NEW ASPECTS ON DYNAMICS IN NUCLEI DESCRIBED BY COVARIANT DENSITY FUNCTIONAL THEORY

Abstract

The description of nuclear dynamics in the framework of Covariant Density Functional Theory (CDFT) is based on the Relativistic Random Phase Approximation (RRPA) or, in superfluid systems, on the Relativistic Quasi-particle RPA (RQRPA). This method has been used in the past extensively for the calculation of many kinds of resonances in spherical systems. Here we report on an extensions of this method: a new relativistic QRPA code has been developed for the description of deformed systems and first applications for the description of E1 pygmy modes and M1 scissor-like excitations are presented. New experimental facilities with radioactive nuclear beams make it possible to investigate the nuclear chart not only along the narrow line of stable isotopes but also in areas of large neutron- and proton excess far from the valley of -stability. Low-lying collective dipole excitations are expected to play an important role in astrophysical applications in neutron rich systems, where the presence of a lowlying resonant component of the E1 strength has a strong influence on the radiative neutron-capture rates in the r-process. 1 This situation has stimulated enhanced efforts on the theoretical side to understand the dynamics of the nuclear many-body problem by microscopic methods. For the large majority of medium heavy and heavy nuclei, a quantitative microscopic description is only possible by density functional theory. Although this theory can, in principle, provide an exact description of the many-body dynamics 2 if the exact density functional is known, in nuclear physics one is far from a microscopic derivation of this functional. The most successful schemes use a phenomenological ansatz incorporating as many symmetries of the system as possible and adjust the parameters of these functionals to ground state properties of characteristic nuclei all over the periodic table. Of particular interest are covariant density functionals 3,4 because they are based on Lorentz invariance. This symmetry not only allows to describe the spin-orbit coupling in a consistent way which has an essential influence on the underlying shell, but it also put stringent restrictions on the number of parameters in the corresponding functionals without reducing the quality of the agreement with experimental data. A