266 research outputs found

### Surface Tension between Kaon Condensate and Normal Nuclear Matter Phase

We calculate for the first time the surface tension and curvature coefficient
of a first order phase transition between two possible phases of cold nuclear
matter, a normal nuclear matter phase in equilibrium with a kaon condensed
phase, at densities a few times the saturation density. We find the surface
tension is proportional to the difference in energy density between the two
phases squared. Furthermore, we show the consequences for the geometrical
structures of the mixed phase region in a neutron star.Comment: 7 pages, 5 figures (Latex

### Stability of the lattice formed in first-order phase transitions to matter containing strangeness in protoneutron stars

Well into the deleptonization phase of a core collapse supernova, a
first-order phase transition to matter with macroscopic strangeness content is
assumed to occur and lead to a structured lattice defined by negatively charged
strange droplets. The lattice is shown to crystallize for expected droplet
charges and separations at temperatures typically obtained during the
protoneutronstar evolution. The melting curve of the lattice for small
spherical droplets is presented. The one-component plasma model proves to be an
adequate description for the lattice in its solid phase with deformation modes
freezing out around the melting temperature. The mechanical stability against
shear stresses is such that velocities predicted for convective phenomena and
differential rotation during the Kelvin-Helmholtz cooling phase might prevent
the crystallization of the phase transition lattice. A solid lattice might be
fractured by transient convection, which could result in anisotropic neutrino
transport. The melting curve of the lattice is relevant for the mechanical
evolution of the protoneutronstar and therefore should be included in future
hydrodynamics simulations.Comment: accepted for publication in Physical Review

### The hadron-quark phase transition in dense matter and neutron stars

We study the hadron-quark phase transition in the interior of neutron stars
(NS's). We calculate the equation of state (EOS) of hadronic matter using the
Brueckner-Bethe-Goldstone formalism with realistic two-body and three-body
forces, as well as a relativistic mean field model. For quark matter we employ
the MIT bag model constraining the bag constant by using the indications coming
from the recent experimental results obtained at the CERN SPS on the formation
of a quark-gluon plasma. We find necessary to introduce a density dependent bag
parameter, and the corresponding consistent thermodynamical formalism. We
calculate the structure of NS interiors with the EOS comprising both phases,
and we find that the NS maximum masses fall in a relatively narrow interval,
$1.4 M_\odot \leq M_{\rm max} \leq 1.7 M_\odot$. The precise value of the
maximum mass turns out to be only weakly correlated with the value of the
energy density at the assumed transition point in nearly symmetric nuclear
matter.Comment: 25 pages, Revtex4, 16 figures included as postscrip

### The Lemaitre-Schwarzschild Problem Revisited

The Lemaitre and Schwarzschild analytical solutions for a relativistic
spherical body of constant density are linked together through the use of the
Weyl quadratic invariant. The critical radius for gravitational collapse of an
incompressible fluid is shown to vary continuously from 9/8 of the
Schwarzschild radius to the Schwarzschild radius itself while the internal
pressures become locally anisotropic.Comment: Final version as accepted by GR&G (to appear in vol. 34, september
2002

### Equation of state of neutron star cores and spin down of isolated pulsars

We study possible impact of a softening of the equation of state by a phase
transition, or appearance of hyperons, on the spin evolution of of isolated
pulsars. Numerical simulations are performed using exact 2-D simulations in
general relativity. The equation of state of dense matter at supranuclear
densities is poorly known. Therefore, the accent is put on the general
correlations between evolution and equation of state, and mathematical
strictness. General conjectures referring to the structure of the one-parameter
families of stationary configurations are formulated. The interplay of the back
bending phenomenon and stability with respect to axisymmetric perturbations is
described. Changes of pulsar parameters in a corequake following instability
are discussed, for a broad choice of phase transitions predicted by different
theories of dense matter. The energy release in a corequake, at a given initial
pressure, is shown to be independent of the angular momentum of collapsing
configuration. This result holds for various types of phases transition, with
and without metastability. We critically review observations of pulsars that
could be relevant for the detection of the signatures of the phase transition
in neutron star cores.Comment: 7 pages, 11 figures, to appear in Astrophysics and Space Science, in
the proceedings of "Isolated Neutron Stars: from the Interior to the
Surface", edited by D. Page, R. Turolla and S. Zan

### Negative Kaons in Dense Baryonic Matter

Kaon polarization operator in dense baryonic matter of arbitrary isotopic
composition is calculated including s- and p-wave kaon-baryon interactions. The
regular part of the polarization operator is extracted from the realistic
kaon-nucleon interaction based on the chiral and 1/N_c expansion. Contributions
of the Lambda(1116), Sigma(1195), Sigma*(1385) resonances are taken explicitly
into account in the pole and regular terms with inclusion of mean-field
potentials. The baryon-baryon correlations are incorporated and fluctuation
contributions are estimated. Results are applied for K- in neutron star matter.
Within our model a second-order phase transition to the s-wave K- condensate
state occurs at rho_c \gsim 4 \rho_0 once the baryon-baryon correlations are
included. We show that the second-order phase transition to the p-wave $K^-$
condensate state may occur at densities $\rho_c \sim 3\div 5 \rho_0$ in
dependence on the parameter choice. We demonstrate that a first-order phase
transition to a proton-enriched (approximately isospin-symmetric) nucleon
matter with a p-wave K- condensate can occur at smaller densities, \rho\lsim 2
\rho_0. The transition is accompanied by the suppression of hyperon
concentrations.Comment: 41 pages, 24 figures, revtex4 styl

### On the role of pressure anisotropy for relativistic stars admitting conformal motion

We investigate the spacetime of anisotropic stars admitting conformal motion.
The Einstein field equations are solved using different ansatz of the surface
tension. In this investigation, we study two cases in details with the
anisotropy as: [1] $p_t = n p_r$ [2] $p_t - p_r = \frac{1}{8
\pi}(\frac{c_1}{r^2} + c_2)$ where, n, $c_1$ and $c_2$ are arbitrary constants.
The solutions yield expressions of the physical quantities like pressure
gradients and the mass.Comment: 21 pages, accepted for publication in 'Astrophysics and Space
Science

### Warm stellar matter with deconfinement: application to compact stars

We investigate the properties of mixed stars formed by hadronic and quark
matter in $\beta$-equilibrium described by appropriate equations of state (EOS)
in the framework of relativistic mean-field theory. We use the non- linear
Walecka model for the hadron matter and the MIT Bag and the Nambu-Jona-Lasinio
models for the quark matter. The phase transition to a deconfined quark phase
is investigated. In particular, we study the dependence of the onset of a mixed
phase and a pure quark phase on the hyperon couplings, quark model and
properties of the hadronic model. We calculate the strangeness fraction with
baryonic density for the different EOS. With the NJL model the strangeness
content in the mixed phase decreases. The calculations were performed for T=0
and for finite temperatures in order to describe neutron and proto-neutron
stars. The star properties are discussed. Both the Bag model and the NJL model
predict a mixed phase in the interior of the star. Maximum allowed masses for
proto-neutron stars are larger for the NJL model ($\sim 1.9$ M$_{\bigodot}$)
than for the Bag model ($\sim 1.6$ M$_{\bigodot}$).Comment: RevTeX,14 figures, accepted to publication in Physical Review

### Quark Hadron Phase Transition and Hybrid Stars

We investigate the properties of hybrid stars consisting of quark matter in
the core and hadron matter in outer region. The hadronic and quark matter
equations of state are calculated by using nonlinear Walecka model and chiral
colour dielectric (CCD) model respectively. We find that the phase transition
from hadron to quark matter is possible in a narrow range of the parameters of
nonlinear Walecka and CCD models. The transition is strong or weak first order
depending on the parameters used. The EOS thus obtained, is used to study the
properties of hybrid stars. We find that the calculated hybrid star properties
are similar to those of pure neutron stars.Comment: 25 pages in LaTex and 9 figures available on request, IP/BBSR/94-3

### Density dependent hadron field theory for neutron stars with antikaon condensates

We investigate $K^-$ and $\bar K^0$ condensation in $\beta$-equilibrated
hyperonic matter within a density dependent hadron field theoretical model. In
this model, baryon-baryon and (anti)kaon-baryon interactions are mediated by
the exchange of mesons. Density dependent meson-baryon coupling constants are
obtained from microscopic Dirac Brueckner calculations using Groningen and Bonn
A nucleon-nucleon potential. It is found that the threshold of antikaon
condensation is not only sensitive to the equation of state but also to
antikaon optical potential depth. Only for large values of antikaon optical
potential depth, $K^-$ condensation sets in even in the presence of negatively
charged hyperons. The threshold of $\bar K^0$ condensation is always reached
after $K^-$ condensation. Antikaon condensation makes the equation of state
softer thus resulting in smaller maximum mass stars compared with the case
without any condensate.Comment: 20 pages, 7 figures; final version to appear in Physical Review

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