[en] In this paper we report a study on the poles of the propagators of σ and ω mesons in the space-like region. In this region a zero sound can appear (a collective mode having a dispersion relation analogue to that obtained in sound propagation, but appearing at zero temperature) when the nucleon-nucleon interaction used is sufficiently repulsive. We have determined this zero sound by using a relativistic Hartree approximation, a model in which the vacuum fluctuations depend on a renormalization scale. Two renormalization schemes, corresponding to two different values of this scheme are physically acceptable. The first one corresponds to the relativistic Hartree approximation usually utilized, which minimizes the three and four body vacuum interactions. This leads to an incompressibility module which is two times higher than its experimental value. The second procedure minimizes the tree and four body interactions in the medium at saturation density, thus permitting the correct reproduction of the nuclear matter compressibility. We have shown that the zero sound which appears near the saturation density with the pure Hartree approximation occurs now at a density which is two times higher than the saturation density when the second choice of renormalization scale is done

[en] We review the present knowledge of multiphonon giant resonances in nuclei. Theoretical concepts approaching the intrinsic structure and excitation mechanisms of multi-phonon states are discussed. The available experimental results are summarized, including a brief description of applied techniques. This review emphasizes electromagnetic excitations of double dipole resonances. Open questions and possible routes toward a solution are addressed. (orig.)

[en] In heavy ion collisions at near relativistic energies, electromagnetic excitation of the double giant dipole resonance occurs with large cross sections. We summarize the presently available experimental data and discuss related theoretical efforts. Emphasis is paid to the question of anharmonicities and to the damping of the two-phonon states. (orig.)

[en] The nuclear level density parameters of the stable nuclides have been determined from the neutron resonance data on the basis of new values for the spin dispersion parameter. The latter parameter is deduced from the spin dependent average level spacings of s-wave neutron resonances of odd target nuclides. In addition, the temperature dependence of the level density parameter is studied and an analytical relation for it is presented

[en] Calculations of nuclear density levels parameter in dependence of temperature T - a(T) was made and compared with results of recent experiments which show that the value of a diminishes from A/8 at T congruent 0 to A/13 at T congruent 5 MeV (here A is the mass number)

No abstract available

No abstract available

No abstract available

No abstract available

No abstract available