We present results of the time blocking approximation (TBA) on giant resonances in light, medium and heavy mass nuclei. The TBA is an extension of the widely used random-phase approximation (RPA) adding complex configurations by coupling to phonon excitations. A new method for handling the single-particle continuum is developed and applied in the present calculations. We investigate in detail the dependence of the numerical results on the size of the single particle space and the number of phonons as well as on nuclear matter properties. Our approach is self-consistent, based on an energy-density functional of Skyrme type where we used seven different parameter sets. The numerical results are compared with experimental data.

While bulk properties of stable nuclei are successfully reproduced by mean-field theories employing effective interactions, the dependence of the centroid energy of the electric giant dipole resonance on the nucleon number A is not. This problem is cured by considering many-particle correlations beyond mean-field theory, which we do within the Quasiparticle Time Blocking Approximation. The electric giant dipole resonance (GDR) is a wellknown nuclear excitation mode which is related to bulk properties of nuclei, such as the Thomas-Reiche-Kuhn (TRK) sum rule and the nuclear symmetry energy [1]. One might assume that theories which describe both bulk properties of nuclei and shell effects rather well, such as self-consistent mean-field theories based on effective nucleon interactions [2][3][4][5], should have no problem in systematically reproducing the centroid energies of the GDR as a function of the nucleon number A. This is not the case, however, as has been discussed in detail in several recent reviews on mean-field theories which include strength functions obtained within the quasiparticle random-phase approximation (QRPA) [6][7][8][9]. It was impossible so far to describe ground-state properties and the centroid energy of the GDR both in light and heavy nuclei with the same effective interaction. The problem is more serious than might appear at a first glance because the physics of the GDR is intimately related to the neutron skin thickness and the pygmy dipole strength [10][11][12], presently investigated experimentally because of an impact on the isotope abundance produced in supernova explosions [13]. There are two hints suggesting that the mean field approach by itself is at the origin of the problem. Complex configurations play a well-known role in the damping of nuclear excitations [14]. Even when effective interactions are fitted to the effective isoscalar mass, the symmetry energy, and the TRK sum rule enhancement factor κ, the problem remains unsolved [9].We employ the Quasiparticle Time Blocking Approximation (QTBA), developed and applied in [15][16][17][18][19][20][21], to study the GDR. The QTBA is a method to calculate nuclear response functions which generalizes the QRPA. It includes explicitly the coupling of one-particle onehole(1p1h) configuration with phonons, but omits the simultaneous excitation of two-phonon states in the presence of a 1p1h-excitation. In the limit of vanishing phonon-nucleon coupling, the QTBA corresponds to the QRPA, a standard mean field approach. Originally, the QTBA was used in the framework of Landau-Migdal theory, but has been generalized recently to effective interactions of the Skyrme family in order to make possible selfconsistent calculations [18,19,22]. The Skyrme interactions are defined by a set of momentum-and densitydependent contact interactions; different parameterizations may be distinguished by some set of theoretical quantities, such as nuclear matter properties or the effective mass, which are not directly observable. The momentum dependence of the ...

We have calculated the strength distributions of the giant monopole resonance in the even-A tin isotopes (A = 112 − 124) which were recently measured in inelastic α-scattering. The calculations were performed within two microscopic models: the quasiparticle random phase approximation (QRPA) and the quasiparticle time blocking approximation which is an extension of the QRPA including quasiparticle-phonon coupling. We used a self-consistent calculational scheme based on the HF+BCS approximation. The single-particle continuum was exactly included on the RPA level. The self-consistent mean field and the effective interaction were derived from the Skyrme energy functional. In the calculations, two Skyrme force parametrizations were used. The T5 parametrization with comparatively low value of the incompressibility of infinite nuclear matter (K ∞ = 202 MeV) gives theoretical results in good agreement with the experimental data including the resonance widths.