2,354 research outputs found
Constraints, limits and extensions for nuclear energy functionals
In the present contribution, we discuss the behavior of Skyrme forces when
they are employed to study both neutron stars and giant resonance states in
208Pb within the fully self-consistent Random Phase Approximation (RPA). We
point out that clear correlations exist between the results for the isoscalar
monopole and isovector dipole resonances (ISGMR and IVGDR), and definite
quantities which characterize the equation of state (EOS) of uniform matter. We
propose that the RPA results or, to some extent, the mentioned EOS parameters,
are used as constraints when a force is fitted. This suggestion can be valid
also when the fit of a more general energy density functional is envisaged. We
use our considerations to select a limited number of Skyrme forces (10) out of
a large sample of 78 interactions.Comment: To appear in the Proceedings of the 5th ANL/MSU/JINA/INT FRIB
Workshop on Bulk Nuclear Properties, Michigan State University, East Lansing
(USA), November 19-22, 200
Theoretical understanding of the nuclear incompressibility: where do we stand ?
The status of the theoretical research on the compressional modes of finite
nuclei and the incompressibility of nuclear matter, is reviewed. It
is argued that the recent experimental data on the Isoscalar Giant Monopole
Resonance (ISGMR) allow extracting the value of with an uncertainity
of about 12 MeV. Non-relativistic (Skyrme, Gogny) and relativistic mean
field models predict for values which are significantly different
from one another, namely 220-235 and 250-270 MeV
respectively. It is shown that the solution of this puzzle requires a better
determination of the symmetry energy at, and around, saturation. The role
played by the experimental data of the Isoscalar Giant Dipole Resonance (ISGDR)
is also discussed.Comment: To appear in the proceedings of the COMEX1 conference (special issue
of Nucl. Phys. A). Few changes and corrections compared to the previous
version. General conclusion unchange
Microscopic linear response calculations based on the Skyrme functional plus the pairing contribution
A self-consistent Quasiparticle-Random-Phase-Approximation (QRPA) model which
employs the canonical Hartree-Fock-Bogoliubov (HFB) basis and an energy-density
functional with a Skyrme mean field part and a density-dependent pairing, is
used to study the monopole collective excitations of spherical even-even
nuclei. The influence of the spurious state on the strength function of the
isoscalar monopole excitations is clearly assessed. We compare the effect of
different kinds of pairing forces (volume pairing, surface pairing and mixed
pairing) on the monopole excitation strength function. The energy of the
Isoscalar Giant Monopole Resonance (ISGMR), which is related to the nuclear
incompressibility , is calculated for tin isotopes and the results
are discussed.Comment: Accepted for publication in Phys. Rev.
Gamow-Teller response and its spreading mechanism in doubly magic nuclei
The scope of the paper is to apply a state-of-the-art beyond mean-field model
to the description of the Gamow-Teller response in atomic nuclei. This topic
recently attracted considerable renewed interest, due, in particular, to the
possibility of performing experiments in unstable nuclei. We study the cases of
Ca, Ni, Sn and Pb. Our model is based on a fully
self-consistent Skyrme Hartree-Fock plus random phase approximation. The same
Skyrme interaction is used to calculate the coupling between particles and
vibrations, which leads to the mixing of the Gamow-Teller resonance with a set
of doorway states and to its fragmentation. We compare our results with
available experimental data. The microscopic coupling mechanism is also
discussed in some detail.Comment: 27 pages, 10 figure
New Skyrme energy density functional for a better description of the Gamow-Teller Resonance
We present a new Skyrme energy density functional (EDF) named SAMi [Phys.
Rev. C 86 031306(R)]. This interaction has been accurately calibrated to
reproduce properties of doubly-magic nuclei and infinite nuclear matter. The
novelties introduced in the model and fitting protocol of SAMi are crucial for
a better description of the Gamow-Teller Resonance (GTR). Those are, on one
side, the two-component spin-orbit potential needed for describing different
proton high-angular momentum spin-orbit splitings and, on the other side, the
careful description of the empirical hierarchy and positive values found in
previous analysis of the spin (G_0) and spin-isospin (G_0^') Landau-Migdal
parameters: 0 < G_0 < G_0^', a feature that many of available Skyrme forces
fail to reproduce. When employed within the self-consistent Hartree-Fock plus
Random Phase Approximation, SAMi produces results on ground and excited state
nuclear properties that are in good agreement with experimental findings. This
is true not only for the GTR, but also for the Spin Dipole Resonance (SDR) and
the Isobaric Analog Resonance (IAR) as well as for the non charge-exchange
Isoscalar Giant Monopole (ISGMR) and Isovector Giant Dipole (IVGDR) and
Quadrupole Resonances (IVGQR).Comment: Proceedings of the Nuclear Physics Workshop "Marie & Pierre Curie"
Kazimierz 2012. To appear in Physica Script
Isovector spin-singlet (T=1, S=0) and isoscalar spin-triplet (T=0, S=1) pairing interactions and spin-isospin response
We review several experimental and theoretical advances that emphasise common
aspects of the study of T=1 and T=0 pairing correlations in nuclei. We first
discuss several empirical evidences of the special role played by the T=1
pairing interaction. In particular, we show the peculiar features of the
nuclear pairing interaction in the low density regime, and possible outcomes
such as the BCS-BEC crossover in nuclear matter and, in an analogous way, in
loosely bound nuclei. We then move to the competition between T=1 and T=0
pairing correlations. The effect of such competition on the low-lying spectra
is studied in N=Z odd-odd nuclei by using a three-body model; it is shown that
the inversion of the 0+ and 1+ states near the ground state, and the strong
magnetic dipole transitions between them, can be considered as a clear
manifestation of strong T=0 pairing correlations in these nuclei. The effect of
T=0 pairing correlations is also quite evident if one studies charge-changing
transitions. The Gamow-Teller (GT) states in N=Z+2 nuclei are studied here by
using self-consistent HFB+QRPA calculations in which the T=0 pairing
interaction is taken into account. Strong GT states are found, near the ground
state of daughter nuclei; these are compared with available experimental data
from charge-exchange reactions, and such comparison can pinpoint the value of
the strength of the T=0 interaction. Pair transfer reactions are eventually
discussed: while two-neutron transfer has been long proposed as a tool to
measure the T=1 superfluidity in the nuclear ground states, the study of
deuteron transfer is still in its infancy, despite its potential interest in
revealing effects coming from both T=1 and T=0 interactions.Comment: Paper submitted to Physica Scripta for inclusion in the Focus Issue
entitled "Focus Issue on Nuclear Structure: Celebrating the 75 Nobel Prize"
(by A. Bohr and B.R. Mottelson). arXiv admin note: text overlap with
arXiv:nucl-th/0512021 by other author
The nuclear symmetry energy and other isovector observables from the point of view of nuclear structure
In this contribution, we review some works related with the extraction of the
symmetry energy parameters from isovector nuclear excitations, like the giant
resonances. Then, we move to the general issue of how to assess whether
correlations between a parameter of the nuclear equation of state and a nuclear
observable are robust or not. To this aim, we introduce the covariance analysis
and we discuss some counter-intuitive, yet enlightening, results from it.Comment: To be published in the proceedings of the 2014 Zakopane Conference on
Nuclear Physics (Acta Physica Polonica B
Dipole states in stable and unstable nuclei
A nuclear structure model based on linear response theory (i.e., Random Phase
Approximation) and which includes pairing correlations and anharmonicities
(coupling with collective vibrations), has been implemented in such a way that
it can be applied on the same footing to magic as well as open-shell nuclei. As
applications, we have chosen to study the dipole excitations both in
well-known, stable isotopes like Pb and Sn as well as in the
neutron-rich, unstable Sn nucleus, by addressing in the latter case the
question about the nature of the low-lying strength. Our results suggest that
the model is reliable and predicts in all cases low-lying strength of non
collective nature.Comment: 16 pages, 6 figures; submitted for publicatio
Exotic modes of excitation in atomic nuclei far from stability
We review recent studies of the evolution of collective excitations in atomic
nuclei far from the valley of -stability. Collective degrees of freedom
govern essential aspects of nuclear structure, and for several decades the
study of collective modes such as rotations and vibrations has played a vital
role in our understanding of complex properties of nuclei. The multipole
response of unstable nuclei and the possible occurrence of new exotic modes of
excitation in weakly-bound nuclear systems, present a rapidly growing field of
research, but only few experimental studies of these phenomena have been
reported so far. Valuable data on the evolution of the low-energy dipole
response in unstable neutron-rich nuclei have been gathered in recent
experiments, but the available information is not sufficient to determine the
nature of observed excitations. Even in stable nuclei various modes of giant
collective oscillations had been predicted by theory years before they were
observed, and for that reason it is very important to perform detailed
theoretical studies of the evolution of collective modes of excitation in
nuclei far from stability. We therefore discuss the modern theoretical tools
that have been developed in recent years for the description of collective
excitations in weakly-bound nuclei. The review focuses on the applications of
these models to studies of the evolution of low-energy dipole modes from stable
nuclei to systems near the particle emission threshold, to analyses of various
isoscalar modes, those for which data are already available, as well as those
that could be observed in future experiments, to a description of
charge-exchange modes and their evolution in neutron-rich nuclei, and to
studies of the role of exotic low-energy modes in astrophysical processes.Comment: 123 pages, 59 figures, submitted to Reports on Progress in Physic
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