Nuclear pairing from chiral pion-nucleon dynamics

We use a recently improved version of the chiral nucleon-nucleon potential at next-to-next-to-leading order to calculate the $^1S_0$ pairing gap in isospin-symmetric nuclear matter. The pairing potential consists of the long-range one- and two-pion exchange terms and two short-distance NN-contact couplings. We find that the inclusion of the two-pion exchange at next-to-next-to-leading order reduces substantially the cut-off dependence of the $^1S_0$ pairing gap determined by solving a regularised BCS equation. Our results are close to those obtained with the universal low-momentum nucleon-nucleon potential $V_{\rm low-k}$ or the phenomenological Gogny D1S force.Comment: 9 pages, 3 eps figures, submitted to PR

Renormalized relativistic Hartree-Bogoliubov equations with a zero-range pairing interaction

A recently introduced scheme for the renormalization of the Hartree-Fock-Bogoliubov equations in the case of zero-range pairing interaction is extended to the relativistic Hartree-Bogoliubov model. A density-dependent strength parameter of the zero-range pairing is adjusted in such a way that the renormalization procedure reproduces the empirical $^1S_0$ pairing gap in isospin-symmetric nuclear matter. The model is applied to the calculation of ground-state pairing properties of finite spherical nuclei.Comment: 13 pages, 8 figures, accepted for publication in Physical Review

Beyond the relativistic Hartree mean-field approximation: energy dependent effective mass

The standard relativistic mean-field model is extended by including dynamical effects that arise in the coupling of single-nucleon motion to collective surface vibrations. A phenomenological scheme, based on a linear ansatz for the energy dependence of the scalar and vector components of the nucleon self-energy for states close to the Fermi surface, allows a simultaneous description of binding energies, radii, deformations and single-nucleon spectra in a self-consistent relativistic framework. The model is applied to the spherical, doubly closed-shell nuclei 132Sn and 208Pb.Comment: 14 pages, 2 figures; replaced with revised versio

Toroidal dipole resonances in the relativistic random phase approximation

The isoscalar toroidal dipole strength distributions in spherical nuclei are calculated in the framework of a fully consistent relativistic random phase approximation. It is suggested that the recently observed "low-lying component of the isoscalar dipole mode" might in fact correspond to the toroidal giant dipole resonance. Although predicted by several theoretical models, the existence of toroidal resonances has not yet been confirmed in experiment. The strong mixing between the toroidal resonance and the dipole compression mode might help to explain the large discrepancy between theory and experiment on the position of isoscalar giant dipole resonances.Comment: 10 pages, 3 figures; Phys.Rev.C, in prin

Relativistic description of exotic collective excitation phenomena in atomic nuclei

The low-lying dipole and quadrupole states in neutron rich nuclei, are studied within the fully self-consistent relativistic quasiparticle random-phase approximation (RQRPA), formulated in the canonical basis of the Relativistic Hartree-Bogoliubov model (RHB), which is extended to include the density dependent interactions. In heavier nuclei, the low-lying E1 excited state is identified as a pygmy dipole resonance (PDR), i.e. as a collective mode of excess neutrons oscillating against a proton-neutron core. Isotopic dependence of the PDR is characterized by a crossing between the PDR and one-neutron separation energies. Already at moderate proton-neutron asymmetry the PDR peak is calculated above the neutron emission threshold, indicating important implications for the observation of the PDR in (gamma,gamma') scattering, and on the theoretical predictions of the radiative neutron capture rates in neutron-rich nuclei. In addition, a novel method is suggested for determining the neutron skin of nuclei, based on measurement of excitation energies of the Gamow-Teller resonance relative to the isobaric analog state.Comment: 8 pages, 3 figures, invited talk at the international workshop "Blueprints for the nucleus: From First Principles to Collective Motion", May 17-22. 2004, Istanbul, Turkey; to appear in Int. J. Mod. Phys.

Microscopic description of nuclear quantum phase transitions

The relativistic mean-field framework, extended to include correlations related to restoration of broken symmetries and to fluctuations of the quadrupole deformation, is applied to a study of shape transitions in Nd isotopes. It is demonstrated that the microscopic self-consistent approach, based on global effective interactions, can describe not only general features of transitions between spherical and deformed nuclei, but also the singular properties of excitation spectra and transition rates at the critical point of quantum shape phase transition.Comment: 10 pages, 4 figures, accepted for publication in Physical Review Letter

Partial Dynamical Symmetry and Anharmonicity in Gamma-Soft Nuclei

Partial dynamical symmetry is shown to be relevant for describing the anharmonicity of excited bands in $^{196}$Pt while retaining solvability and good SO(6) symmetry for the ground band.Comment: 4 pages, 1 figure, Proc. Int. Conf. on "Nuclear Structure and Dynamics", May 4-8, 2009, Dubrovnik, Croati