550 research outputs found
Kaon condensation in neutron stars and high density behaviour of nuclear symmetry energy
We study the influence of a high density behaviour of the nuclear symmetry
energy on a kaon condensation in neutron stars. We find that the symmetry
energy typical for several realistic nuclear potentials, which decreases at
high densities, inhibits kaon condensation for weaker kaon-nucleon couplings.
There exists a threshold coupling above which the kaon condensate forms at
densities exceeding some critical value. This is in contrast to the case of
rising symmetry energy, as e.g. for relativistic mean field models, when the
kaon condensate can form for any coupling at a sufficiently high density.
Properties of the condensate are also different in both cases.Comment: 12 pages, 7 figures, Acta Phys. Pol. B in pres
Kaon Condensates, Nuclear Symmetry Energy and Cooling of Neutron Stars
The cooling of neutron stars by URCA processes in the kaon-condensed neutron
star matter for various forms of nuclear symmetry energy is investigated. The
kaon-nucleon interactions are described by a chiral lagrangian. Nuclear matter
energy is parametrized in terms of the isoscalar contribution and the nuclear
symmetry energy in the isovector sector. High density behaviour of nuclear
symmetry energy plays an essential role in determining the composition of the
kaon-condensed neutron star matter which in turn affects the cooling
properties. We find that the symmetry energy which decreases at higher
densities makes the kaon-condensed neutron star matter fully protonized. This
effect inhibits strongly direct URCA processes resulting in slower cooling of
neutron stars as only kaon-induced URCA cycles are present. In contrast, for
increasing symmetry energy direct URCA processes are allowed in the almost
whole density range where the kaon condensation exists.Comment: 19 pages, 8 figures, elsart clas
Shell model study of the pairing correlations
A systematic study of the pairing correlations as a function of temperature
and angular momentum has been performed in the sd-shell region using the
spherical shell model approach. The pairing correlations have been derived for
even-even, even-odd and odd-odd systems near N=Z and also for the asymmetric
case of N=Z+4. The results indicate that the pairing content and the behavior
of pair correlations is similar in even-even and odd-mass nuclei. For odd-odd
N=Z system, angular momentum I=0 state is an isospin, t=1 neutron-proton paired
configuration. Further, these t=1 correlations are shown to be dramatically
reduced for the asymmetric case of N=Z+4. The shell model results obtained are
qualitatively explained within a simplified degenerate model
Low Energy Skyrmion-Skyrmion Scattering
We study the scattering of Skyrmions at low energy and large separation using
the method proposed by Manton of truncation to a finite number of degrees
freedom. We calculate the induced metric on the manifold of the union of
gradient flow curves, which for large separation, to first non-trivial order is
parametrized by the variables of the product ansatz. (presented at the Lake
Louise Winter Institute, 1994)Comment: 6 page
Is dark matter present in NGC4736? An iterative spectral method for finding mass distribution in spiral galaxies
An iterative method for reconstructing mass distribution in spiral galaxies
using a thin disk approximation is developed. As an example, the method is
applied to galaxy NGC 4736; its rotation curve does not allow one to employ a
model with a massive spherical halo. We find a global mass distribution in this
galaxy (without non-baryonic dark matter) that agrees perfectly with the high
resolution rotation curve of the galaxy. This mass distribution is consistent
with the -band luminosity profile with the mean mass-to-light ratio
, and also agrees with the amount of hydrogen observed in the
outermost regions of the galaxy. We predict the total mass of the galaxy to be
only 3.43\times10^{10}M_{\sun}. It is very close to the value predicted by
the modified gravity models and much less than the currently accepted value of
5.0\times10^{10}M_{\sun} (with of the mass in a dark matter
halo).Comment: in v2 version: 1) changed the reference luminosities of the Sun in
different bands - this affects mass-to-light ratio, giving more reliable 1.2
in the I-band, 2) found typos corrected, 3) corrected references to
literature, figures and equations 4) text permutations + language
corrections, accepted for publication in ApJ, May 200
Nuclear Matter in Relativistic Mean Field Theory with Isovector Scalar Meson
Relativistic mean field (RMF) theory of nuclear matter with the isovector
scalar mean field corresponding to the delta-meson [a_0(980)] is studied. While
the delta-meson mean field vanishes in symmetric nuclear matter, it can
influence properties of asymmetric nuclear matter in neutron stars. The RMF
contribution due to delta-field to the nuclear symmetry energy is negative. To
fit the empirical value, E_s=30 MeV, a stronger rho-meson coupling is required
than in the absence of the delta-field. The energy per particle of neutron
matter is then larger at high densities than the one with no delta-field
included. Also, the proton fraction of beta-stable matter increases. Splitting
of proton and neutron effective masses due to the delta-field can affect
transport properties of neutron star matter.Comment: 13 pages, plain TeX, 6 figures, Physics Letters B in pres
Equation of state for dense supernova matter
We provide an equation of state for high density supernova matter by applying
a momentum-dependent effective interaction. We focus on the study of the
equation of state of high-density and high-temperature nuclear matter
containing leptons (electrons and neutrinos) under the chemical equilibrium
condition. The conditions of charge neutrality and equilibrium under
-decay process lead first to the evaluation of the lepton fractions and
afterwards the evaluation of internal energy, pressure, entropy and in total to
the equation of state of hot nuclear matter for various isothermal cases.
Thermal effects on the properties and equation of state of nuclear matter are
evaluated and analyzed in the framework of the proposed effective interaction
model. Since supernova matter is characterized by a constant entropy we also
present the thermodynamic properties for isentropic case. Special attention is
dedicated to the study of the contribution of the components of -stable
nuclear matter to the entropy per particle, a quantity of great interest for
the study of structure and collapse of supernova.Comment: 23 pages, 15 figure
Skyrmions from a Born-Infeld Action
We consider a geometrically motivated Skyrme model based on a general
covariant kinetic term proposed originally by Born and Infeld. We introduce
this new term by generalizing the Born-Infeld action to a non-abelian
gauge theory and by using the hidden gauge symmetry formalism. The static
properties of the Skyrmion are then analyzed and compared with other
Skyrme-like models.Comment: 11 pages, 4 figures (not included), revtex v3, LAVAL-PHY-11-9
- …