80 research outputs found
Phase Transitions in Neutron Stars and Maximum Masses
Using the most recent realistic effective interactions for nuclear matter
with a smooth extrapolation to high densities including causality, we constrain
the equation of state and calculate maximum masses of rotating neutron stars.
First and second order phase transitions to, e.g., quark matter at high
densities are included. If neutron star masses of from
quasi-periodic oscillations in low mass X-ray binaries are confirmed, a soft
equation of state as well as strong phase transitions can be excluded in
neutron star cores.Comment: Replaced with revised version, 7 pages, 3 figs. To appear in Ap. J.
Let
Hyperon effects on the properties of -stable neutron star matter
We present results from Brueckner-Hartree-Fock calculations for
-stable neutron star matter with nucleonic and hyperonic degrees of
freedom employing the most recent parametrizations of the baryon-baryon
interaction of the Nijmegen group. Only and are present up
to densities . The corresponding equations of state are then used
to compute properties of neutron stars such as masses and radii.Comment: 4 pages, contributed talk at HYP2000, Torino, 23-27 Oct. 200
3P_2-3F_2 pairing in neutron matter with modern nucleon-nucleon potentials
We present results for the pairing gap in neutron matter with
several realistic nucleon-nucleon potentials, in particular with recent,
phase-shift equivalent potentials. We find that their predictions for the gap
cannot be trusted at densities above , where is
the saturation density for symmetric nuclear matter. In order to make
predictions above that density, potential models which fit the nucleon-nucleon
phase shifts up to about 1 GeV are required.Comment: Revtex style, 19 pages, 6 figures inlude
Modern nucleon-nucleon potentials and symmetry energy in infinite matter
We study the symmetry energy in infinite nuclear matter employing a
non-relativistic Brueckner-Hartree-Fock approach and using various new
nucleon-nucleon (NN) potentials, which fit np and pp scattering data very
accurately. The potential models we employ are the recent versions of the
Nijmegen group, Nijm-I, Nijm-II and Reid93, the Argonne potential and
the CD-Bonn potential. All these potentials yield a symmetry energy which
increases with density, resolving a discrepancy that existed for older NN
potentials. The origin of remaining differences is discussed.Comment: 17 pages, 10 figures included, elsevier latex style epsart.st
Relativistic Structure of the Nucleon Self-Energy in Asymmetric Nuclei
The Dirac structure of the nucleon self-energy in asymmetric nuclear matter
cannot reliably be deduced from the momentum dependence of the single-particle
energies. It is demonstrated that such attempts yield an isospin dependence
with even a wrong sign. Relativistic studies of finite nuclei have been based
on such studies of asymmetric nuclear matter. The effects of these isospin
components on the results for finite nuclei are investigated.Comment: 9 pages, Latex 4 figures include
Muons and emissivities of neutrinos in neutron star cores
In this work we consider the role of muons in various URCA processes relevant
for neutrino emissions in the core region of neutron stars. The calculations
are done for --stable nuclear matter with and without muons. We find
muons to appear at densities fm, slightly around the
saturation density for nuclear matter fm. The direct URCA
processes for nucleons are forbidden for densities below
fm, however the modified URCA processes with muons ), where is a
nucleon, result in neutrino emissivities comparable to those from
). This
opens up for further possibilities to explain the rapid cooling of neutrons
stars. Superconducting protons reduce however these emissivities at densities
below fm.Comment: 14 pages, Revtex style, 3 uuencoded figs include
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
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