects.
64 citations
TL;DR: In this article, the possibility and implications of the idea that pulsars are born as strange stars are explored, and several possible criteria to distinguish BPCSSs from neutron stars are proposed.
58 citations
TL;DR: In this article, the authors compute the temperature profiles of accretion discs around rapidly rotating stars, using constant gravitational mass equilibrium sequences of these objects, considering the full effect of general relativity.
Abstract: We compute the temperature profiles of accretion discs around rapidly rotating strange stars, using constant gravitational mass equilibrium sequences of these objects, considering the full effect of general relativity. Beyond a certain critical value of stellar angular momentum (J), we observe the radius ( $r_{\rm orb}$) of the innermost stable circular orbit (ISCO) to increase with J (a property seen neither in rotating black holes nor in rotating neutron stars). The reason for this is traced to the crucial dependence of ${\rm d}r_{\rm orb}/{\rm d}J$ on the rate of change of the radial gradient of the Keplerian angular velocity at $r_{\rm orb}$ with respect to J. The structure parameters and temperature profiles obtained are compared with those of neutron stars, as an attempt to provide signatures for distinguishing between the two. We show that when the full gamut of strange star equation of state models, with varying degrees of stiffness are considered, there exists a substantial overlap in properties of both neutron stars and strange stars. However, applying accretion disc model constraints to rule out stiff strange star equation of state models, we notice that neutron stars and strange stars exclusively occupy certain parameter spaces. This result implies the possibility of distinguishing these objects from each other by sensitive observations through future X-ray detectors.
TL;DR: In this article, the radiative decays of D*, B*, and other excited heavy mesons are analyzed in a relativistic quark model for the light degrees of freedom and in the limit of heavy quark spin-flavor symmetry.
Abstract: The radiative decays of D*, B*, and other excited heavy mesons are analyzed in a relativistic quark model for the light degrees of freedom and in the limit of heavy quark spin-flavor symmetry. The analysis of strong decays carried out in the corresponding chiral quark model is used to calculate the strong decays and determine the branching ratios of the radiative D* decays. Consistency with the observed branching ratios requires the inclusion of the heavy quark component of the electromagnetic current and the introduction of an anomalous magnetic moment for the light quark. It is observed that not only D, but also B meson transitions within a heavy quark spin multiplet are affected by the presence of the heavy quark current.
TL;DR: In this paper, a brief review of the phenomena expected in cold dense quark matter, colour superconductivity and colour-flavour locking, and some implications of recent developments in their understanding for the physics of compact stars are sketched.
Abstract: After a brief review of the phenomena expected in cold dense quark matter, colour superconductivity and colour-flavour locking, we sketch some implications of recent developments in our understanding of cold dense quark matter for the physics of compact stars. We give a more detailed summary of our recent work on crystalline colour superconductivity and the consequent realization that (some) pulsar glitches may originate in quark matter.
TL;DR: In this article, the authors show that the light curves of the giant bursts may be easily explained in the model where the burst radiation is produced by the bare quark surface of a strange star heated, for example, by impact of a massive comet-like object.
Abstract: Two giant flares were observed on 5 March 1979 and 27 August 1998 from the soft gamma-ray repeaters SGR 0526-66 and SGR 1900+14, respectively. The striking similarity between these remarkable bursts strongly implies a common nature. We show that the light curves of the giant bursts may be easily explained in the model where the burst radiation is produced by the bare quark surface of a strange star heated, for example, by impact of a massive comet-like object.
TL;DR: In this paper, a quark-meson coupling model based on SU(L) x SU(3)(R) symmetry and scale invariance is proposed, and the effective baryon masses, binding energy and hyperon ratios are discussed with four types of confining potentials.
01 Jan 2001
TL;DR: In this article, the neutrino emission from the dense hadronic component in neutron stars is subject to strong modifications due to collective effects in nuclear matter with the most important in-medium processes incorporated in the cooling code an overall agreement with available soft X ray data can be easily achieved.
Abstract: This review demonstrates that the neutrino emission from the dense hadronic component in neutron stars is subject to strong modifications due to collective effects in nuclear matter With the most important in-medium processes incorporated in the cooling code an overall agreement with available soft X ray data can be easily achieved With these findings so called “standard” and “non-standard” cooling scenarios are replaced by one general “nuclear medium cooling scenario” which relates slow and rapid neutron star coolings to the star masses (interior densities) In-medium effects play an important role also in the early hot stage of the neutron star evolution by decreasing the neutrino opacity for less massive and increasing it for more massive neutron stars A formalism for the calculation of the neutrino radiation from nuclear matter is presented that treats on equal footing one-nucleon and multiple-nucleon processes as well as reactions with resonance bosons and condensates The cooling history of neutron stars with quark cores is also discussed
TL;DR: For the low energy Standard Model neutrino-matter interactions, in this article, the authors showed that the ratio of baryon to quark ν ν emissivities lies in the range 2 − 5 for the densities of interest in the long-term cooling of solar mass compact stars.
TL;DR: In this article, the authors suggest that a dipole magnetic field is relevant to the radio emission of the millisecond pulsar (PSR 1937+21) due to its low mass, small radius and weak magnetic moment.
Abstract: According to the observational limits on the radius and mass, the fastest rotating pulsar (PSR 1937+21) is probably a strange star, or at least some neutron star equations of state should be ruled out, if we suggest that a dipole magnetic field is relevant to its radio emission. We presume that the millisecond pulsar is a strange star with much low mass, small radius and weak magnetic moment.
TL;DR: In this paper, the decay modes of light baryon resonances are investigated within a chiral quark model whose hyperfine interaction is based on Goldstone-boson exchange.
Abstract: π and η decay modes of light baryon resonances are investigated within a chiral quark model whose hyperfine interaction is based on Goldstone-boson exchange. For the decay mechanism a modified version of the 3P0 model is employed. Our primary aim is to provide a further test of the recently proposed Goldstone-boson exchange constituent quark model. We compare the predictions for π and η decay widths with experiment and also with results from a traditional one-gluon exchange constituent quark model. The differences between nonrelativistic and semirelativistic versions of the constituent quark models are outlined. We also discuss the sensitivity of the results on the parameterization of the meson wave function entering the 3P0 model.
TL;DR: In this article, the authors show the possible existence of compact stars having a surface composed of a mixed phase of quarks and hadrons, satisfying the Witten-Bodmer hypothesis, and for gravitationally bound stars.
TL;DR: In this paper, the authors assume that the millisecond pulsar is a strange star with a low mass, small radius, and weak magnetic moment, and they suggest that a dipole magnetic field is relevant to its radio emission.
Abstract: According to the observational limits on the radius and mass, the fastest rotating pulsar (PSR 1937+21) is probably a strange star, or at least some neutron star equations of state should be ruled out, if we suggest that a dipole magnetic field is relevant to its radio emission. We presume that the millisecond pulsar is a strange star with {\em much} low mass, small radius, and weak magnetic moment.
TL;DR: In this paper, the authors employed an equation of state (EOS) of strange quark matter based on the MIT Bag Model with massive strange quarks and lowest order QCD interactions.
Abstract: Calculations of the properties of rotating strange stars with crusts are performed within the framework of general relativity. We employ an equation of state (EOS) of strange quark matter based on the MIT Bag Model with massive strange quarks and lowest order QCD interactions. The crust is described by the BPS equation of state. A signicant increase of the stellar radius is found close to the Keplerian (mass-shedding limit) conguration. This leads to the disappearance of the gap between the stellar surface and the innermost stable circular orbit (ISCO) at very high rotation rates, for a rather broad range of stellar masses. The Keplerian conguration for the strange star with crust corresponds to values of J, T=W, PISCO =1 =ISCO which are about 20% smaller than in the case of bare strange stars. Because the Keplerian conguration is achieved due to the increase of the stellar oblateness, the Keplerian frequency (of the rotation) remains almost unaltered. The lack of the gap close to the Keplerian rotation could imply a more stringent limit on ISCO, if the existence of such a gap is supported by observations, as in the source 4U 1820-30 with the upper QPO frequency 1.07 kHz. If such a constraint is taken into account (mandatory existence of a gap) the minimum ISCO is about 1 kHz even with the extreme ne tuning of strange quark matter parameters. The minimum ISCO is then obtained for the non-rotating conguration with maximum allowable mass. The maximum frequency in the stable circular orbit around the strange star with a crust is smaller by about 100 Hz than in the case of a bare strange star. During the spin-down of a magnetized strange quark star with crust, the crust matter is absorbed in the equatorial region by the strange matter core. The deconnement of absorbed crust matter is a strongly exothermic process, which would influence the cooling curve of this compact object.
TL;DR: In this paper, it was shown that for very rapidly rotating low-mass strange stars the marginally stable orbit is located above the stellar surface, which is explained by the very important role of the oblateness of the rotating strange star.
Abstract: It is shown that for very rapidly rotating low-mass strange stars the marginally stable orbit is located above the stellar surface. This effect is explained by the very important role of the oblateness of the rotating strange star. The comparison with some ``academic'' examples is presented. This feature is purely Newtonian in its nature and has nothing to do with relativistic marginally stable orbit. The effect is very large and cannot be treated in a perturbative way. It seems that strange stars as very dense self-bound objects are the only possibility in nature to represent these toy models.
TL;DR: In this paper, it was shown that large-scale convection also occurs with properties similar to those of convection in protoneutron stars (PNSs) and that the magnetic fields of PNSs may also behave very differently during the accretion phase when the fields decay.
Abstract: It is shown that protostrange stars (PSSs) can be convective and that there are two possible scenarios describing their turbulence. Besides the local turbulence on the scale which is less than the mean free path of neutrinos, large-scale (~1 km) convection also may occur with properties that are similar to those of convection in protoneutron stars (PNSs). We thus suggest that strange stars can also create dynamo-originated magnetic fields during the deleptonization episode soon after a supernova explosion. Further detailed investigations are needed to see whether or not strange stars and neutron stars can be distinguished according to the differences in dynamo actions in strange quark matter and in neutron matter. The magnetic fields of strange stars and neutron stars may also behave very differently during the accretion-phase when the fields decay.
TL;DR: In this paper, the authors studied the structural properties of a new class of stellar compact objects, called "strange quark stars", and showed that the total amount of energy liberated in the conversion process is in the range (1 - 4) x 1053 erg, in agreement with the energy required to power gamma-ray bursts at cosmological distances.
Abstract: We give a brief introduction to the physics of strange quark matter, and explore the possibility this novel deconfined phase of matter might be absolutely stable. Strange quark stars represent one of the most intriguing consequences of such a possibility. We study the structural properties of this hypothetical new class of stellar compact objects, both for non-rotating and rapidly rotating configurations in general relativity. Next, using recent observational data for the X-ray burster 4U 1820-30, the newly discovered millisecond X-ray pulsar SAX J1808.4-3658, and for the atoll source 4U 1728-34, we argue that the compact stars in these X-ray sources are likely strange star candidates. Finally, we study the conversion of a neutron star to a strange quark star. We show that the total amount of energy liberated in the conversion process is in the range (1 - 4) x 1053 erg, in agreement with the energy required to power gamma-ray bursts at cosmological distances.
TL;DR: In this article, the neutrino opacities in the evolution of a proto-neutron star containing quark matter have been studied, and it was shown that the appearance of quarks in baryonic matter drastically reduces neutrinos opacity for a given entropy.
Abstract: Neutrino opacities important in the evolution of a proto-neutron star containing quark matter are studied. The results for pure quark matter are compared with limiting expressions previously derived, and are generalized to the temperatures, neutrino degeneracies and lepton contents encountered in a proto-neutron star's evolution. We find that the appearance of quarks in baryonic matter drastically reduces the neutrino opacity for a given entropy, the reduction being sensitive to the thermodynamic conditions in the mixed quark-hadron phase.
TL;DR: In this paper, the authors studied the thermal emission of e+e- pairs from a bare strange star heated by energy input onto its surface; heating starts at some moment and is steady afterward.
Abstract: We study numerically the thermal emission of e+e- pairs from a bare strange star heated by energy input onto its surface; heating starts at some moment and is steady afterward. The thermal luminosity in e+e- pairs increases to some constant value. The rise time and the steady thermal luminosity are evaluated. Both normal and color superconducting states of the strange quark matter are considered. The results are used to test the model of soft gamma-ray repeaters in which the bursting activity is explained by the fast decay of superstrong magnetic fields and the heating of the strange star surface. It is shown that the rise times observed in typical bursts may be explained in this model only if the strange quark matter is a superconductor with an energy gap of more than 1 MeV.
TL;DR: In this paper, the authors studied the thermal emission of a bare star heated by energy input onto its surface; heating starts at some moment, and is steady afterwards The thermal luminosity in $e+e^-$ pairs increases to some constant value The rise time and the steady thermal emission are evaluated both normal and colour superconducting states of strange quark matter.
Abstract: We study numerically the thermal emission of $e^+e^-$ pairs from a bare strange star heated by energy input onto its surface; heating starts at some moment, and is steady afterwards The thermal luminosity in $e^+e^-$ pairs increases to some constant value The rise time and the steady thermal luminosity are evaluated Both normal and colour superconducting states of strange quark matter are considered The results are used to test the magnetar model of soft gamma-ray repeaters where the bursting activity is explained by fast decay of superstrong magnetic fields and heating of the strange star surface It is shown that the rise times observed in typical bursts may be explained in this model only if strange quark matter is a superconductor with an energy gap of more that 1 MeV
01 Mar 2001
TL;DR: In this article, a study of light hadron spectrum and quark masses in QCD with two flavors of dynamical quarks is presented, with the plaquette gauge action and the non-pertubatively O ( a ) improved Wilson quark action.
Abstract: We report on our study of light hadron spectrum and quark masses in QCD with two flavors of dynamical quarks. Simulations are made with the plaquette gauge action and the non-pertubatively O ( a ) improved Wilson quark action. We simulate 5 sea qaurk masses corresponding to m PS / m V ⋍ 0.8-0.6 at β = 5.2 on 12 3 × 48, 16 3 × 48 and 20 3 × 48 lattices. A comparison with previous calculations in quenched QCD indicates sea quark effects in meson and quark masses.
TL;DR: In this paper, the authors employed an equation of state (EOS) of strange quark matter based on the MIT Bag Model with massive strange quarks and lowest order QCD interactions.
Abstract: Calculations of the properties of rotating strange stars with crusts are performed within the framework of general relativity. We employ an equation of state (EOS) of strange quark matter based on the MIT Bag Model with massive strange quarks and lowest order QCD interactions. The crust is described by the BPS equation of state. A significant increase of the stellar radius is found close to the Keplerian (mass-shedding limit) configuration. This leads to the disappearance of the gap between the stellar surface and the innermost stable circular orbit (ISCO) at very high rotation rates, for a rather broad range of stellar masses. The Keplerian configuration for the strange star with crust corresponds to values of J, T/W which are about 20% smaller than in the case of bare strange stars. Because the Keplerian configuration is achieved due to the increase of the stellar oblateness, the Keplerian frequency (of the rotation) remains almost unaltered. The lack of the gap close to the Keplerian rotation could imply a more stringent limit on the frequency of the ISCO, if the existence of such a gap is supported by observations, as in the source 4U 1820-30 with the upper QPO frequency 1.07 kHz. During the spin-down of a magnetized strange quark star with crust, the crust matter is absorbed in the equatorial region by the strange matter core. The deconfinement of absorbed crust matter is a strongly exothermic process, which would influence the cooling curve of this compact object.