582 research outputs found
Random-phase approximation based on relativistic point-coupling models
The matrix equations of the random-phase approximation (RPA) are derived for
the point-coupling Lagrangian of the relativistic mean-field (RMF) model. Fully
consistent RMF plus (quasiparticle) RPA illustrative calculations of the
isoscalar monopole, isovector dipole and isoscalar quadrupole response of
spherical medium-heavy and heavy nuclei, test the phenomenological effective
interactions of the point-coupling RMF model. A comparison with experiment
shows that the best point-coupling effective interactions accurately reproduce
not only ground-state properties, but also data on excitation energies of giant
resonances.Comment: 24 pages, 4 figures, accepted for publication in Physical Review
Relativistic mean-field description of the dynamics of giant resonances
The relativistic mean-field theory provides a framework in which the nuclear
many-body problem is described as a self-consistent system of nucleons and
mesons. In the mean-field approximation, the self-consistent time evolution of
the nuclear system describes the dynamics of collective motion: nuclear
compressibility from monopole resonances, regular and chaotic dynamics of
isoscalar and isovector collective vibrations.Comment: LaTeX, 10 pages, 5 figures, Invited Talk, Topical Conference on Giant
resonances, Varenna, May 1998, to be published in Nucl. Phys.
Nonlinear dynamics of giant resonances in atomic nuclei
The dynamics of monopole giant resonances in nuclei is analyzed in the
time-dependent relativistic mean-field model. The phase spaces of isoscalar and
isovector collective oscillations are reconstructed from the time-series of
dynamical variables that characterize the proton and neutron density
distributions. The analysis of the resulting recurrence plots and correlation
dimensions indicate regular motion for the isoscalar mode, and chaotic dynamics
for the isovector oscillations. Information-theoretic functionals identify and
quantify the nonlinear dynamics of giant resonances in quantum systems that
have spatial as well as temporal structure.Comment: 24 pages, RevTeX, 15 PS figures, submitted Phys. Rev.
Nuclear pairing from chiral pion-nucleon dynamics
We use a recently improved version of the chiral nucleon-nucleon potential at
next-to-next-to-leading order to calculate the pairing gap in
isospin-symmetric nuclear matter. The pairing potential consists of the
long-range one- and two-pion exchange terms and two short-distance NN-contact
couplings. We find that the inclusion of the two-pion exchange at
next-to-next-to-leading order reduces substantially the cut-off dependence of
the pairing gap determined by solving a regularised BCS equation. Our
results are close to those obtained with the universal low-momentum
nucleon-nucleon potential or the phenomenological Gogny D1S
force.Comment: 9 pages, 3 eps figures, submitted to PR
Renormalized relativistic Hartree-Bogoliubov equations with a zero-range pairing interaction
A recently introduced scheme for the renormalization of the
Hartree-Fock-Bogoliubov equations in the case of zero-range pairing interaction
is extended to the relativistic Hartree-Bogoliubov model. A density-dependent
strength parameter of the zero-range pairing is adjusted in such a way that the
renormalization procedure reproduces the empirical pairing gap in
isospin-symmetric nuclear matter. The model is applied to the calculation of
ground-state pairing properties of finite spherical nuclei.Comment: 13 pages, 8 figures, accepted for publication in Physical Review
Beyond the relativistic Hartree mean-field approximation: energy dependent effective mass
The standard relativistic mean-field model is extended by including dynamical
effects that arise in the coupling of single-nucleon motion to collective
surface vibrations. A phenomenological scheme, based on a linear ansatz for the
energy dependence of the scalar and vector components of the nucleon
self-energy for states close to the Fermi surface, allows a simultaneous
description of binding energies, radii, deformations and single-nucleon spectra
in a self-consistent relativistic framework. The model is applied to the
spherical, doubly closed-shell nuclei 132Sn and 208Pb.Comment: 14 pages, 2 figures; replaced with revised versio
Shape-phase transitions in odd-mass -soft nuclei with mass
Quantum phase transitions between competing equilibrium shapes of nuclei with
an odd number of nucleons are explored using a microscopic framework of nuclear
energy density functionals and a particle-boson core coupling model. The boson
Hamiltonian for the even-even core nucleus, as well as the spherical
single-particle energies and occupation probabilities of unpaired nucleons, are
completely determined by a constrained self-consistent mean-field calculation
for a specific choice of the energy density functional and pairing interaction.
Only the strength parameters of the particle-core coupling have to be adjusted
to reproduce a few empirical low-energy spectroscopic properties of the
corresponding odd-mass system. The model is applied to the odd-A Ba, Xe, La and
Cs isotopes with mass , for which the corresponding even-even Ba
and Xe nuclei present a typical case of -soft nuclear potential. The
theoretical results reproduce the experimental low-energy excitation spectra
and electromagnetic properties, and confirm that a phase transition between
nearly spherical and -soft nuclear shapes occurs also in the odd-A
systems.Comment: 13 pages, 15 figures, 9 table
Signatures of shape phase transitions in odd-mass nuclei
Quantum phase transitions between competing ground-state shapes of atomic
nuclei with an odd number of protons or neutrons are investigated in a
microscopic framework based on nuclear energy density functional theory and the
particle-plus-boson-core coupling scheme. The boson-core Hamiltonian, as well
as the single-particle energies and occupation probabilities of the unpaired
nucleon, are completely determined by constrained self-consistent mean-field
calculations for a specific choice of the energy density functional and paring
interaction, and only the strength parameters of the particle-core coupling are
adjusted to reproduce selected spectroscopic properties of the odd-mass system.
We apply this method to odd-A Eu and Sm isotopes with neutron number , and explore the influence of the single unpaired fermion on the occurrence
of a shape phase transition. Collective wave functions of low-energy states are
used to compute quantities that can be related to quantum order parameters:
deformations, excitation energies, E2 transition rates and separation energies,
and their evolution with the control parameter (neutron number) is analysed.Comment: 15 pages, 13 figures; Accepted for publication in Phys. Rev.
Relativistic Random-Phase Approximation with density-dependent meson-nucleon couplings
The matrix equations of the relativistic random-phase approximation (RRPA)
are derived for an effective Lagrangian characterized by density-dependent
meson-nucleon vertex functions. The explicit density dependence of the
meson-nucleon couplings introduces rearrangement terms in the residual two-body
interaction, that are essential for a quantitative description of excited
states. Illustrative calculations of the isoscalar monopole, isovector dipole
and isoscalar quadrupole response of Pb, are performed in the fully
self-consistent RRPA framework, based on effective interactions with a
phenomenological density dependence adjusted to nuclear matter and ground-state
properties of spherical nuclei. The comparison of the RRPA results on multipole
giant resonances with experimental data constrains the parameters that
characterize the isoscalar and isovector channel of the density-dependent
effective interactions.Comment: RevTeX, 8 eps figures, submitted to Phys. Rev.
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
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