3,213 research outputs found
Eigenstates of the time-dependent density-matrix theory
An extended time-dependent Hartree-Fock theory, known as the time-dependent
density-matrix theory (TDDM), is solved as a time-independent eigenvalue
problem for low-lying states in O to understand the foundation of
the rather successful time-dependent approach. It is found that the calculated
strength distribution of the states has physically reasonable behavior
and that the strength function is practically positive definite though the
non-hermitian hamiltonian matrix obtained from TDDM does not guarantee it. A
relation to an extended RPA theory with hermiticity is also investigated. It is
found that the density-matrix formalism is a good approximation to the
hermitian extended RPA theory.Comment: 8 pages, 1 figur
Surface properties of nuclear pairing with the Gogny force in a simplified model
Surface properties of neutron-neutron (T=1) pairing in semi-infinite nuclear
matter in a hard wall potential are investigated in BCS approximation using the
Gogny force. Surface enhancement of the gap function, pairing tensor and
correlation energy density is put into evidence.Comment: 16 pages; 4 figures ; submitted to Phys. Lett.
Thomas-Fermi approximation to static vortex states in superfluid trapped atomic gases
We revise the Thomas-Fermi approximation for describing vortex states in Bose
condensates of magnetically trapped atoms. Our approach is based on considering
the hbar -> 0 limit rather than the N -> infinity limit as Thomas-Fermi
approximation in close analogy with the Fermi systems. Even for relatively
small numbers of trapped particles we find good agreement between
Gross-Pitaevskii and Thomas-Fermi calculations for the different contributions
to the total energy of the atoms in the condensate. We also discuss the
application of our approach to the description of vortex states in superfluid
fermionic systems in the Ginzburg-Landau regime.Comment: 11 pages, 6 figures, revtex4, substantially revised versio
Semi-Classical Description of the Average Pairing Properties in Nuclei
We present a new semi-classical theory for describing pairing in finite Fermi
systems. It is based in taking the , i.e. Thomas-Fermi, limit of
the gap equation written in the basis of the mean field (weak coupling). In
addition to the position dependence of the Fermi momentum, the size dependence
of the matrix elements of the pairing force is also taken into account in this
theory. An example typical for the nuclear situation shows the improvement of
this new approach over the standard Local Density Approximation. We also show
that if in this approach some shell fluctuations are introduced in the level
density, the arch structure displayed by the quantal gaps along isotopic chains
is almost recovered. We also point out that in heavy drip line nuclei pairing
is strongly reduced
Octupole deformation properties of the Barcelona-Catania-Paris energy density functionals
We discuss the octupole deformation properties of the recently proposed
Barcelona-Catania-Paris (BCP) energy density functionals for two sets of
isotopes, those of radium and barium, where it is believed that octupole
deformation plays a role in the description of the ground state. The analysis
is carried out in the mean field framework (Hartree- Fock- Bogoliubov
approximation) by using the axially symmetric octupole moment as a constraint.
The main ingredients entering the octupole collective Hamiltonian are evaluated
and the lowest lying octupole eigenstates are obtained. In this way we restore,
in an approximate way, the parity symmetry spontaneously broken by the mean
field and also incorporate octupole fluctuations around the ground state
solution. For each isotope the energy of the lowest lying state and the
and transition probabilities have been computed and compared to
both the experimental data and the results obtained in the same framework with
the Gogny D1S interaction, which are used here as a well established benchmark.
Finally, the octupolarity of the configurations involved in the way down to
fission of Pu, which is strongly connected to the asymmetric fragment
mass distribution, is studied. We confirm with this thorough study the
suitability of the BCP functionals to describe octupole related phenomena.Comment: 13 pages, 13 figure
Accurate nuclear masses from a three parameter Kohn-Sham DFT approach (BCPM)
Given the promising features of the recently proposed Barcelona-Catania-Paris
(BCP) functional \cite{Baldo.08}, it is the purpose of this paper to still
improve on it. It is, for instance, shown that the number of open parameters
can be reduced from 4-5 to 2-3, i.e. by practically a factor of two. One
parameter is tightly fixed by a fine-tuning of the bulk, a second by the
surface energy. The third is the strength of the spin-orbit potential on which
the final result does not depend within the scatter of the values used in
Skyrme and Gogny like functionals. An energy rms value of 1.58 MeV is obtained
from a fit of these three parameters to the 579 measured masses reported in the
Audi and Waspra 2003 compilation. This rms value compares favorably with the
one obtained using other successful mean field theories. Charge radii are also
well reproduced when compared with experiment. The energies of some excited
states, mostly the isoscalar giant monopole resonances, are studied within this
model as well.Comment: 23 pages, 12 figure
Chaoticity and Dissipation of Nuclear Collective Motion in a Classical Model
We analyze the behavior of a gas of classical particles moving in a
two-dimensional "nuclear" billiard whose multipole-deformed walls undergo
periodic shape oscillations. We demonstrate that a single particle Hamiltonian
containing coupling terms between the particles' motion and the collective
coordinate induces a chaotic dynamics for any multipolarity, independently on
the geometry of the billiard. The absence of coupling terms allows us to
recover qualitatively the "wall formula" predictions. We also discuss the
dissipative behavior of the wall motion and its relation with the
order-to-chaos transition in the dynamics of the microscopic degrees of
freedom.Comment: LateX, 11 pages, 7 figures available on request, to appear in the
Proceedings of XXXIV Winter Meeting on Nuclear Physics, Bormio 22-27 January,
199
Deuteron formation in nuclear matter
We investigate deuteron formation in nuclear matter at finite temperatures
within a systematic quantum statistical approach. We consider formation through
three-body collisions relevant already at rather moderate densities because of
the strong correlations. The three-body in-medium reaction rates driven by the
break-up cross section are calculated using exact three-body equations
(Alt-Grassberger-Sandhas type) that have been suitably modified to consistently
include the energy shift and the Pauli blocking. Important quantities are the
lifetime of deuteron fluctuations and the chemical relaxation time. We find
that the respective times differ substantially while using in-medium or
isolated cross sections. We expect implications for the description of heavy
ion collisions in particular for the formation of light charged particles at
low to intermediate energies.Comment: 19 pages, 5 figure
Size-shrinking of deuterons in very dilute superfluid nuclear matter
It is shown within the strong-coupling BCS approach that, starting from the
zero-density limit of superfluid nuclear matter, with increasing density
deuterons first shrink before they start expanding.Comment: 2 pages, Latex, 1 figure included, submitted to Phys. Rev.
Pairing correlations of cold fermionic gases at overflow from a narrow to a wide harmonic trap
Within the context of Hartree-Fock-Bogoliubov theory, we study the behavior
of superfluid Fermi systems when they pass from a small to a large container.
Such systems can be now realized thanks to recent progress in experimental
techniques. It will allow to better understand pairing properties at overflow
and in general in rapidly varying external potentials
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