860 research outputs found
Strangeness in Compact Stars and Signal of Deconfinement
Phase transitions in compact stars are discussed including hyperonization,
deconfinement and crystalline phases. Reasons why kaon condensation is unlikely
is reviewed. Particular emphasis is placed on the evolution of internal
structure with spin-down of pulsars. A signature of a first order phase
transition in the timing structure of pulsars which is strong and easy to
measure, is identified.Comment: 17 pages, 15 figures, Latex. (Invited Talk at the International
Symposium on ``Strangeness In Quark Matter 1997'', Thera (Santorini), Hellas,
April 14-18, 1997, To be published in Journal of Physics G (Organizers: A
Panagiotou and J. Madsen
Mapping Deconfinement with a Compact Star Phase Diagram
We have found correlations between properties of the equation of state for
stellar matter with a phase transition at supernuclear densities and two
characteristic features of a "phase diagram" for rotating compact stars in the
angular velocity - baryon number plane: 1) the critical dividing line between
mono- and two-phase star configurations and 2) the maximum mass line. The
second line corresponds to the minimum mass function for black hole candidates
whereas the first one is observable by a population statistics, e.g. for
Z-sources in low-mass X-ray binaries. The observation of a population gap in
the mass distribution for the latter is suggested as an astrophysical
verification of the existence of a first order phase transition in QCD at high
densities such as the deconfinement.Comment: 4 pages, 2 figures, Contribution to Proceedings of Quark Matter 2002,
Nantes, July 18 - 24, 200
Probing dense matter in neutron stars with axial w-modes
We study the problem of extracting information about composition and equation
of state of dense matter in neutron star interior using axial w-modes. We
determine complex frequencies of axial w-modes for a set of equations of state
involving hyperons as well as Bose-Einstein condensates of antikaons adopting
the continued fraction method. Hyperons and antikaon condensates result in
softer equations of state leading to higher frequencies of first axial w-modes
than that of nuclear matter case, whereas the opposite happens in case of
damping times. The presence of condensates may lead to the appearance of a new
stable branch of superdense stars beyond the neutron star branch called the
third family. The existence of same mass compact stars in both branches are
known as neutron star twins. Further investigation of twins reveal that first
axial w-mode frequencies of superdense stars in the third family are higher
than those of the corresponding twins in the neutron star branch.Comment: LaTeX; 23 pages including two tables and 11 figure
Signal of Quark Deconfinement in the Timing Structure of Pulsar Spin-Down
The conversion of nuclear matter to quark matter in the core of a rotating
neutron star alters its moment of inertia. Hence the epoch over which
conversion takes place will be signaled in the spin-down "signal_prl.tex" 581
lines, 22203 characters characteristics of pulsars. We find that an observable
called the braking index should be easily measurable during the transition
epoch and can have a value far removed (by orders of magnitude) from the
canonical value of three expected for magnetic dipole radiation, and may have
either sign. The duration of the transition epoch is governed by the slow loss
of angular momentum to radiation and is further prolonged by the reduction in
the moment of inertia caused by the phase change which can even introduce an
era of spin-up. We estimate that about one in a hundred pulsars may be passing
through this phase. The phenomenon is analogous to ``bachbending'' observed in
the moment of inertia of rotating nuclei observed in the 1970's, which also
signaled a change in internal structure with changing spin.Comment: 5 pages, 4 figures, Revtex. (May 12, 1997, submitted to PRL
First Order Kaon Condensate
First order Bose condensation in asymmetric nuclear matter and in neutron
stars is studied, with particular reference to kaon condensation. We
demonstrate explicitly why the Maxwell construction fails to assure equilibrium
in multicomponent substances. Gibbs conditions and conservation laws require
that for phase equilibrium, the charge density must have opposite sign in the
two phases of isospin asymmetric nuclear matter. The mixed phase will therefore
form a Coulomb lattice with the rare phase occupying lattice sites in the
dominant phase. Moreover, the kaon condensed phase differs from the normal
phase, not by the mere presence of kaons in the first, but also by a difference
in the nucleon effective masses. The mixed phase region, which occupies a large
radial extent amounting to some kilometers in our model neutron stars, is thus
highly heterogeneous. It should be particularly interesting in connection with
the pulsar glitch phenomenon as well as transport properties.Comment: 25 pagees, 20 figures, Late
First Order Kaon Condensation in Neutron Stars: Finite Size Effects in the Mixed Phase
We study the role of Coulomb and surface effects on the phase transition from
dense nuclear matter to a mixed phase of nuclear and kaon-condensed matter. We
calculate corrections to the bulk calculation of the equation of state (EOS)
and the critical density for the transition by solving explicitly for
spherical, cylindrical, and planar structures. The importance of Debye
screening in the determination of the charged particle profiles is studied in
some detail. We find that the surface and Coulomb contributions to the energy
density are small, but that they play an important role in the determination of
the critical pressure for the transition, as well as affecting the size and
geometry of favored structures. This changes the EOS over a wide range of
pressure and consequently increases the maximum mass by about 0.1 solar masses.
Implications for transport properties of the mixed phase are also discussed.Comment: 18 pages, 6 figure
Kaon condensation in the quark-meson coupling model and compact stars
The properties of neutron stars constituted of a crust of hadrons and an
internal part of hadrons and kaon condensate are calculated within the
quark-meson-coupling model. We have considered stars with nucleons only in the
hadron phase and also stars with hyperons as well. The results are compared
with the ones obtained from the non-linear Walecka model for the hadronic
phase.Comment: 10 pages, 6 figure
Kaon Condensation and Dynamical Nucleons in Neutron Stars
We discuss the nature of the kaon condensation phase transition. We find
several features which, if kaons condense in neutron stars, are not only
remarkable, but must surely effect such properties as superfluidity and
transport properties, which in turn are relevant to the glitch phenomenon and
cooling rates of neutron stars. The mixed phase, because of the extensive
pressure range that it spans, will occupy a broad radial extent in a neutron
star. This region is permeated with microscopic drops (and other
configurations) located at lattice sites of one phase immersed in the
background of the other phase. The electric charge on drops is opposite to that
of the background phase {\sl and} nucleons have a mass approximately a factor
two different depending on whether they are in the drops or the background
phase. A large part of the stellar interior has this highly non-homogeneous
structure.Comment: 5 pages, 6 figures, revtex. Physical Review Letters (accepted
Nuclear incompressibility using the density dependent M3Y effective interaction
A density dependent M3Y effective nucleon-nucleon (NN) interaction which was
based on the G-matrix elements of the Reid-Elliott NN potential has been used
to determine the incompressibity of infinite nuclear matter. The nuclear
interaction potential obtained by folding in the density distribution functions
of two interacting nuclei with this density dependent M3Y effective interaction
had been shown earlier to provide excellent descriptions for medium and high
energy and heavy ion elastic scatterings as well as and heavy
cluster radioactivities. The density dependent parameters have been chosen to
reproduce the saturation energy per nucleon and the saturation density of spin
and isospin symmetric cold infinite nuclear matter. The result of such
calculations for nuclear incompressibility using the density dependent M3Y
effective interaction based on the G-matrix elements of Reid-Elliott NN
potential predicts a value of about 300 MeV for nuclear incompressibility.Comment: 4 Page
Relativistic Mean Field Calculations of and Hypernuclei
Single--particle spectra of and hypernuclei are
calculated within a relativistic mean--field theory. The hyperon couplings used
are compatible with the binding in saturated nuclear matter,
neutron-star masses and experimental data on levels in hypernuclei.
Special attention is devoted to the spin-orbit potential for the hyperons and
the influence of the -meson field (isospin dependent interaction).Comment: 18 pages, including 2 figs., figs. 1 and 4-6 available as
postscript-datasets on request; written in Latex, report# LBL-3303
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