arXiv subjects

H. Müther

Publications and source records attributed to H. Müther.

76 records · Page 5Linked to original sources

arXiv1993

Determination of Dipole Polarization Effects in $^7$Li and $^{11}$Li

The structure of $^6$Li, $^7$Li and $^{11}$Li nuclei is investigated in a model space which includes all configurations with oscillator energy up to $3\hbarω$ above the ground state configuration. The energy spectra and electromagnetic properties of the low-lying states are determined with various two-body interactions, which are derived from the Bonn potential. The results of these shell-model calculations depend on the strength of the tensor component contained in the NN interaction and also on the treatment of the Dirac spinors for the nucleons in the nuclear medium. In addition the calculation determines the {\it dipole polarizability} of $^7$Li and $^{11}$Li caused from virtual $E1$ excitations to the positive parity states of these nuclei. It is demonstrated that the BAGEL scheme provides a very powerful tool to consider contributions from virtual excitations up to large energies.

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arXiv1993

Nambu-Jona-Lasinio Models Beyond the Mean Field Approximation

Inspired by the model of Nambu and Jona-Lasinio, various Lagrangians are considered for a system of interacting quarks. Employing standard techniques of many-body theory, the scalar part of the quark self-energy is calculated including terms up to second-order in the interaction. Results obtained for the single-particle Green's function are compared with those which only account for the mean-field or Hartree-Fock term in the self-energy. Depending on the explicit form of the Lagrangian, the second-order contributions range between 4 and 90 percent of the leading Hartree-Fock term. This leads to a considerable momentum dependence of the self-energy and the effective mass of the quarks.

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arXiv1993

Correlations in Nuclei: Self-Consistent Treatment and the BAGEL Approach

An approach is presented which allows a self-consistent description of the fragmentation of single-particle strength for nucleons in finite nuclei employing the Greens function formalism. The self-energy to be considered in the Dyson equation for the single-particle Greens function contains all terms of first (Hartree-Fock) and second order in the residual interaction. It is demonstrated that the fragmentation of the single-particle strength originating from the terms of second order can efficiently be described in terms of the so-called BAGEL approximation. Employing this approximation the self-energy can be evaluated in a self-consistent way, i.e. the correlations contained in the Greens function are taken into account for the evaluation of the self-energy. As an example this scheme is applied to the nucleus $^{16}O$, using a realistic nucleon nucleon interaction. The effects of the correlations on the occupation probabilities and the binding energy are evaluated.

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arXiv1993

Medium corrections to the tensor interaction in nuclei: Energy difference of T=1 and T=0 J=0- states in 16O

It has been shown in the past that in a shell model calculation, restricted to 1Hbar*Omega 1p-1h configurations, the energy splitting between the lowest J=0-, T=0 and J=0-, T=1 states in 16O is mainly due to the tensor component of the nucleon-nucleon interaction. In this work, we extend the calculation to include 3Hbar*Omega 2p-2h and 3p-3h configurations. We use realistic G matrices derived from various One-Boson-Exchange potentials taking into account the effects of the Dirac-Brueckner-Hartree-Fock approach, i.e., a modification of the Dirac spinors for the nucleons in the medium. It is found that the splitting is rather sensitive to the long-range components of the isovector tensor force. The splitting is reduced considerably by including 2p-2h configurations, in particular.

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