682 research outputs found
Extended Skyrme interaction (II): ground state of nuclei and of nuclear matter
We study the effect of time-odd components of the Skyrme energy density
functionals on the ground state of finite nuclei and in nuclear matter. The
spin-density dependent terms, which have been recently proposed as an extension
of the standard Skyrme interaction, are shown to change the total binding
energy of odd-nuclei by only few tenths of keV, while the time-odd components
of standard Skyrme interactions give an effect that is larger by one order of
magnitude. The HFB-17 mass formula based on a Skyrme parametrization is
adjusted including the new spin-density dependent terms. A comprehensive study
of binding energies in the whole mass table of 2149 nuclei gives a root mean
square (rms) deviation of 0.575 MeV between experimental data and the
calculated results, which is slightly better than the original HFB-17 mass
formula. From the analysis of the spin instabilities of nuclear matter,
restrictions on the parameters governing the spin-density dependent terms are
evaluated. We conclude that with the extended Skyrme interaction, the Landau
parameters and could be tuned with a large flexibility
without changing the ground-state properties in nuclei and in nuclear matter.Comment: 18 pages, 4 tables, 6 figure
The neutron star inner crust and symmetry energy
The cell structure of clusters in the inner crust of a cold \beta-equilibrium
neutron star is studied within a Thomas Fermi approach and compared with other
approaches which include shell effects. Relativistic nuclear models are
considered. We conclude that the symmetry energy slope L may have quite
dramatic effects on the cell structure if it is very large or small. Rod-like
and slab-like pasta clusters have been obtained in all models except one with a
large slope L.Comment: 16 pages, 5 figure
On the validity of the Wigner-Seitz approximation in neutron star crust
The inner crust of neutron stars formed of nuclear clusters immersed in a
neutron sea has been widely studied in the framework of the Wigner-Seitz
approximation since the seminal work of Negele and Vautherin. In this article,
the validity of this approximation is discussed in the framework of the band
theory of solids. For a typical cell of Zr, present in the external
layers of the inner crust, it is shown that the ground state properties of the
neutron gas are rather well reproduced by the Wigner-Seitz approximation, while
its dynamical properties depend on the energy scale of the process of interest
or on the temperature. It is concluded that the Wigner-Seitz approximation is
well suited for describing the inner crust of young neutron stars and the
collapsing core of massive stars during supernovae explosions. However the band
theory is required for low temperature fluid dynamics.Comment: 7 pages, with figures - PTH, version
Further explorations of Skyrme-Hartree-Fock-Bogoliubov mass formulas. IX: Constraint of pairing force to neutron-matter gap
In this latest of our series of Skyrme-HFB mass models, HFB-16, we introduce
the new feature of requiring that the contact pairing force reproduce at each
density the pairing gap of neutron matter as determined in microscopic
calculations with realistic nucleon-nucleon forces. We retain the earlier
constraints on the Skyrme force of reproducing the energy-density curve of
neutron matter, and of having an isoscalar effective mass of in
symmetric infinite nuclear matter at the saturation density; we also keep the
recently adopted device of dropping Coulomb exchange. Furthermore, the
correction term for the spurious energy of collective motion has a form that is
known to favour fission barriers that are in good agreement with experiment.
Despite the extra constraints on the effective force, we have achieved a better
fit to the mass data than any other mean field model, the rms error on the 2149
measured masses of nuclei with and 8 having been reduced to 0.632
MeV; the improvement is particularly striking for the most neutron-rich nuclei.
Moreover, it turns out that even with no flexibility at all remaining for the
pairing force, the spectral pairing gaps that we find suggest that level
densities in good agreement with experiment should be obtained. This new force
is thus particularly well-suited for astrophysical applications, such as
stellar nucleosynthesis and neutron-star crusts.Comment: 38 pages, 9 figures accepted for publication in Nuclear Physics
A Cosmic Census of Radio Pulsars with the SKA
The Square Kilometre Array (SKA) will make ground breaking discoveries in
pulsar science. In this chapter we outline the SKA surveys for new pulsars, as
well as how we will perform the necessary follow-up timing observations. The
SKA's wide field-of-view, high sensitivity, multi-beaming and sub-arraying
capabilities, coupled with advanced pulsar search backends, will result in the
discovery of a large population of pulsars. These will enable the SKA's pulsar
science goals (tests of General Relativity with pulsar binary systems,
investigating black hole theorems with pulsar-black hole binaries, and direct
detection of gravitational waves in a pulsar timing array). Using SKA1-MID and
SKA1-LOW we will survey the Milky Way to unprecedented depth, increasing the
number of known pulsars by more than an order of magnitude. SKA2 will
potentially find all the Galactic radio-emitting pulsars in the SKA sky which
are beamed in our direction. This will give a clear picture of the birth
properties of pulsars and of the gravitational potential, magnetic field
structure and interstellar matter content of the Galaxy. Targeted searches will
enable detection of exotic systems, such as the ~1000 pulsars we infer to be
closely orbiting Sgr A*, the supermassive black hole in the Galactic Centre. In
addition, the SKA's sensitivity will be sufficient to detect pulsars in local
group galaxies. To derive the spin characteristics of the discoveries we will
perform live searches, and use sub-arraying and dynamic scheduling to time
pulsars as soon as they are discovered, while simultaneously continuing survey
observations. The large projected number of discoveries suggests that we will
uncover currently unknown rare systems that can be exploited to push the
boundaries of our understanding of astrophysics and provide tools for testing
physics, as has been done by the pulsar community in the past.Comment: 20 pages, 7 figures, to be published in: "Advancing Astrophysics with
the Square Kilometre Array", Proceedings of Science, PoS(AASKA14)04
Phase diagram of neutron-rich nuclear matter and its impact on astrophysics
Dense matter as it can be found in core-collapse supernovae and neutron stars
is expected to exhibit different phase transitions which impact the matter
composition and equation of state, with important consequences on the dynamics
of core-collapse supernova explosion and on the structure of neutron stars. In
this paper we will address the specific phenomenology of two of such
transitions, namely the crust-core solid-liquid transition at sub-saturation
density, and the possible strange transition at super-saturation density in the
presence of hyperonic degrees of freedom. Concerning the neutron star
crust-core phase transition at zero and finite temperature, it will be shown
that, as a consequence of the presence of long-range Coulomb interactions, the
equivalence of statistical ensembles is violated and a clusterized phase is
expected which is not accessible in the grand-canonical ensemble. A specific
quasi-particle model will be introduced to illustrate this anomalous
thermodynamics and some quantitative results relevant for the supernova
dynamics will be shown. The opening of hyperonic degrees of freedom at higher
densities corresponding to the neutron stars core modifies the equation of
state. The general characteristics and order of phase transitions in this
regime will be analyzed in the framework of a self-consistent mean-field
approach.Comment: Invited Talk given at the 11th International Conference on
Nucleus-Nucleus Collisions (NN2012), San Antonio, Texas, USA, May 27-June 1,
2012. To appear in the NN2012 Proceedings in Journal of Physics: Conference
Series (JPCS
Instabilities of infinite matter with effective Skyrme-type interactions
The stability of the equation of state predicted by Skyrme-type interactions
is examined. We consider simultaneously symmetric nuclear matter and pure
neutron matter. The stability is defined by the inequalities that the Landau
parameters must satisfy simultaneously. A systematic study is carried out to
define interaction parameter domains where the inequalities are fulfilled. It
is found that there is always a critical density beyond which the
system becomes unstable. The results indicate in which parameter regions one
can find effective forces to describe correctly finite nuclei and give at the
same time a stable equation of state up to densities of 3-4 times the
saturation density of symmetric nuclear matter.Comment: 20 pages, 5 figures, submitted to Phys.Rev.
Bimodality and Coulomb effects with a canonical thermodynamic model
The effect of the Coulomb interaction on the phase diagram of finite nuclei
is studied within the Canonical Thermodynamic Model. If Coulomb effects are
artificially switched off, this model shows a phenomenology consistent with the
liquid-gas phase transition. The inclusion of Coulomb does not significantly
affect the phase diagram but it drastically modifies the nature and order
parameter of the transition. A clear understanding of the phenomenon can be
achieved looking at the distribution of the largest fragment produced in each
fragmentation event. Possible connections with experimental observations are
outlined.Comment: Submitted to NP
Neutrino mean free paths in spin-polarized neutron Fermi liquids
Neutrino mean free paths in magnetized neutron matter are calculated using
the Hartree-Fock approximation with effective Skyrme and Gogny forces in the
framework of the Landau Fermi Liquid Theory. It is shown that describing
nuclear interaction with Skyrme forces and for magnetic field strengths
, the neutrino mean free paths stay almost unchanged
at intermediate densities but they largely increase at high densities when they
are compared to the field-free case results. However the description with Gogny
forces differs from the previous and mean free paths stay almonst unchanged or
decrease at densities . This different behaviour can be explained
due to the combination of common mild variation of the Landau parameters with
both types of forces and the values of the nucleon effective mass and induced
magnetization of matter under presence of a strong magnetic field as described
with the two parametrizations of the nuclear interaction.Comment: 9 pages, 3 figure
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