4,471 research outputs found
Comment on "Pygmy dipole response of proton-rich argon nuclei in random-phase approximation and no-core shell model"
In a recent article by C. Barbieri, E. Caurier, K. Langanke, and G.
Mart\'inez-Pinedo \cite{Bar.08}, low-energy dipole excitations were studied in
proton-rich Ar with random-phase approximation (RPA) and no-core
shell model (NCSM) using correlated realistic nucleon-nucleon interactions
obtained by the unitary correlation operator method (UCOM) \cite{Fel.98}. The
main objective of this Comment is to argue that the article \cite{Bar.08}
contains an inconsistency with respect to previous study of excitations in the
same UCOM-RPA framework using identical correlated Argonne V18 interaction
\cite{Paa.06}, it does not provide any evidence that the low-lying state
declared as pygmy dipole resonance in Ar indeed has the resonance-like
structure, and that prior to studying exotic modes of excitation away from the
valley of stability one should ensure that the model provides reliable
description of available experimental data on nuclear ground state properties
and excitations in nuclei. Although the authors aimed at testing the UCOM based
theory at the proton drip line, available experimental data that are used as
standard initial tests of theory frameworks at the proton drip line have not
been considered in the UCOM case (e.g., binding energies, one-proton separation
energies, two-proton separation energies).Comment: 2 pages, revised version, accepted for publication in Phys. Rev.
Resolving neutrino mass hierarchy from supernova (anti)neutrino-nucleus reactions
We introduce a hybrid method to determine neutrino mass hierarchy by
simultaneous measurements of detector responses induced by antineutrino and
neutrino fluxes from accretion and cooling phase of type II supernova. The
(anti)neutrino-nucleus cross sections for C, O, Fe and
Pb are calculated in the framework of relativistic nuclear energy
density functional and weak Hamiltonian, while the cross sections for inelastic
scattering on free protons, , are obtained using
heavy-baryon chiral perturbation theory. The simulations of (anti)neutrino
fluxes emitted from a protoneutron star in a core-collapse supernova include
collective and Mickheev-Smirnov-Wolfenstein effects inside star. The emission
rates of elementary decay modes of daughter nuclei are calculated for normal
and inverted neutrino mass hierarchy. It is shown that simultaneous use of
(anti)neutrino detectors with different target material and time dependence of
the signal allow to determine the neutrino mass hierarchy from the ratios of
induced particle emissions. The hybrid method favors
detectors with heavier target nuclei (Pb) for the neutrino sector,
while for antineutrinos the use of free protons and light nuclei
( or ) represent appropriate choice.Comment: 4 pages, 2 figures, 1 tabl
Magnetic dipole excitation and its sum rule in nuclei with two valence nucleons
Background: Magnetic dipole (M1) excitation is the leading mode of nuclear
excitation by the magnetic field, which couples unnatural-parity states. Since
the M1 excitation occurs mainly for open-shell nuclei, the nuclear pairing
effect is expected to play a role. As expected from the form of operator, this
mode may provide the information on the spin-related properties, including the
spin component of dineutron and diproton correlations. In general, the sum rule
for M1 transition strength has not been derived yet. Purpose: To investigate
the M1 excitation of the systems with two valence nucleons above the
closed-shell core, with pairing correlation included, and to establish the M1
sum rule that could be used to validate theoretical and experimental
approaches. Possibility to utilize the M1 excitation as a tool to investigate
the pairing correlation in medium is also discussed. Method: Three-body model,
which consists of a rigid spherical core and two valence nucleons, is employed.
Interactions for its two-body subsystems are phenomenologically determined in
order to reproduce the two-body and three-body energies. We also derive the M1
sum rule within this three-body picture. Conclusion: The introduced M1 sum rule
can be utilized as a benchmark for model calculations of M1 transitions in the
systems with two valence nucleons. The total sum of the M1 transition strength
is related with the coupled spin of valence nucleons in the open shell, where
the pairing correlation is unnegligible. The three-body-model calculations for
18 O, 18 Ne, and 42 Ca nuclei demonstrate a significant effect of the pairing
correlations on the low-lying M1 transitions. Therefore, further experimental
studies of M1 transitions in those systems are on demand, in order to validate
proposed sum rule, provide a suitable probe for the nuclear pairing in medium,
as well as to optimize the pairing models.Comment: 10 pages, 3 figures, 4 tables. Revised for re-submission to Phys.
Rev.
Parry measure and the topological entropy of chaotic repellers embedded within chaotic attractors
We study the topological entropy of chaotic repellers formed by those points
in a given chaotic attractor that never visit some small forbidden hole-region
in the phase space. The hole is a set of points in the phase space that have a
sequence as the first letters in
their itineraries. We point out that the difference between the topological
entropies of the attractor and the embedded repeller is for most choices of
approximately equal to the Parry measure corresponding to ,
. When the hole encompasses a point of a short periodic orbit,
the entropy difference is significantly smaller than . This
discrepancy is described by the formula which relates the length of the short
periodic orbit, the Parry measure , and the topological
entropies of the two chaotic sets.Comment: Submitted to Physica
The Proton Electric Pygmy Dipole Resonance
The evolution of the low-lying E1 strength in proton-rich nuclei is analyzed
in the framework of the self-consistent relativistic Hartree-Bogoliubov (RHB)
model and the relativistic quasiparticle random-phase approximation (RQRPA).
Model calculations are performed for a series of N=20 isotones and Z=18
isotopes. For nuclei close to the proton drip-line, the occurrence of
pronounced dipole peaks is predicted in the low-energy region below 10 MeV
excitation energy. From the analysis of the proton and neutron transition
densities and the structure of the RQRPA amplitudes, it is shown that these
states correspond to the proton pygmy dipole resonance.Comment: 7 pages, 4 figures, to be published in Phys. Rev. Let
Low-energy dipole excitations towards the proton drip-line: doubly magic 48Ni
The properties of the low-energy dipole response are investigated for the
proton-rich doubly magic nucleus Ni, in a comparative study of two
microscopic models: fully self-consistent Relativistic Random-Phase
Approximation(RRPA) based on the novel density-dependent meson-exchange
interactions, and Continuum Random-Phase Approximation(CRPA) using Skyrme-type
interactions with the continuum properly included. Both models predict the
existence of the low-energy soft mode, i.e. the proton pygmy dipole resonance
(PDR), for which the transition densities and RPA amplitudes indicate the
dynamics of loosely bound protons vibrating against the rest of the nucleons.
The CRPA analysis indicates that the escape width for the proton PDR is rather
large, as a result of the coupling to the continuum.Comment: 12 pages, 3 figures, accepted for publication in Phys. Lett.
Optimizing the relativistic energy density functional with nuclear ground state and collective excitation properties
We introduce a new relativistic energy density functional constrained by the
ground state properties of atomic nuclei along with the isoscalar giant
monopole resonance energy and dipole polarizability in Pb. A unified
framework of the relativistic Hartree-Bogoliubov model and random phase
approximation based on the relativistic density-dependent point coupling
interaction is established in order to determine the DD-PCX parameterization by
minimization. This procedure is supplemented with the co-variance
analysis in order to estimate statistical uncertainties in the model parameters
and observables. The effective interaction DD-PCX accurately describes the
nuclear ground state properties including the neutron-skin thickness, as well
as the isoscalar giant monopole resonance excitation energies and dipole
polarizabilities. The implementation of the experimental data on nuclear
excitations allows constraining the symmetry energy close to the saturation
density, and the incompressibility of nuclear matter by using genuine
observables on finite nuclei in the minimization protocol, rather than
using pseudo-observables on the nuclear matter, or by relying on the ground
state properties only, as it has been customary in the previous studies.Comment: 6 pages, 3 figures, submitted to Physical Review
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
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