Showing papers on "Quark star published in 1998"

Rotating Stars in Relativity

Abstract: Rotating relativistic stars have been studied extensively in recent years, both theoretically and observationally, because of the information they might yield about the equation of state of matter at extremely high densities and because they are considered to be promising sources of gravitational waves. The latest theoretical understanding of rotating stars in relativity is reviewed in this updated article. The sections on equilibrium properties and on nonaxisymmetric oscillations and instabilities in f-modes and r-modes have been updated. Several new sections have been added on equilibria in modified theories of gravity, approximate universal relationships, the one-arm spiral instability, on analytic solutions for the exterior spacetime, rotating stars in LMXBs, rotating strange stars, and on rotating stars in numerical relativity including both hydrodynamic and magnetohydrodynamic studies of these objects.

Physics and astrophysics of strange quark matter

Abstract: 3-flavor quark matter (strange quark matter; SQM) can be stable or metastable for a wide range of strong interaction parameters If so, SQM can play an important role in cosmology, neutron stars, cosmic ray physics, and relativistic heavy-ion collisions As an example of the intimate connections between astrophysics and heavy-ion collision physics, this Chapter gives an overview of the physical properties of SQM in bulk and of small-baryon number strangelets; discusses the possible formation, destruction, and implications of lumps of SQM (quark nuggets) in the early Universe; and describes the structure and signature of strange stars, as well as the formation and detection of strangelets in cosmic rays It is concluded, that astrophysical and laboratory searches are complementary in many respects, and that both should be pursued to test the intriguing possibility of a strange ground state for hadronic matter, and (more generally) to improve our knowledge of the strong interactions

Mass spectrum of orbitally and radially excited heavy-light mesons in the relativistic quark model

Abstract: The mass spectrum of orbitally and radially excited states of $B$ and $D$ mesons is calculated in the framework of the relativistic quark model. The expansion in inverse powers of the heavy quark mass is carried out up to first order, while the light quark is treated without expansion. We find that the relativistic treatment of the light quark plays an important role. Different patterns of $P$ level inversion are discussed. The obtained masses of orbitally and radially excited states are in accord with available experimental data and heavy quark symmetry relations.

Strange stars and related astrophysical phenomena

Abstract: Some historical remarks concerning the strange stars are briefly discussed The recent developments in physics and dynamical behavior of strange stars are reviewed Especially, various observational effects in distinguishing strange stars from neutron stars and related interesting astrophysical phenomena are also discussed

How to identify a strange star

Abstract: Contrary to young neutron stars, young strange stars are not subject to the r-mode instability which slows rapidly rotating, hot neutron stars to rotation periods near 10 ms via gravitational wave emission. Young millisecond pulsars are therefore likely to be strange stars rather than neutron stars, or at least to contain significant quantities of quark matter in the interior.

Effects of hyperons on the dynamical deconfinement transition in cold neutron star matter

Abstract: The influence of the presence of hyperons in dense hadronic matter on the quantum nucleation of quark matter is examined at low temperatures relevant to neutron star cores. We calculate the equation of state and the composition of matter before and after deconfinement by using a relativistic mean-field theory and an MIT bag model, respectively; the case in which hyperons are present in the hadronic system is considered, together with the case of the system without hyperons. We find that strangeness contained in hyperons acts to reduce a density jump at deconfinement as well as a lepton fraction in the hadronic phase. As a result of these reductions, a quark matter droplet being in a virtual or real state has its effective mass lightened and its electric charge diminished into nearly zero. The Coulomb screening of leptons on the droplet charge, which has significance to the droplet growth after nucleation in the absence of hyperons, is thus shown to be of little consequence. If the effective droplet mass is small enough to become comparable to the height of the potential barrier, the effect of relativity brings about an exponential increase in the rate of droplet formation via quantum tunneling, whereas the role played by energy dissipation in decelerating the droplet formation, dominant for matter without hyperons, becomes of less importance. For matter with and without hyperons, we estimate the overpressure needed to form the first droplet in the star during the compression due to stellar spin-down or mass accretion from a companion star. The temperature at which a crossover from the quantum nucleation to the Arrhenius-type thermal nucleation takes place is shown to be large compared with the temperature of matter in the core.

Is GRO J1744-28 a Strange Star?

Abstract: The unusual hard x-ray burster GRO J1744-28 recently discovered by the Compton Gamma-Ray Observatory can be modeled as a strange star with a dipolar magnetic field of ≤10 11 gauss. According to this model, when the accreted mass of the star exceeds some critical mass, its crust breaks, resulting in the conversion of the accreted matter into strange matter and a release of energy. Subsequently, a fireball forms and expands relativistically outward. The expanding fireball interacts with the surrounding interstellar medium, causing its kinetic energy to be radiated in shock waves and producing a burst of x-ray radiation. The burst energy, duration, interval, and spectrum derived from such a model are consistent with the observations of GRO J1744-28.

Non-Abelian Dipole Radiation and the Heavy Quark Expansion

Abstract: Dipole radiation in QCD is derived to the second order in $\alpha_s$. A power-like evolution of the spin-singlet heavy quark operators is obtained to the same accuracy. In particular, ${\cal O}(\alpha_s^2)$ relation between a short-distance low-scale running heavy quark mass and the $\barMS$ mass is given. We discuss the properties of the effective QCD coupling $\aw(E)$ which governs the dipole radiation. This coupling is advantageous for heavy quark physics.

Are Soft γ-Ray Repeaters Strange Stars?

Abstract: The soft $\ensuremath{\gamma}$-ray repeaters (SGRs) are proposed to result from young, magnetized strange stars with superconducting cores. As such a strange star spins down, the quantized vortex lines move outward and drag the magnetic flux tubes because of the strong coupling between them. Since the terminations of the tubes interact with the stellar crust, the dragged tubes can produce sufficient tension to crack the crust and pull parts of the broken platelet into the quark core. The deconfinement of crustal matter into strange quark matter will release energy. The model burst energy, duration, time interval, spectrum, and the persistent x-ray emission from SGRs are shown to be in agreement with observed results.

Effect of trapped neutrinos in the hadron matter to quark matter transition

Abstract: We study the transition from hadron matter to quark matter in the presence of a gas of trapped electron and muon neutrinos. We show that trapped neutrinos make the densities of hadron matter deconfinement noticeably higher than in the case in which neutrinos are not present. We discuss the possible consequences of this effect in supernova explosions and protoneutron star evolution.

Virtual Meson Cloud of the Nucleon and Intrinsic Strangeness and Charm

Abstract: We have used the Meson Cloud Model (MCM) to calculate the charm and strange antiquark distribution in the nucleon. The resulting curve, in the case of charm, is very similar to the intrinsic charm momentum distribution. This allows us to identify the intrinsic quark distribution with the valence quark distribution in the cloud and, at the same time, explains why other MCM calculations fail in reproducing the low x region data. From the intrinsic strange quark distribution in the nucleon, we have extracted information about the relative importance of various intermediate states that should be considered in a loop calculation.

The properties of strange stars in the quark mass– density–dependent model

Abstract: We study the general properties of compact objects made up of strange matter in the framework of a new equation of state in which the quark masses are parametrized as functions of the baryon density, so that they are heavy (light) at low (high) densities. This has been called the "quark mass-density-dependent model." In this approximation, the strange matter equation of state is rather similar to the corresponding to the MIT Bag Model, but it is significantly stiffer at low densities. Such a property modifies the structure of strange stars in a sizeable way. In this framework, we calculate the structure of strange stars (mass, radius, central density, gravitational redshift, moment of inertia, and total baryon number) finding that the resulting structures are rather similar to those obtained in the MIT Bag model, although some important differences appear. Comparing to the standard bagged case (with a bag constant in the range of B = 60 - 80 MeV fm-3), we find that these objects may be more massive and may show gravitational redshifts larger (up to ≈ 10%) than in the bag case. The moment of inertia and total baryon number may be larger than in the bagged case up to a factor of three. We also calculate the first three radial pulsation modes of these objects, finding that the relation of period vs. gravitational redshift is rather similar to the bag case. Also, we present an analytical treatment for such modes in the low-mass strange stars regime, which is in reasonable agreement with the numerical results.

Rotating compact objects with magnetic fields

Abstract: We consider here the structure of rotating compact objects endowed with a magnetic field in general relativity as models of pulsars. We discuss the structure of rotating stars in the framework of Hartle, taking different realistic equations of state, and study their effects on bulk properties of stars. We consider the possibility of rotating stars with a quark matter core. We also analyse the structure of the magnetic field in the interior of the star, as affected by different equations of state, as well as due to rotation.

Physics of Strange Matter

Abstract: Relativistic heavy ion collisions offer the possibility to produce exotic metastable states of nuclear matter containing (roughly) equal number of strangeness compared to the content in baryon number. The reasoning of both their stability and existence, the possible distillation of strangeness necessary for their formation and the chances for their detection are reviewed. In the later respect emphasize is put on the properties of small lumps of strange quark matter with respect to their stability against strong or weak hadronic decays. In addition, implications in astrophysics like the properties of neutron stars and the issue of baryonic dark matter will be discussed.

The Particle Century

Abstract: FROM THE ASHES The post-World War II period Decommissioning the Manhattan project Big science The establishment of major laboratories and new research infrastructure in the US, the USSR, and Europe COSMIC RAIN The discovery of new particles in cosmic rays Historical introduction and post-World War II achievements (pion, muon, strange particles) Recent developments FIRST ACCELERATOR FRUITS Particle beams and early detectors The discoveries of particle resonances in the 1950s and early 1960s, leading up to the discovery of the omega-minus in 1963 The bubble chamber THE 3-QUARK PICTURE The need for an underlying picture SU3 and mathematical techniques The quark model PROTON STRUCTURE The 1967 SLAC experiment Partons, scaling, and quarks GAUGE THEORY Field theory Yang-Mills schemes Different scenarios Spontaneous symmetry breaking and the Higgs mechanism Calculations and renormalizability Asymptotic freedom UNEXPECTED WINDFALL Electron-positron collider physics New particles in the early 1970s The fourth quark and tau-lepton WEAK INTERACTIONS Parity violation The role of the neutrino Its discovery Neutrino types Universality The (V-A) structure of the weak interaction The discovery of neutral currents Neutrinos as a physics tool THE WEAK FORCE CARRIERS Initial searches for the W The implications of the neutral current discovery Proton-antiproton collisions The lead-up to and discovery of the W and Z particles QUARK MATRIX Quark transitions The Cabibbo and Kobayashi-Maskawa schemes CP-violation The emergence of B physics Future goals QUARK GLUE Quark dynamics Gluon phenomena Quantum chromodynamics effects THE STANDARD MODEL Six quarks and six leptons Precision measurements Implications for the top quark Searching for the Higgs THE TOP QUARK Hunting and disentangling the top quark BEYOND THE STANDARD MODEL Unifying electroweak and quark forces Supersymmetry Grand unification THE TOOLS 1: ACCELERATORS Historical introduction Post-World War II scene Personalities Electron and proton machines Colliding beams versus fixed targets Superconductivity Major machines of the world The demise of the SSC The future THE TOOLS 2: DETECTORS Looking at particles Historical introduction The rise and fall of optical techniques Electronic detectors Colliders and the requirement for full solid-angle coverage The "typical" detector Triggering Data handling Spinoff applications ASTROPARTICLE PHYSICS The synthesis of micro- and macrophysics Big Bang overview BIG BANG DYNAMICS Inflation, microwave background radiation, galaxy formation ASTRONOMY The interplay of ground-based and space-borne platforms COBE, Hubble New telescopes OUTLOOK

Quark and Gluon Condensates in the Quark-Meson Coupling Model

Abstract: Using the quark–meson coupling (QMC) model, we study the density dependence of the quark and gluon condensates in nuclear matter. We show that the change of the quark condensate is mainly driven by the scalar field in the medium and that the reduction of the quark condensate is suppressed at high density, even in the mean-field approximation. The gluon condensate decreases by 4–6% at nuclear saturation density. We also give a simple relationship between the change of the quark condensate and that of a hadron mass in the medium.

Reply to comment on `Bare quark matter surfaces of strange stars and e+ e- emission'

Abstract: I reply to A. Mitra's comment on my PRL paper "Bare quark matter surfaces of strange stars and $e^+e^-$ emission". I show that his points of criticism are not correct.

Chemical Evolution of Strongly Magnetized Quark Core in a Newborn Neutron Star

Abstract: The chemical evolution of nascent quark matter core in a newborn compact neutron star is studied in presence of a strong magnetic field. The effective rate of strange quark production in degenerate quark matter core in presence of strong magnetic fields is obtained. The investigations show that in presence of strong magnetic fields a quark matter core becomes energetically unstable and hence a deconfinement transition to quark matter at the centre of a compact neutron star under such circumstances is not possible. The critical strength of magnetic field at the central core to make the system energetically unstable with respect to dense nuclear matter is found to be $\sim 4.4\times 10^{13}$G. This is the typical strength at which the Landau levels for electrons are populated. The other possible phase transitions at such high density and ultra strong magnetic field environment are discussed.

A red giant with a strange star as its core. Principal similarities to and differences from Thorne-Zytkow objects

Abstract: A model red giant with a mass of 5 M⊙ a luminosity of 41,740 L⊙, and a radius of 960 R⊙ and with a strange quark star as its core is constructed, and it is compared with a Thorne-Zytkow object having similar integrated parameters. The difference in internal structure is manifested right at the dense core: matter above the core is held off only by γ rays from the strange star, and convection is maintained down to the strange star. The lifetime of a red giant containing a strange star turns out to be almost 500 times shorter than that of a Thorne-Zytkow object — on the order of 105 years.

Can we see the hadron-quark transition happening in neutron stars?

Abstract: In order to actually see the hadron-quark transition happening in a neutron star, we point out and study two static conditions (the transition hadronic density must be lower than the neutron star maximum hadronic density; the neutron star mass at the transition hadronic density must be in the observed range ≈ 1.4 M☉) and one dynamical condition (nucleation must occur during the star lifetime). We find that the minicollapse accompanying the transition from metastable hadronic matter to quark matter may be relevant to explain macro-glitches and gamma-ray bursts, but that the mechanism increasing the star density must be relatively fast, e.g., accretion, but not slowing down. This rules out a scenario for gamma-ray bursts proposed recently.

The proton spin and flavor structure in the chiral quark model

Abstract: After a pedagogical review of the simple constituent quark model and deep inelastic sum rules, we describe how a quark sea as produced by the emission of internal Goldstone bosons by the valence quarks can account for the observed features of proton spin and flavor structures Some issues concerning the strange quark content of the nucleon are also discussed