40,243 research outputs found
New parametrization for the nuclear covariant energy density functional with point-coupling interaction
A new parametrization PC-PK1 for the nuclear covariant energy density
functional with nonlinear point-coupling interaction is proposed by fitting to
observables for 60 selected spherical nuclei, including the binding energies,
charge radii and empirical pairing gaps. The success of PC-PK1 is illustrated
in its description for infinite nuclear matter and finite nuclei including the
ground-state and low-lying excited states. Particularly, PC-PK1 improves the
description for isospin dependence of binding energy along either the isotopic
or the isotonic chains, which makes it more reliable for application in exotic
nuclei. The predictive power of PC-PK1 is also illustrated for the nuclear
low-lying excitation states in a five-dimensional collective Hamiltonian in
which the parameters are determined by constrained calculations for triaxial
shapes.Comment: 32 pages, 12 figures, 4 tables, accepted by Phys. Rev.
Relativistic description of nuclear matrix elements in neutrinoless double- decay
Neutrinoless double- () decay is related to many
fundamental concepts in nuclear and particle physics beyond the standard model.
Currently there are many experiments searching for this weak process. An
accurate knowledge of the nuclear matrix element for the decay
is essential for determining the effective neutrino mass once this process is
eventually measured. We report the first full relativistic description of the
decay matrix element based on a state-of-the-art nuclear
structure model. We adopt the full relativistic transition operators which are
derived with the charge-changing nucleonic currents composed of the vector
coupling, axial-vector coupling, pseudoscalar coupling, and weak-magnetism
coupling terms. The wave functions for the initial and final nuclei are
determined by the multireference covariant density functional theory (MR-CDFT)
based on the point-coupling functional PC-PK1. The low-energy spectra and
electric quadrupole transitions in Nd and its daughter nucleus
Sm are well reproduced by the MR-CDFT calculations. The
decay matrix elements for both the
and decays of Nd are evaluated. The effects
of particle number projection, static and dynamic deformations, and the full
relativistic structure of the transition operators on the matrix elements are
studied in detail. The resulting decay matrix element for the
transition is , which gives the most optimistic
prediction for the next generation of experiments searching for the
decay in Nd.Comment: 17 pages, 9 figures; table adde
Does a proton "bubble" structure exist in the low-lying states of 34Si?
The possible existence of a "bubble" structure in the proton density of
Si has recently attracted a lot of research interest. To examine the
existence of the "bubble" structure in low-lying states, we establish a
relativistic version of configuration mixing of both particle number and
angular momentum projected quadrupole deformed mean-field states and apply this
state-of-the-art beyond relativistic mean-field method to study the density
distribution of the low-lying states in Si. An excellent agreement with
the data of low-spin spectrum and electric multipole transition strengths is
achieved without introducing any parameters. We find that the central
depression in the proton density is quenched by dynamic quadrupole shape
fluctuation, but not as significantly as what has been found in a beyond
non-relativistic mean-field study. Our results suggest that the existence of
proton "bubble" structure in the low-lying excited and states
is very unlikely.Comment: 6 pages, 8 figures and 1 table, accepted for publication in Physics
Letters
Anatomy of molecular structures in Ne
We present a beyond mean-field study of clusters and molecular structures in
low-spin states of Ne with a multireference relativistic energy density
functional, where the dynamical correlation effects of symmetry restoration and
quadrupole-octupole shapes fluctuation are taken into account with projections
on parity, particle number and angular momentum in the framework of the
generator coordinate method. Both the energy spectrum and the electric
multipole transition strengths for low-lying parity-doublet bands are better
reproduced after taking into account the dynamical octupole vibration effect.
Consistent with the finding in previous studies, a rotation-induced dissolution
of the O molecular structure in Ne is predicted.Comment: 6 pages with 6 figures, version to be published in Phys. Lett.
Configuration mixing of angular-momentum projected triaxial relativistic mean-field wave functions
The framework of relativistic energy density functionals is extended to
include correlations related to the restoration of broken symmetries and to
fluctuations of collective variables. The generator coordinate method is used
to perform configuration mixing of angular-momentum projected wave functions,
generated by constrained self-consistent relativistic mean-field calculations
for triaxial shapes. The effects of triaxial deformation and of -mixing is
illustrated in a study of spectroscopic properties of low-spin states in
Mg.Comment: 15 pages, 11 figures, 4 tables, accepted for publication in Phys.
Rev.
Effect of pairing correlations on nuclear low-energy structure: BCS and general Bogoliubov transformation
Low-lying nuclear states of Sm isotopes are studied in the framework of a
collective Hamiltonian based on covariant energy density functional theory.
Pairing correlation are treated by both BCS and Bogoliubov methods. It is found
that the pairing correlations deduced from relativistic Hartree-Bogoliubov
(RHB) calculations are generally stronger than those by relativistic mean-field
plus BCS (RMF+BCS) with same pairing force. By simply renormalizing the pairing
strength, the diagonal part of the pairing field is changed in such a way that
the essential effects of the off-diagonal parts of the pairing field neglected
in the RMF+BCS calculations can be recovered, and consequently the low-energy
structure is in a good agreement with the predictions of the RHB model.Comment: 5 figures, 5 page
Rapid structural change in low-lying states of neutron-rich Sr and Zr isotopes
The rapid structural change in low-lying collective excitation states of
neutron-rich Sr and Zr isotopes is tudied by solving a five-dimensional
collective Hamiltonian with parameters determined by both relativistic
mean-field and non-relativistic Skyrme-Hartree-Fock calculations using the
PC-PK1 and SLy4 forces respectively. Pair correlations are treated in BCS
method with either a separable pairing force or a density-dependent zero-range
force. The isotope shifts, excitation energies, electric monopole and
quadrupole transition strengths are calculated and compared with corresponding
experimental data. The calculated results with both the PC-PK1 and SLy4 forces
exhibit a picture of spherical-oblate-prolate shape transition in neutron-rich
Sr and Zr isotopes. Compared with the experimental data, the PC-PK1 (or SLy4)
force predicts a more moderate (or dramatic) change in most of the collective
properties around N=60. The underlying microscopic mechanism responsible for
the rapid transition is discussed.Comment: 10 pages (twocolumn), 10 figure
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