33 research outputs found
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
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
Kaon production in heavy-ion collisions and maximum mass of neutron stars
We determine an `empirical' kaon dispersion relation by analysing and fitting
recent experimental data on kaon production in heavy-ion collisions. We then
investigate its effects on hadronic equation of state at high densities and on
neutron star properties. We find that the maximum mass of neutron stars can be
lowered by about 0.4, once kaon condensation as constrained by our
empirical dispersion relation is introduced. We emphasize the growing interplay
between hadron physics, relativistic heavy-ion physics and the physics of
compact objects in astrophysics.Comment: 6 pages with 3 postscript figures, to appear in Physical Review
Letter
Kaon effective mass and energy from a novel chiral SU(3)-symmetric Lagrangian
A new chiral SU(3) Lagrangian is proposed to describe the properties of kaons
and antikaons in the nuclear medium, the ground state of dense matter and the
kaon-nuclear interactions consistently.
The saturation properties of nuclear matter are reproduced as well as the
results of the Dirac-Br\"{u}ckner theory. Our numerical results show that the
kaon effective mass might be changed only moderately in the nuclear medium due
to the highly non-linear density effects. After taking into account the
coupling between the omega meson and the kaon, we obtain similar results for
the effective kaon and antikaon energies as calculated in the
one-boson-exchange model while in our model the parameters of the kaon-nuclear
interactions are constrained by the SU(3) chiral symmetry.Comment: 13 pages, Latex, 3 PostScript figures included; replaced by the
revised version, to appear in Phys. Rev.
Strange nuclear matter within Brueckner-Hartree-Fock Theory
We have developed a formalism for microscopic Brueckner-type calculations of
dense nuclear matter that includes all types of baryon-baryon interactions and
allows to treat any asymmetry on the fractions of the different species (n, p,
, , , , and ). We present
results for the different single-particle potentials focussing on situations
that can be relevant in future microscopic studies of beta-stable neutron star
matter with strangeness. We find the both the hyperon-nucleon and
hyperon-hyperon interactions play a non-negligible role in determining the
chemical potentials of the different species.Comment: 36 pages, LateX, includes 8 PostScript figures, (submitted to PRC
Application of the density dependent hadron field theory to neutron star matter
The density dependent hadron field (DDRH) theory, previously applied to
isospin nuclei and hypernuclei is used to describe -stable matter and
neutron stars under consideration of the complete baryon octet. The
meson-hyperon vertices are derived from Dirac-Brueckner calculations of nuclear
matter and extended to hyperons. We examine properties of density dependent
interactions derived from the Bonn A and from the Groningen NN potential as
well as phenomenological interactions. The consistent treatment of the density
dependence introduces rearrangement terms in the expression for the baryon
chemical potential. This leads to a more complex condition for the
-equilibrium compared to standard relativistic mean field (RMF)
approaches. We find a strong dependence of the equation of state and the
particle distribution on the choice of the vertex density dependence. Results
for neutron star masses and radii are presented. We find a good agreement with
other models for the maximum mass. Radii are smaller compared to RMF models and
indicate a closer agreement with results of non-relativistic Brueckner
calculations.Comment: 28 pages, 11 figure
S-wave Pairing of Hyperons in Dense Matter
In this work we calculate the gap energies of hyperons in
neutron star matter. The calculation is based on a solution of the BCS gap
equation for an effective G-matrix parameterization of the
interaction with a nuclear matter background, presented recently by Lanskoy and
Yamamoto. We find that a gap energy of a few tenths of MeV is expected for
Fermi momenta up to about 1.3 fm. Implications for neutron
star matter are examined, and suggest the existence of a
superfluid between the threshold baryon density for formation and the
baryon density where the fraction reaches .Comment: 16 pages, Revtex, 9 figures, 33 reference
In-medium Production of Kaons at the Mean-Field Level
The in-medium mass and energy of kaons and antikaons are studied within the
Relativistic Mean Field approach and compared with predictions from chiral
models by taking care of kaon-nucleon scattering data. Implications for the
subthreshold production of kaons and antikaons in heavy-ion collisions are
discussed. We find only small corrections due to in-medium effects on the
mean-field level for the relevant production processes for kaons. The
production of kaons is even less favourable at high density due to repulsive
vector interactions. We conclude that one has to go beyond mean-field
approaches and take fluctuations and secondary production processes into
account to explain the recently measured enhancement of kaon production at
subthreshold energies. The situation is different for antikaons where in-medium
effects strongly enhances their production rates. We also see strong in-medium
modifications of the annihilation processes of antikaons and Lambda's which
might be visible in flow measurements. At high density, we predict that the
threshold energy for antikaon and Lambda production and annihilation become
equal leading to similar numbers of antikaons and Lambda's in the dense zone of
a relativistic heavy ion collision.Comment: 32 pages, 5 Postscript figures, uses Revtex and epsf.st
Kaon Zero-Point Fluctuations in Neutron Star Matter
We investigate the contribution of zero-point motion, arising from
fluctuations in kaon modes, to the ground state properties of neutron star
matter containing a Bose condensate of kaons. The zero-point energy is derived
via the thermodynamic partition function, by integrating out fluctuations for
an arbitrary value of the condensate field. It is shown that the vacuum
counterterms of the chiral Lagrangian ensure the cancellation of divergences
dependent on , the charge chemical potential, which may be regarded as an
external vector potential. The total grand potential, consisting of the
tree-level potential, the zero-point contribution, and the counterterm
potential, is extremized to yield a locally charge neutral, beta-equilibrated
and minimum energy ground state. In some regions of parameter space we
encounter the well-known problem of a complex effective potential. Where the
potential is real and solutions can be obtained, the contributions from
fluctuations are found to be small in comparison with tree-level contributions.Comment: 40 pages RevTeX, 3 epsf figure
Nonequilibrium Weak Processes in Kaon Condensation II - Kinetics of condensation ---
The kinetics of negatively charged kaon condensation in the early stages of a
newly born neutron star is considered. The thermal kaon process, in which kaons
are thermally produced by nucleon-nucleon collisions, is found to be dominant
throughout the equilibration process. Temporal changes of the order parameter
of the condensate and the number densities of the chemical species are obtained
from the rate equations, which include the thermal kaon reactions as well as
the kaon-induced Urca and the modified Urca reactions. It is shown that the
dynamical evolution of the condensate is characterized by three stages: the
first, prior to establishment of a condensate, the second, during the growth
and subsequent saturation of the condensate, and the third, near chemical
equilibrium. The connection between the existence of a soft kaon mode and the
instability of the noncondensed state is discussed. Implications of the
nonequilibrium process on the possible delayed collapse of a protoneutron star
are also mentioned.Comment: 27 pages, incl. 8 eps figures, RevTe