22,955 research outputs found
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
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.
Covariant description of shape evolution and shape coexistence in neutron-rich nuclei at N\approx60
The shape evolution and shape coexistence phenomena in neutron-rich nuclei at
, including Kr, Sr, Zr, and Mo isotopes, are studied in the
covariant density functional theory (DFT) with the new parameter set PC-PK1.
Pairing correlations are treated using the BCS approximation with a separable
pairing force. Sharp rising in the charge radii of Sr and Zr isotopes at N=60
is observed and shown to be related to the rapid changing in nuclear shapes.
The shape evolution is moderate in neighboring Kr and Mo isotopes. Similar as
the results of previous Hartree-Fock-Bogogliubov (HFB) calculations with the
Gogny force, triaxiality is observed in Mo isotopes and shown to be essential
to reproduce quantitatively the corresponding charge radii. In addition, the
coexistence of prolate and oblate shapes is found in both Sr and
Zr. The observed oblate and prolate minima are related to the low
single-particle energy level density around the Fermi surfaces of neutron and
proton respectively. Furthermore, the 5-dimensional (5D) collective Hamiltonian
determined by the calculations of the PC-PK1 energy functional is solved for
Sr and Zr. The resultant excitation energy of state and
E0 transition strength are in rather good
agreement with the data. It is found that the lower barrier height separating
the two competing minima along the deformation in Zr gives
rise to the larger than that in Sr.Comment: 1 table, 11 figures, 23 page
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.
Neutrino emission from a GRB afterglow shock during an inner supernova shock breakout
The observations of a nearby low-luminosity gamma-ray burst (GRB) 060218
associated with supernova SN 2006aj may imply an interesting astronomical
picture where a supernova shock breakout locates behind a relativistic GRB jet.
Based on this picture, we study neutrino emission for early afterglows of GRB
060218-like GRBs, where neutrinos are expected to be produced from photopion
interactions in a GRB blast wave that propagates into a dense wind.
Relativistic protons for the interactions are accelerated by an external shock,
while target photons are basically provided by the incoming thermal emission
from the shock breakout and its inverse-Compton scattered component. Because of
a high estimated event rate of low-luminosity GRBs, we would have more
opportunities to detect afterglow neutrinos from a single nearby GRB event of
this type by IceCube. Such a possible detection could provide evidence for the
picture described above.Comment: 6 pages, 2 figures, accepted for publication in MNRA
An efficient method for computing the Thouless-Valatin inertia parameters
Starting from the adiabatic time-dependent Hartree-Fock approximation
(ATDHF), we propose an efficient method to calculate the Thouless-Valatin
moments of inertia for the nuclear system. The method is based on the rapid
convergence of the expansion of the inertia matrix. The accuracy of the
proposed method is verified in the rotational case by comparing the results
with the exact Thouless-Valatin moments of inertia calculated using the
self-consistent cranking model. The proposed method is computationally much
more efficient than the full ATDHF calculation, yet it retains a high accuracy
of the order of 1%.Comment: 16 pages, 3 figure
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
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
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