741 research outputs found
Momentum, Density, and Isospin dependence of the Symmetric and Asymmetric Nuclear Matter Properties
Properties of symmetric and asymmetric nuclear matter have been investigated
in the relativistic Dirac-Brueckner-Hartree-Fock approach based on projection
techniques using the Bonn A potential. The momentum, density, and isospin
dependence of the optical potentials and nucleon effective masses are studied.
It turns out that the isovector optical potential depends sensitively on
density and momentum, but is almost insensitive to the isospin asymmetry.
Furthermore, the Dirac mass and the nonrelativistic mass
which parametrizes the energy dependence of the single particle spectrum, are
both determined from relativistic Dirac-Brueckner-Hartree-Fock calculations.
The nonrelativistic mass shows a characteristic peak structure at momenta
slightly above the Fermi momentum \kf. The relativistic Dirac mass shows a
proton-neutron mass splitting of in isospin asymmetric
nuclear matter. However, the nonrelativistic mass has a reversed mass splitting
which is in agreement with the results from
nonrelativistic calculations.Comment: 25 pages, 12 figures, to appear in Physical Review
Spinodal Instabilities in Asymmetric Nuclear Matter Based on Realistic Interactions
A density dependent relativistic mean-field model is determined to reproduce
the components of the nucleon self-energy at low densities. This model is used
to investigate spinodal instabilities in isospin asymmetric nuclear matter at
finite temperatures. The inhomogeneous density distributions in the spinodal
region are investigated through calculations in a cubic Wigner-Seitz cell.
Compared to results obtained in phenomenological calculations the spinodal
region is large, i.e. the spinodal region at zero temperature can reach
densities above 0.12 fm. The predicted spinodal region is concentrated
around isospin symmetric nuclear matter and the critical temperature is
considerably lower than in the previous microscopic based investigation within
a non-relativistic Brueckner-Hartree-Fock approach.Comment: 11 pages, 7 figure
Dirac-Brueckner-Hartree-Fock calculations for isospin asymmetric nuclear matter based on improved approximation schemes
We present Dirac-Brueckner-Hartree-Fock calculations for isospin asymmetric
nuclear matter which are based on improved approximations schemes. The
potential matrix elements have been adapted for isospin asymmetric nuclear
matter in order to account for the proton-neutron mass splitting in a more
consistent way. The proton properties are particularly sensitive to this
adaption and its consequences, whereas the neutron properties remains almost
unaffected in neutron rich matter. Although at present full Brueckner
calculations are still too complex to apply to finite nuclei, these
relativistic Brueckner results can be used as a guidance to construct a density
dependent relativistic mean field theory, which can be applied to finite
nuclei. It is found that an accurate reproduction of the
Dirac-Brueckner-Hartree-Fock equation of state requires a renormalization of
these coupling functions.Comment: 34 pages, 9 figures, submitted to Eur. Phys. J.
Model independent study of the Dirac structure of the nucleon-nucleon interaction
Relativistic and non-relativistic modern nucleon-nucleon potentials are
mapped on a relativistic operator basis using projection techniques. This
allows to compare the various potentials at the level of covariant amplitudes
were a remarkable agreement is found. In nuclear matter large scalar and vector
mean fields of several hundred MeV magnitude are generated at tree level. This
is found to be a model independent feature of the nucleon-nucleon interaction.Comment: 5 pages, 2 figures, results for V_lowk added, to appear in PR
Bulk Viscosity in Neutron Stars from Hyperons
The contribution from hyperons to the bulk viscosity of neutron star matter
is calculated. Compared to previous works we use for the weak interaction the
one-pion exchange model rather than a current-current interaction, and include
the neutral current process. Also the sensitivity
to details of the equation of state is examined. Compared to previous works we
find that the contribution from hyperons to the bulk viscosity is about two
orders of magnitude smaller.Comment: 18 pages, to appear in Physical Review
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