74 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
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
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
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
Isospin symmetry breaking nucleon-nucleon potentials and nuclear structure
Modern nucleon-nucleon (NN) potentials, which accurately fit the
nucleon-nucleon scattering phase shifts, contain terms which break isospin
symmetry. The effects of these symmetry violating terms on the bulk properties
of nuclear matter are investigated. The predictions of the charge symmetry
breaking (CSB) terms are compared with the Nolen-Schiffer (NS) anomaly
regarding the energies of neighboring mirror nuclei. We find that, for a
quantitative explanation of the NS anomaly, it is crucial to include CSB in
partial waves with (besides ) as derived from a microscopic model
for CSB of the NN interaction.Comment: 14 pages, RevTex, 2 figure
Phaseshift equivalent NN potentials and the deuteron
Different modern phase shift equivalent NN potentials are tested by
evaluating the partial wave decomposition of the kinetic and potential energy
of the deuteron. Significant differences are found, which are traced back to
the matrix elements of the potentials at medium and large momenta. The
influence of the localisation of the one-pion-exchange contribution to these
potentials is analyzed in detail.Comment: 11 pages, LaTeX, 4 figures include
Relativistic Equation of State of Nuclear Matter for Supernova and Neutron Star
We construct the equation of state (EOS) of nuclear matter using the
relativistic mean field (RMF) theory in the wide density, temperature range
with various proton fractions for the use of supernova simulation and the
neutron star calculations. We first construct the EOS of homogeneous nuclear
matter. We use then the Thomas-Fermi approximation to describe inhomogeneous
matter, where heavy nuclei are formed together with free nucleon gas. We
discuss the results on free energy, pressure and entropy in the wide range of
astrophysical interest. As an example, we apply the resulting EOS on the
neutron star properties by using the Oppenheimer-Volkoff equation.Comment: 15 pages, LaTeX, 14 ps-figures, accepted for publication in
Nucl.Phys.
Modern nucleon-nucleon interactions and charge-symmetry breaking in nuclei
Coulomb displacement energies, i.e., the differences between the energies of
corresponding nuclear states in mirror nuclei, are evaluated using recent
models for the nucleon-nucleon (NN) interaction. These modern NN potentials
account for breaking of isospin symmetry and reproduce and phase
shifts accurately. The predictions by these new potentials for the binding of
are calculated. A particular focus of our study are effects due to
nuclear correlations and charge-symmetry breaking (CSB). We find that the CSB
terms in the modern NN interactions substantially reduce the discrepancy
between theory and experiment for the Coulomb displacement energies; however,
our calculations do not completely explain the Nolen-Schiffer anomaly.
Potential sources for the remaining discrepancies are discussed.Comment: 10 pages RevTeX, no figure
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
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
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