P. Schuck

Dilute Multi Alpha Cluster States in Nuclei

Dilute multicluster condensed states with spherical and axially deformed shapes are studied with the Gross-Pitaevskii equation and Hill-Wheeler equation, where thecluster is treated as a structureless boson. Applications to self-conjugate 4N nuclei show that the dilute Nstates of 12 C to 40 Ca with J � = 0 + appear in the energy region from threshold up to about 20 MeV, and the critical number ofbosons that the dilute Nsystem can sustain as a self-bound nucleus is estimated roughly to be Ncr ∼ 10. We discuss the charac- teristics of the dilute Nstates with emphasis on the N dependence of their energies and rms radii.

Single α-particle orbits and Bose-Einstein condensation in 12C

Abstract.Bosonic properties of α particles such as single-α orbits and occupation numbers in Jπ = 0+, 2+, 1- and 3- states of 12C around the 3α threshold are investigated with the semi-microscopic 3α cluster model. As in other studies, we found that the 0+2 (2+2) state has dilute-3α-condensate-like structure in which the α particle is occupied in the single S (D) orbit with about 70% (80%) probability. The radial behaviors of the single-α orbits as well as the occupation numbers are discussed in detail in comparison with those for the 0+1 and 2+1 states together with the 1-1 and 3-1 states.

Effective density-dependent pairing forces in the T=1 and T=0 channels

This work was supported by DGICYT-IN2P3 agreement and by DGICYT (Spain) under Contract No. PB95/0123.

Relativistic mean field interaction with density dependent meson-nucleon vertices based on microscopical calculations

Although ab initio calculations of relativistic Brueckner theory lead to large scalar isovector fields in nuclear matter, at present, successful versions of covariant density functional theory neglect the interactions in this channel. A new high-precision density functional DD-MEδ is presented which includes four mesons, σ , ω, δ, and ρ, with density-dependent meson-nucleon couplings. It is based to a large extent on microscopic ab initio calculations in nuclear matter. Only four of its parameters are determined by adjusting to binding energies and charge radii of finite nuclei. The other parameters, in particular the density dependence of the meson-nucleon vertices, are adjusted to nonrelativistic and relativistic Brueckner calculations of symmetric and asymmetric nuclear matter. The isovector effective mass m ∗ − m ∗ derived from relativistic Brueckner theory is used to determine the coupling strength of the δ meson and its density dependence.

Low densities in nuclear and neutron matters and in the nuclear surface

Abstract Nuclear and neutron matters are investigated in the low density region, well below the nuclear saturation density. Microscopic calculations, based on the Bethe–Brueckner approach with a few realistic nucleon–nucleon potentials, are compared with the predictions of a set of phenomenological effective interactions, mostly employed in nuclear structure studies. An energy functional is constructed on the basis of the microscopic bulk EoS and applied to a selection of nuclei throughout the mass table. The results provide a microscopic basis for a link between nuclear surface behaviour and neutron EoS previously observed with phenomenological effective forces. Possible effects of pairing on asymmetric nuclear matter are also analyzed in detail. The results are expected to illuminate the physical mechanisms which determine the behaviour of the surface density tail in exotic nuclei.

Generalized Brückner-Hartree-Fock theory and self-consistent RPA

Abstract Self-consistent RPA (SCRPA) theory is developed in the particle-particle (pp) channel. It is pointed out that in this way vertex and self-energy corrections are taken into account on an equal footing whereas in Bruckner-Hartree-Fock (BHF) this is not the case. We discuss in detail the interconnection between both theories and apply them to a model case. Excellent agreement with the exact solution is found for SCRPA where as BHF gives somewhat poorer results. In an appendix it is demonstrated how SCRPA connects to a variational principle and how, for the particle-hole case, sum rules and conservation laws are fulfilled.

Fermion condensation and non Fermi liquid behavior in a model with long range forces

The phenomenon of the so called Fermion condensation, a phase transition analogous to Bose condensation but for Fermions, postulated in the past to occur in systems with strong momentum dependent forces, is reanalyzed in a model with infinite range interactions. The strongly non Fermi Liquid behavior of this system is demonstrated analytically at T = 0 and at T ≠ 0 in the superconducting and normal phases. The validity of the quasiparticle picture is investigated and seen to hold true for temperatures less than the characteristic temperature Tf of the Fermion condensation.

S-Wave ππ Correlations in Dense Nuclear Matter

The s-wave correlated �-� strength distribution in cold nuclear matter is investigated. The in-medium single pions are renormalized by means of the usual p-wave couplings to nucleons and �’s. Two groups of models for the �-� interaction are studied. The first one uses phenomenological models which reproduce the phase shifts but do not respect the soft-pion theorems. With increasing density a strong accumulation of strength in the subhreshold region is observed. Slightly above saturation density there even occurs an instability with respect to s-wave �-�pair condensation. These effects are strongly moderated or disappear altogether if constraints from chiral symmetry are built into the �-� interaction.

Description of 8Be as Deformed Gas-Like Two-Alpha-Particle States

In order to study non-zero spin excitations of the recently proposed α-cluster condensation in the self-conjugate 4n nuclei, spatial deformation is introduced into the model wave function of the α-cluster condensate. The rotational band states of 8 Be are investigated as a first step of a test case for the study of the deformation of the α-cluster condensate. Calculations reproduce well the binding energy of the 0 + ground state and also the excitation energy of the 2 + state. Our 0 + wave function is found to be almost exactly equal to the 0 + wave function obtained by the generator coordinate method using Brinks 2α wave function. The study shows that both the 0 + ground and 2 + excited states can be considered as having a gas-like (i.e. weakly bound) 2α-cluster structure. As for the 0 + ground state, the change of the wave function, due to the introduction of the deformation, is found to be very small.

Correlation effects on the level density of a hot nucleus

Abstract The previously introduced model for correlation effects on the level density parameter, a, is generalized to finite temperatures. It is found that the increase of a due to the correlations at zero temperature vanishes within a certain range around T ≈ 4 MeV, in agreement with recent experimental studies.