2,174 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 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
Super-Symmetry transformation for excitation processes
Quantum Mechanics SUper-SYmmetry (QM-SUSY) provides a general framework for
studies using phenomenological potentials for nucleons (or clusters)
interacting with a core. The SUSY potentials result from the transformation of
the mean field potential in order to account for the Pauli blocking of the core
orbitals. In this article, we discuss how other potentials (like external
probes or residual interactions between the valence nucleons) are affected by
the SUSY transformation. We illustrate how the SUSY transformations induce
off-diagonal terms in coordinate space that play the essential role on the
induced transition probabilities on two examples: the electric operators and
Gaussian external fields. We show that excitation operators, doorway states,
strength and sum rules are modified.Comment: 14 pages, 13 figure
On the maximum mass of hyperonic neutron stars
Chiral Lagrangian and quark-meson coupling models of hyperon matter are used
to estimate the maximum mass of neutron stars. Our relativistic calculations
include, for the first time, both Hartree and Fock contributions in a
consistent manner. Being related to the underlying quark structure of baryons,
these models are considered to be good candidates for describing the dense core
of neutron stars. Taking account of the known experimental constraints at
saturation density, the equations of state deduced from these relativistic
approaches cannot sustain a neutron star with a mass larger than 1.6-1.66
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
Neutrino propagation in dense hadronic matter
Neutrino propagation in protoneutron stars requires the knowledge of the
composition as well as the dynamical response function of dense hadronic
matter. Matter at very high densities is probably composed of other particles
than nucleons and little is known on the Fermi liquid properties of hadronic
multicomponent systems. We will discuss the effects that the presence of
hyperons might have on the response and, in particular, on its
influence on the thermodynamical stability of the system and the mean free path
of neutrinos in dense matter.Comment: Proceedings of the XX Max Born Symposium ''Nuclear effects in
neutrino interactions'', Wroclaw (Poland), December 7-10, 200
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
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