823 research outputs found

### Neutrino mean free path and in-medium nuclear interaction

Neutrinos produced during the collapse of a massive star are trapped in a
nuclear medium (the proto-neutron star). Typically, neutrino energies (10-100
MeV) are of the order of nuclear giant resonances energies. Hence, neutrino
propagation is modified by the possibility of coherent scattering on nucleons.
We have compared the predictions of different nuclear interaction models. It
turns out that their main discrepancies are related to the density dependence
of the k-effective mass as well as to the onset of instabilities as density
increases. This last point had led us to a systematic study of instabilities of
infinite matter with effective Skyrme-type interactions. We have shown that for
such interactions there is always a critical density, above which the system
becomes unstable.Comment: 4 pages, 4 figures, Proceedings of the 17th Divisional Conference on
Nuclear Physics in Astrophysics (NPDC17), 30th September - 4th October 2002,
ATOMKI, Debrecen, Hungary, to appear in Nuclear Physics

### 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 $G_0$ and $G_0^\prime$ 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

### Extended Skyrme interaction (I): spin fluctuations in dense matter

Most of the Skyrme interactions are known to predict spin or isospin
instabilities beyond the saturation density of nuclear matter which contradict
predictions based on realistic interactions. A modification of the standard
Skyrme interaction is proposed so that the ferromagnetic instability is
removed. The new terms are density dependent and modify only the spin p-h
interaction in the case of spin-saturated system. Consequences for the nuclear
response function and neutrino mean free path are shown. The overall effect of
the RPA correlations makes dense matter more transparent for neutrino
propagation by a factor of 2 to 10 depending of the density.Comment: 6 pages, 5 Figs., 2 Tab

### Analytical mass formula and nuclear surface properties in the ETF approximation

The problem of the determination of the nuclear surface and surface symmetry
energy is addressed in the framework of the Extended Thomas Fermi (ETF)
approximation using Skyrme functionals. We propose an analytical model for the
density profiles with variationally determined diffuseness parameters. For the
case of symmetric nuclei, the resulting ETF functional can be exactly
integrated, leading to an analytical formula expressing the surface energy as a
function of the couplings of the energy functional. The importance of non-local
terms is stressed, which cannot be simply deduced from the local part of the
functional. In the case of asymmetric nuclei, we propose an approximate
expression for the diffuseness and the surface energy. These quantities are
analytically related to the parameters of the energy functional. In particular,
the influence of the different equation of state parameters can be explicitly
quantified. Detailed analyses of the different energy components
(local/non-local, isoscalar/isovector, surface/curvature and higher order) are
also performed. Our analytical solution of the ETF integral improves over
previous models and leads to a precision better than 200 keV per nucleon in the
determination of the nuclear binding energy for dripline nuclei.Comment: 27 pages, 18 figures, submitted to PR

### Neutrino propagation in Neutron Matter and the Nuclear Equation of State

We study the propagation of neutrinos inside dense matter under the
conditions prevailing in a proto-neutron star. Equations of state obtained with
different nuclear effective interactions (Skyrme type and Gogny type) are first
discussed. It is found that for many interactions, spin and/or isospin
instabilities occur at densities larger than the saturation density of nuclear
matter. From this study we select two representative interactions, SLy230b and
D1P. We calculate the response functions in pure neutron matter where nuclear
correlations are described at the Hartree-Fock plus RPA level. These response
functions allow us to evaluate neutrino mean free paths corresponding to
neutral current processes.Comment: 8 pages, 7 figures, to appear in "The Nuclear Many-Body Problem
2001", NATO Science Series II (Kluwer Academic Publishers

### Can realistic interaction be useful for nuclear mean-field approaches?

Recent applications of the M3Y-type semi-realistic interaction to the nuclear
mean-field approaches are presented: (i) Prediction of magic numbers and (ii)
isotope shifts of nuclei with magic proton numbers. The results exemplify that
realistic interaction, which is derived from the base $2N$ and $3N$
interaction, furnish a new theoretical instrument for advancing nuclear
mean-field approaches.Comment: 9 pages including 6 figures, published in EPJA 52, 185 (2016

### 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

### Densities and energies of nuclei in dilute matter

We explore the ground-state properties of nuclear clusters embedded in a gas
of nucleons with the help of Skyrme-Hartree-Fock microscopic calculations. Two
alternative representations of clusters are introduced, namely coordinate-space
and energy-space clusters. We parameterize their density profiles in spherical
symmetry in terms of basic properties of the energy density functionals used
and propose an analytical, Woods-Saxon density profile whose parameters depend,
not only on the composition of the cluster, but also of the nucleon gas. We
study the clusters' energies with the help of the local-density approximation,
validated through our microscopic results. We find that the volume energies of
coordinate-space clusters are determined by the saturation properties of
matter, while the surface energies are strongly affected by the presence of the
gas. We conclude that both the density profiles and the cluster energies are
strongly affected by the gas and discuss implications for the nuclear EoS and
related perspectives. Our study provides a simple, but microscopically
motivated modeling of the energetics of clusterized matter at subsaturation
densities, for direct use in consequential applications of astrophysical
interest.Comment: 20 pages, incl. 12 figure

### Spin-isospin Response in Finite Nuclei from an Extended Skyrme Interaction

The magnetic dipole (M1) and the Gamow-Teller (GT) excitations of finite
nuclei have been studied in a fully self-consistent Hartree-Fock (HF) plus
random phase approximation (RPA) approach by using a Skyrme energy density
functional with spin and spin-isospin densities. To this end, we adopt the
extended SLy5st interaction which includes spin-density dependent terms and
stabilize nuclear matter with respect to spin instabilities. The effect of the
spin-density dependent terms is examined in both the mean field and the
spin-flip excited state calculations. The numerical results show that those
terms give appreciable repulsive contributions to the M1 and GT response
functions of finite nuclei.Comment: 6 pages, 2 figure

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