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The treatment of medium-mass and heavy nuclei represents the central part of our activities in nuclear
structure. The use of a
microscopic EFT interaction is not yet possible
in these regions of the nuclear chart and phenomenological effective
interactions are currently employed, especially within mean-field-based
models. In the last two years several goals have been achieved in the
group in the development of energy-density functionals (EDFs), in the
formulation of beyond mean-field models, and in the application of these
theories to the description of ground- and excited-state properties of
stable and exotic nucle
EDF theories constitute a wider
framework with respect to the mean-field approach and allow us to
establish connections with density functional theories developed in
condensed-matter physics and in chemistry. A considerable amount of work
has been carried out on effective interactions in the context of EDF
theories and, within the group, several different directions have been
followed such as the effect of new spin-density dependent terms, of a
surface-peaked effective mass, or in a complementary approach, a local
functional has been obtained exploiting Brueckner-Hartree-Fock
calculations. Several nuclear states lie near thresholds and breakup
into clusters. Investigations have been pursued in the last two years on
alpha clusters and condensates in excited nuclei (such as the Hoyle
state in 12C) and in low-density nuclear matter.
In a relativistic framework, density-dependent meson-nucleon couplings
have been introduced in the Hartree-Fock-Bogoliubov theory and have been
applied to study the ground-state of deformed nuclei.
The group is very active also in two other aspects of
nuclear
interactions, tensor and pairing effects. For several decades the
tensor contribution has been neglected in the most frequently used
phenomenological interactions, Skyrme and Gogny forces. Nowadays, the
impact of the tensor contribution is very much debated, especially in
connection with the structure evolution of the isotopes that are located
in the exotic regions of the nuclear chart. A new tensor term has been
very recently introduced and tested for the Gogny interaction. The
pairing interaction and the associated pairing correlations are also
extensively analyzed. Some work has been devoted to the predictions of
the size of Cooper pairs in superfluid nuclei, and to the analysis of
the effects of pairing correlations on the incompressibility and the
symmetry energy of matter. Some theoretical results obtained with
combined structure and reactions calculations have indicated that
pair-transfer reactions in very neutron-rich Sn isotopes are useful
tools to investigate the surface/volume localization of the pairing
interaction.
Similarly, our group is known for its
expertise in low-lying and giant excitations in nuclei. This subject has
been extensively analyzed with both non-relativistic and relativistic
methods. A completely self-consistent RPA calculation with the Skyrme
force have been achieved, a full calculation of the second random-phase
approximation (SRPA) for the excited states of nuclei has been
successfully applied to the description of the low-lying and giant
resonances of several nuclei. Charge-exchange excitations have been
studied in the relativistic framework. For the non-relativistic case,
giant resonances as well as Gamow-Teller and spin-dipole modes have been
analyzed with the Skyrme force. A new soft monopole mode has been
predicted as an exotic breathing mode in Ni isotopes. As far as the
low-lying dipole spectrum is concerned, pygmy resonances have been
studied with both quantum (Quasiparticle RPA and SRPA) and semiclassical
(Vlasov) models. A detailed analysis of the nature of the low-lying
states has been carried out to identify the neutron and proton
contributions and to investigate the collectivity of the states.
Institut de Physique Nucléaire Orsay - 15 rue Georges CLEMENCEAU - 91406 ORSAY (FRANCE) |
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