N. Sandulescu

Two-Particle Resonant States in a Many-Body Mean Field

A formalism to evaluate the resonant states produced by two particles moving outside a closed shell core is presented. It is found that long lived two-body states (including bound states) are mostly determined by either bound single-particle states or by narrow single-particle resonances. However, they can be significantly affected by the continuum part of the spectrum.

Shell model in the complex energy plane and two-particle resonances

An implementation of the shell-model to the complex energy plane is presented. The representation used in the method consists of bound single-particle states, Gamow resonances and scattering waves on the complex energy plane. Two-particle resonances are evaluated, and their structure in terms of the single-particle degrees of freedom is analyzed. It is found that two-particle resonances are mainly built upon bound states and Gamow resonances, but the contribution of the scattering states is also important.

Quasiparticle resonances in the BCS approach

Abstract We present a simple method for calculating the energies and the widths of quasiparticle resonant states in nuclei close to the driplines. The method is based on BCS equations written in the Berggren representation. In this representation the quasiparticle resonances are associated to the Gamow states of the mean field. The method is illustrated for the case of neutron-rich nuclei 20–22O and 84Ni.

Complex Quasiparticle Energy

We show how calculate the energies and the widths of quasiparticle resonant states without solving the complex bcs equations. The method is based on BCS equations solved in the real representation including the continuum. In this representation the quasiparticle resonances are associated to the Gamow states of the mean field.

A description of exotic nuclei by the aid of virtual states

A new unified shell model scheme is introduced in which the single particle basis is a generalization of the Berggren representation. This repesentation includes virtual i.e. antibound basis states as well. We apply the new scheme to the ground state of the exotic nucleus 11Li. Here the antibound pole and the complex continuum both have large contributions and neither of them can be neglected.

Complex shell model with antibound states

An unified shell model scheme to evaluate simultaneously the contributions of bound single-particle states, Gamow resonances, antibound (virtual) states and continuum complex scattering states is presented. The formalism could be very suitable to study processes occurring in the continuum part of the nuclear spectra.

Shell model representation with antibound states

The generalized Berggren representation treats antibound states on an equal footing with bound states and resonances. The advantage of this approach is that the effects of the antibound poles and the complex continuum can be studied separately. In order to show the power of the method we applied it for shell model problem with two valence neutrons for drip line nuclei.In the example of 11Li nucleus we generated the bound ground state from the unbound basis elements and observed that the antibound state is very important in the building up the halo. However the huge contribution of the antibound pole is partly canceled by that of the complex continuum. We predicted a two‐particle resonance in 11Li but for making more reliable predictions probably a more sophisticated model has to be used.