Elena Litvinova

Mode Coupling and the Pygmy Dipole Resonance in a Relativistic Two-Phonon Model

A new class of many-body models, based on covariant density functional theory for excited states, is presented. It allows a parameter free description of the fragmentation of nuclear states induced by mode coupling of two-quasiparticle and two-phonon configurations. As compared to earlier methods it provides a consistent and parameter free theory of the fine structure of nuclear resonances. The method is applied very successfully to investigate the newly discovered low-lying dipole excitations in Sn and Ni isotopes with large neutron excess.

Fragmentation of spin-dipole strength in 90Zr and 208Pb

An extension of time-dependent covariant density functional theory that includes particle–vibration coupling is applied to the charge-exchange channel. Spin-dipole excitation spectra are calculated an compared to available data for 90Zr and 208Pb. A significant fragmentation is found for all three angular-momentum components of the spin-dipole strength as a result of particle–vibration coupling, as well as a shift of a portion of the strength to higher energy. A high-energy tail is formed in the strength distribution that linearly decreases with energy. Using a model-independent sum rule, the corresponding neutron skin thickness is estimated and shown to be consistent with values obtained at the mean-field level.

Quasiparticle time blocking approximation in coordinate space as a model for the damping of the giant dipole resonance

The quasiparticle time blocking approximation (QTBA) is applied to describe E1 excitations in the even-even tin isotopes. Within the model pairing correlations, twoquasiparticle (2q), and 2q⊗phonon configurations are included. Thus the QTBA is an extension of the quasiparticle random phase approximation to include quasiparticlephonon coupling. Calculational formulas are presented in case of neutral excitations in the spherically symmetric system. The main equations are written in the coordinate representation that allows to take into account single-particle continuum completely. The E1 photoabsorption cross sections have been calculated in nuclei 116,120,124Sn. It has been obtained that the 2q⊗phonon configurations provide noticeable fragmentation of the giant dipole resonance resulting in appearance of significant spreading width. The results are compared with available experimental data. PACS numbers: 21.60.-n, 24.30.Cz, 25.20.Dc, 27.60.+j

Spin-orbit splittings of neutron states in N=20 isotones from covariant density functionals and their extensions

Konstantinos Karakatsanis, ∗ G. A. Lalazissis, Peter Ring, and Elena Litvinova 4 Physics Department, Aristotle University of Thessaloniki, Thessaloniki GR-54124, Greece Physik Department, Technische Universität Munchen, D-85747 Garching, Germany Department of Physics, Western Michigan University, Kalamazoo MI 49008-5252 USA National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, MI 48824-1321, USA (Dated: May 10, 2017)

Isospin dynamics in nuclear structure

We discuss some special aspects of the nuclear many-body problem related to isospin transfer. The major quantity of interest is the in-medium propagator of a particle-hole configuration of the proton-neutron character, which determines the nuclear response to isospin transferring external fields. One of the most studied excitation modes is the Gamow-Teller resonance (GTR), which can, therefore, be used as a sensitive test for the theoretical approaches. Its low-energy part, which is responsible for the beta decay half-lives, is especially convenient for this. Models benchmarked against the GTR can be used to predict other, more exotic, excitations studied at nuclear rare isotope beam facilities and in astrophysics. As far as the precision is concerned, the major problem in such an analysis is to disentangle the effects related to the underlying interaction and those caused by the many-body correlations. Therefore, approaches (i) based on fundamental concepts for the nucleon-nucleon interaction which (ii) include complex many-body dynamics are the preferred ones. We discuss progress and obstacles on the way to such approaches.

Quasiparticle-vibration coupling effects on nuclear transitions of astrophysical interest

The relativistic quasiparticle time-blocking approximation (RQTBA) is applied to the description of nuclear excitation modes of astrophysical interest. This method is based on the meson-nucleon Lagrangian and goes beyond the standard relativistic quasiparticle random-phase approximation (RQRPA) by treating the coupling between single quasiparticles and collective vibrations of the nucleus. We calculate electric dipole transitions and Gamow-Teller modes in the (p,n) direction in a few Sn isotopes and obtain the rates of (n,

Effects of meson-nucleon dynamics in a relativistic approach to medium-mass nuclei

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Hauser-Feshbach reaction rates with parity-dependent level densities

) reaction and

Dynamics of Exotic Nuclear Systems: Covariant QRPA and Extensions.

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Relativistic Approach To Nuclear Spin-isospin Excitations Including Quasiparticle-vibration Coupling

-decay processes, which govern the r-process nucleosynthesis, in a unified RQTBA framework. Gamow-Teller transitions in the (n,p) branch, which in principle can serve for the modeling of stellar evolution, are also investigated, and