[en] A mapping procedure which has applied both for the deriving boson images of fermion operators and for constructing nucleon images of quark operators within the framework of nonrelativistic quark model is illustrated

[en] The collective pair model extended the collective pair approximation. It includes collective correlated particle-particle pairs, as well as a couple of collective correlated particle-hole pairs with collective correlated particle-particle pairs. Meanwhile, it includes isospin quantum number

[en] Short communication. 2 refs., 1 fig

[en] Difficulties in the standard Random Phase Approximation (RPA) are discussed. Previous attempt to eliminate the inconsistency due to uncorrelated HF ground state are shortly reviewed and some results are presented. A new approach is proposed to go further towards a self-consistent RPA. Finally some results on metallic clusters are presented, using a simplified version of the approach which requires less computational effort. It represents a significant improvement over the methods used so far

[en] Starting from a microscopic approach based on RPA, we go beyond it by introducing anharmonicity by taking into account the mixing of two-phonon states among themselves and with one-phonon states. By introducing also non linear terms in the external field we show that these new ingredients give an explanation of the puzzle of the excitation cross section of the double giant dipole resonance (DGDR) for the ²⁰⁸Pb + ²⁰⁸Pb system at 641 MeV/A

[en] The authors present some results on the properties of ⁶Li described as 2p-2n and 1p-1n substructures whose intrinsic wave functions are determined, in a shell-model basis, as those minimizing the g.s. energy of ⁶Li. The calculation is completely microscopic in the sense that antisymmetrization is fully taken into account and that one starts from a bare nucleon-nucleon interaction. Very good agreement with experimental data on the ground state energy and electric form factor is achieved without any adjustable parameter. A relevant result seems to be the large 1s component of the intercluster wave function. (Auth.)

No abstract available

[en] We apply boson expansion methods to an extended exactly solvable Lipkin-Meshkov-Glick model including anharmonicities in analogy with previous microscopic calculations. We study the effects of different approximations present in these calculations, among which the truncation of the Hamiltonian and of the space, in connection with the study of the properties of two-phonon states. By comparing the approximate results on the spectrum with the exact ones we conclude that the approximations made in the microscopic calculations on two-phonon states are well justified. We find also that a good agreement with the exact results for the three-phonon state is obtained by using a bosonic Hamiltonian truncated at the fourth order. This result makes us confident that such approximation can be used in future realistic calculations, thus allowing a theoretical study of triple excitations of giant resonances

[en] Conclusion proved that if the authors calculate ¹⁸O collective spectra in terms of the Collective Pair Model, the authors can get the positive low laying levels of ¹⁸O which are of the particle particle pair, independent on the excitation of hole within closed shell. 1^- low laying levels are of non-collective 3 particle 1 hole states. 1^- fourth level is of collective 3 particle 1 hole states. 3^- low laying levels are of collective 3 particle 1 hole states. 1^-, 3^- low laying levels agree very well with the experiment data. Hence the TDA is sufficient for the calculations of 1^-,3^- collective low levels of ¹⁸O

[en] Regularization techniques, well known in QFT, are applied to nuclear physics, in the presence of a nucleon-meson interaction, in order to extract a finite part from the divergent nucleon self-energy Feynman integral. Explicit calculations in the case of the ¹⁶O nucleus have been carried out