31 research outputs found
Pairing: from atomic nuclei to neutron-star crusts
Nuclear pairing is studied both in atomic nuclei and in neutron-star crusts
in the unified framework of the energy-density functional theory using
generalized Skyrme functionals complemented with a local pairing functional
obtained from many-body calculations in homogeneous nuclear matter using
realistic forces.Comment: 16 pages, 3 figures. Contribution for the book "50 years of nuclear
BCS", edited by R.A. Broglia and V. Zelevinsk
Superfluidity and entrainment in neutron-star crusts
Despite the absence of viscous drag, the neutron superfluid permeating the
inner crust of a neutron star can still be strongly coupled to nuclei due to
non-dissipative entrainment effects. Neutron superfluidity and entrainment have
been systematically studied in all regions of the inner crust of a cold
non-accreting neutron star in the framework of the band theory of solids. It is
shown that in the intermediate layers of the inner crust a large fraction of
"free" neutrons are actually entrained by the crust. The results suggest that a
revision of the interpretation of many observable astrophysical phenomena might
be necessary.Comment: 4 pages, to appear in the proceedings of the ERPM conference, Zielona
Gora, Poland, April 201
Breathing-mode measurements in Sn isotopes and isospin dependence of nuclear incompressibility
T. Li {\it et al.}[Phys. Rev. C {\bf 81}, 034309 (2010)] have analyzed their
measured breathing-mode energies of some tin isotopes in terms of a first-order
leptodermous expansion, and find for the symmetry-incompressibility coefficient
the value of -550 100 MeV. Removing an approximation that they
made, we find that the first-order estimate of shifts to -661
144 MeV. However, taking into account higher-order terms in the leptodermous
expansion shows that the data are compatible with the significantly lower
magnitudes indicated by both another experiment and some theoretical estimates.Comment: 6 pages, 1 figur
Skyrme-Hartree-Fock-Bogoliubov nuclear mass formulas: Crossing the 0.6 MeV threshold with microscopically deduced pairing
We present a new Skyrme-Hartree-Fock-Bogoliubov nuclear-mass model in which
the contact-pairing force is constructed from microscopic pairing gaps of
symmetric nuclear matter and neutron matter calculated from realistic two- and
three-body forces, with medium-polarization effects included. With the pairing
being treated more realistically than in any of our earlier models, the rms
deviation with respect to essentially all the available mass data falls to
0.581 MeV, the best value ever found within the mean-field framework. Since our
Skyrme force is also constrained by the properties of pure neutron matter, this
new model is particularly well suited for application to astrophysical problems
involving a neutron-rich environment, such as the elucidation of the r process
of nucleosynthesis, and the description of supernova cores and neutron-star
crusts
Structure of neutron stars with unified equations of state
We present a set of three unified equations of states (EoSs) based on the
nuclear energy-density functional (EDF) theory.These EoSs are based on
generalized Skyrme forces fitted to essentially all experimental atomic mass
data and constrained to reproduce various properties of infinite nuclear matter
as obtained from many-body calculations using realistic two- and three-body
interactions. The structure of cold isolated neutron stars is discussed in
connection with some astrophysical observations.Comment: 4 pages, to appear in the proceedings of the ERPM conference, Zielona
Gora, Poland, April 201
Symmetry energy: nuclear masses and neutron stars
We describe the main features of our most recent Hartree-Fock-Bogoliubov
nuclear mass models, based on 16-parameter generalized Skyrme forces. They have
been fitted to the data of the 2012 Atomic Mass Evaluation, and favour a value
of 30 MeV for the symmetry coefficient J, the corresponding root-mean square
deviation being 0.549 MeV. We find that this conclusion is compatible with
measurements of neutron-skin thickness. By constraining the underlying
interactions to fit various equations of state of neutron matter calculated
{\it ab initio} our models are well adapted to a realistic and unified
treatment of all regions of neutron stars. We use our models to calculate the
composition, the equation of state, the mass-radius relation and the maximum
mass. Comparison with observations of neutron stars again favours a value of J
= 30 MeV.Comment: 10 pages, 9 figures, to appear in EPJA special volume on symmetry
energ
Further explorations of Skyrme-Hartree-Fock-Bogoliubov mass formulas. XI: Stabilizing neutron stars against a ferromagnetic collapse
We construct a new Hartree-Fock-Bogoliubov (HFB) mass model, labeled HFB-18,
with a generalized Skyrme force. The additional terms that we have introduced
into the force are density-dependent generalizations of the usual and
terms, and are chosen in such a way as to avoid the high-density
ferromagnetic instability of neutron stars that is a general feature of
conventional Skyrme forces, and in particular of the Skyrme forces underlying
all the HFB mass models that we have developed in the past. The remaining
parameters of the model are then fitted to essentially all the available mass
data, an rms deviation of 0.585 MeV being obtained. The new model thus
gives almost as good a mass fit as our best-fit model HFB-17 ( = 0.581
MeV), and has the advantage of avoiding the ferromagnetic collapse of neutron
stars.Comment: accepted for publication in Physical Review
Recent breakthroughs in Skyrme-Hartree-Fock-Bogoliubov mass formulas
We review our recent achievements in the construction of microscopic mass
tables based on the Hartree-Fock-Bogoliubov method with Skyrme effective
interactions. In the latest of our series of HFB-mass models, we have obtained
our best fit ever to essentially all the available mass data, by treating the
pairing more realistically than in any of our earlier models. The rms deviation
on the 2149 measured masses of nuclei with N and Z>8 has been reduced for the
first time in a mean field approach to 0.581 MeV. With the additional
constraint on the neutron-matter equation of state, this new force is thus very
well-suited for the study of neutron-rich nuclei and for the description of
astrophysical environments like supernova cores and neutron-star crusts.Comment: Proceedings of the Fifth International Conference on Exotic Nuclei
and Atomic Masses, September 7-13 2008, Ryn (Poland). To appear in the
European Physical Journal
Masses of neutron stars and nuclei
We calculate the maximum mass of neutron stars for three different equations
of state (EOS) based on generalized Skyrme functionals that are simultaneously
fitted to essentially all the 2003 nuclear mass data (the rms deviation is 0.58
MeV in all three cases) and to one or other of three different equations of
state of pure neutron matter, each determined by a different many-body
calculation using realistic two- and three-body interactions but leading to
significantly different degrees of stiffness at the high densities prevailing
in neutron-star interiors. The observation of a neutron star with mass 1.97
0.04 eliminates the softest of our models (BSk19),
but does not discriminate between BSk20 and BSk21. However, nuclear-mass
measurements that have been made since our models were constructed strongly
favor BSk21, our stiffest functional.Comment: 11 pages, 4 figures; Physical Review C in pres
Further explorations of Skyrme-Hartree-Fock-Bogoliubov mass formulas. XII: Stiffness and stability of neutron-star matter
We construct three new Hartree-Fock-Bogoliubov (HFB) mass models, labeled
HFB-19, HFB-20, and HFB-21, with unconventional Skyrme forces containing
and terms, i.e., density-dependent generalizations of the usual and
terms, respectively. The new forces underlying these models are fitted
respectively to three different realistic equations of state of neutron matter
for which the density dependence of the symmetry energy ranges from the very
soft to the very stiff, reflecting thereby our present lack of complete
knowledge of the high-density behavior of nuclear matter. All unphysical
instabilities of nuclear matter, including the transition to a polarized state
in neutron-star matter, are eliminated with the new forces. At the same time
the new models fit essentially all the available mass data with rms deviations
of 0.58 MeV and give the same high quality fits to measured charge radii that
we obtained in earlier models with conventional Skyrme forces. Being
constrained by neutron matter, these new mass models, which all give similar
extrapolations out to the neutron drip line, are highly appropriate for studies
of the -process and the outer crust of neutron stars. Moreover, the
underlying forces, labeled BSk19, BSk20 and BSk21, respectively, are well
adapted to the study of the inner crust and core of neutron stars. The new
family of Skyrme forces thus opens the way to a unified description of all
regions of neutron stars.Comment: 45 pages, 16 figures, accepted for publication in Physical Review