114 research outputs found
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
Toroidal dipole resonances in the relativistic random phase approximation
The isoscalar toroidal dipole strength distributions in spherical nuclei are
calculated in the framework of a fully consistent relativistic random phase
approximation. It is suggested that the recently observed "low-lying component
of the isoscalar dipole mode" might in fact correspond to the toroidal giant
dipole resonance. Although predicted by several theoretical models, the
existence of toroidal resonances has not yet been confirmed in experiment. The
strong mixing between the toroidal resonance and the dipole compression mode
might help to explain the large discrepancy between theory and experiment on
the position of isoscalar giant dipole resonances.Comment: 10 pages, 3 figures; Phys.Rev.C, in prin
Relativistic description of exotic collective excitation phenomena in atomic nuclei
The low-lying dipole and quadrupole states in neutron rich nuclei, are
studied within the fully self-consistent relativistic quasiparticle
random-phase approximation (RQRPA), formulated in the canonical basis of the
Relativistic Hartree-Bogoliubov model (RHB), which is extended to include the
density dependent interactions. In heavier nuclei, the low-lying E1 excited
state is identified as a pygmy dipole resonance (PDR), i.e. as a collective
mode of excess neutrons oscillating against a proton-neutron core. Isotopic
dependence of the PDR is characterized by a crossing between the PDR and
one-neutron separation energies. Already at moderate proton-neutron asymmetry
the PDR peak is calculated above the neutron emission threshold, indicating
important implications for the observation of the PDR in (gamma,gamma')
scattering, and on the theoretical predictions of the radiative neutron capture
rates in neutron-rich nuclei. In addition, a novel method is suggested for
determining the neutron skin of nuclei, based on measurement of excitation
energies of the Gamow-Teller resonance relative to the isobaric analog state.Comment: 8 pages, 3 figures, invited talk at the international workshop
"Blueprints for the nucleus: From First Principles to Collective Motion", May
17-22. 2004, Istanbul, Turkey; to appear in Int. J. Mod. Phys.
Microscopic description of nuclear quantum phase transitions
The relativistic mean-field framework, extended to include correlations
related to restoration of broken symmetries and to fluctuations of the
quadrupole deformation, is applied to a study of shape transitions in Nd
isotopes. It is demonstrated that the microscopic self-consistent approach,
based on global effective interactions, can describe not only general features
of transitions between spherical and deformed nuclei, but also the singular
properties of excitation spectra and transition rates at the critical point of
quantum shape phase transition.Comment: 10 pages, 4 figures, accepted for publication in Physical Review
Letter
Microscopic description of octupole shape-phase transitions in light actinides and rare-earth nuclei
A systematic analysis of low-lying quadrupole and octupole collective states
is presented, based on the microscopic energy density functional framework. By
mapping the deformation constrained self-consistent axially symmetric
mean-field energy surfaces onto the equivalent Hamiltonian of the
interacting boson model (IBM), that is, onto the energy expectation value in
the boson condensate state, the Hamiltonian parameters are determined. The
study is based on the global relativistic energy density functional DD-PC1. The
resulting IBM Hamiltonian is used to calculate excitation spectra and
transition rates for the positive- and negative-parity collective states in
four isotopic chains characteristic for two regions of octupole deformation and
collectivity: Th, Ra, Sm and Ba. Consistent with the empirical trend, the
microscopic calculation based on the systematics of -
energy maps, the resulting low-lying negative-parity bands and transition rates
show evidence of a shape transition between stable octupole deformation and
octupole vibrations characteristic for -soft potentials.Comment: 18 pages, 18 figures, 1 tabl
Non-empirical nuclear energy functionals, pairing gaps and odd-even mass differences
First, we briefly outline some aspects of the starting project to design
non-empirical energy functionals based on low-momentum vacuum interactions and
many-body perturbation theory. Second, we present results obtained within an
approximation of such a scheme where the pairing part of the energy density
functional is constructed at first order in the nuclear plus Coulomb two-body
interaction. We discuss in detail the physics of the odd-even mass staggering
and the necessity to compute actual odd-even mass differences to analyze it
meaningfully.Comment: 8 pages, 1 figure, proceedings of the International Conference on
Nuclear Structure and Dynamics, Dubrovnik, Croatia, May 4 - 8, 200
Finite- to zero-range relativistic mean-field interactions
We study the relation between the finite-range (meson-exchange) and
zero-range (point-coupling) representations of effective nuclear interactions
in the relativistic mean-field framework. Starting from the phenomenological
interaction DD-ME2 with density-dependent meson-nucleon couplings, we construct
a family of point-coupling effective interactions for different values of the
strength parameter of the isoscalar-scalar derivative term. In the
meson-exchange picture this corresponds to different values of the
-meson mass. The parameters of the isoscalar-scalar and
isovector-vector channels of the point-coupling interactions are adjusted to
nuclear matter and ground-state properties of finite nuclei. By comparing
results for infinite and semi-infinite nuclear matter, ground-state masses,
charge radii, and collective excitations, we discuss constraints on the
parameters of phenomenological point-coupling relativistic effective
interaction.Comment: 25 pages, 5 figures, accepted for publication in Physical Review
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