209 research outputs found
Effect of the -meson on the instabilities of nuclear matter under strong magnetic fields
We study the influence of the isovector-scalar meson on the spinodal
instabilities and the distillation effect in asymmetric non-homogenous nuclear
matter under strong magnetic fields, of the order of G.
Relativistic nuclear models both with constant couplings (NLW) and with density
dependent parameters (DDRH) are considered. A strong magnetic field can have
large effects on the instability regions giving rise to bands of instability
and wider unstable regions. It is shown that for neutron rich matter the
inclusion of the meson increases the size of the instability region
for NLW models and decreases it for the DDRH models. The effect of the
meson on the transition density to homogeneous -equilibrium matter is
discussed. The DDRH model predicts the smallest transition pressures,
about half the values obtained for NL.Comment: 6 pages, 5 figues, 3 tables, accepted for publication in Phys. Rev.
Color symmetrical superconductivity in a schematic nuclear quark model
In this note, a novel BCS-type formalism is constructed in the framework of a
schematic QCD inspired quark model, having in mind the description of color
symmetrical superconducting states. The physical properties of the BCS vacuum
(average numbers of quarks of different colors) remain unchanged under an
arbitrary color rotation. In the usual approach to color superconductivity, the
pairing correlations affect only the quasi-particle states of two colors, the
single particle states of the third color remaining unaffected by the pairing
correlations. In the theory of color symmetrical superconductivity here
proposed, the pairing correlations affect symmetrically the quasi-particle
states of the three colors and vanishing net color-charge is automatically
insured. It is found that the groundstate energy of the color symmetrical
sector of the Bonn model is well approximated by the average energy of the
color symmetrical superconducting state proposed here
Hyperons in neutron star matter within relativistic mean-field models
Since the discovery of neutron stars with masses around 2 solar masses the
composition of matter in the central part of these massive stars has been
intensively discussed. Within this paper we will (re)investigate the question
of the appearance of hyperons. To that end we will perform an extensive
parameter study within relativistic mean field models. We will show that it is
possible to obtain high mass neutron stars (i) with a substantial amount of
hyperons, (ii) radii of 12-13 km for the canonical mass of 1.4 solar masses,
and (iii) a spinodal instability at the onset of hyperons. The results depend
strongly on the interaction in the hyperon-hyperon channels, on which only very
little information is available from terrestrial experiments up to now.Comment: 15 pages, 10 figure
Dynamical instabilities in density-dependent hadronic relativistic models
Unstable modes in asymmetric nuclear matter (ANM) at subsaturation densities
are studied in the framework of relativistic mean-field density-dependent
hadron models. The size of the instabilities that drive the system are
calculated and a comparison with results obtained within the non-linear Walecka
model is presented. The distillation and anti-distillation effects are
discussed.Comment: 8 pages, 8 Postscript figures. Submitted for publication in Phys.
Rev.
Aspects of short range correlations in a relativistic model
In the present work short range correlations are introduced for the first
time in a relativistic approach to the equation of state of the infinite
nuclear matter in the framework of the Hartree-Fock approximation using an
effective Hamiltonian derived from the Walecka model. The
unitary correlation method is used to introduce short range correlations. The
effect of the correlations in the ground state properties of the nuclear matter
is discussed.Comment: 7 pages, 3 figure
Nuclear symmetry energy and core-crust transition in neutron stars: a critical study
The slope of the nuclear symmetry energy at saturation density is pointed
out as a crucial quantity to determine the mass and width of neutron-star
crusts. This letter clarifies the relation between and the core-crust
transition. We confirm that the transition density is soundly correlated with
despite differences between models, and we propose a clear understanding of
this correlation based on a generalised liquid drop model. Using a large number
of nuclear models, we evaluate the dispersion affecting the correlation between
the transition pressure and . From a detailed analysis it is shown
that this correlation is weak due to a cancellation between different terms.
The correlation between the isovector coefficients and plays
a crucial role in this discussion
Mean-filed theories with mixed states and associated boson expansions
A variational derivation of the Liouville-von Neumann equation of quantum-statistical mechanics is presented, in order to formulate mean-field approximations appropriate to mixed states. The Hartree-Fock and the RPA at finite temperatures are particular cases of the general formalism. A thermal boson expansion is defined, which allows us to describe anharmonic motion around a thermal excited state. In a numerical application on the basis of the Lipkin model, temperature-dependent phase transitions are observed
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