H. Müther

The 0 nu bb-decay nuclear matrix elements with self-consistent short-range correlations

A self-consistent calculation of nuclear matrix elements of the neutrinoless double-beta decays (0{nu}{beta}{beta}) of {sup 76}Ge, {sup 82}Se, {sup 96}Zr, {sup 100}Mo, {sup 116}Cd, {sup 128}Te, {sup 130}Te, and {sup 136}Xe is presented in the framework of the renormalized quasiparticle random phase approximation (RQRPA) and the standard QRPA. The pairing and residual interactions as well as the two-nucleon short-range correlations are for the first time derived from the same modern realistic nucleon-nucleon potentials, namely, from the charge-dependent Bonn potential (CD-Bonn) and the Argonne V18 potential. In a comparison with the traditional approach of using the Miller-Spencer Jastrow correlations, matrix elements for the 0{nu}{beta}{beta} decay are obtained that are larger in magnitude. We analyze the differences among various two-nucleon correlations including those of the unitary correlation operator method (UCOM) and quantify the uncertainties in the calculated 0{nu}{beta}{beta}-decay matrix elements.

Two-body correlations in nuclear systems

Abstract Correlations in the nuclear wave-function beyond the mean-field or Hartree-Fock approximation are very important to describe basic properties of nuclear structure. Various approaches to account for such correlations are described and compared to each other. This includes the holeline expansion, the coupled cluster or “exponential S” approach, the self-consistent evaluation of Greens functions, variational approaches using correlated basis functions and recent developments employing quantum Monte-Carlo techniques. Details of these correlations are explored and their sensitivity to the underlying nucleon-nucleon interaction. Special attention is paid to the attempts to investigate these correlations in exclusive nucleon knock-out experiments induced by electron scattering. Another important issue of nuclear structure physics is the role of relativistic effects as contained in phenomenological mean field models. The sensitivity of various nuclear structure observables on these relativistic features are investigated. The report includes the discussion of nuclear matter as well as finite nuclei.

The quasiparticle interaction, a shield of nuclear matter against pion condensation

Abstract A microscopic calculation is presented for the quasiparticle interaction in nuclear matter. As a starting point a Brueckener G-matrix is used, which is derived from realistic potentials (Reid soft core, HM2Δ). Keeping the full complexity of this interaction, the excitation modes for the different spin-isospin channels are evaluated. The effects of isobar excitation [Δ(3, 3)] are also taken into account. The exchange of the corresponding phonons is added to the bare G-matrix and the influence of this so-called crossed channel renormalization on the interaction of quasiparticles at the Fermi surface is discussed. This renormalization of the particle-hole interaction increases drastically the critical density for pion condensation in nuclear matter.

Nucleon properties in the nuclear medium

Recent developments in the many-body theory of interacting fermions are discussed employing a self-consistent Green function approach. This scheme is outlined and its application to nuclear systems is presented. Special attention is paid to the consistent inclusion of short-range and long-range correlations induced by realistic nucleon-nucleon interactions. Such correlations lead to occupation probabilities which deviate from the simple mean-field or shell-model description. The scheme is extended to incorporate relativistic effects. Also applications of field theoretical models for hadrons in a nuclear medium and their relation to QCD are discussed.

The screening of the particle-hole interaction to all orders☆

Abstract Starting from Brueckners G -matrix the effects of the induced interactions on the particle-hole interaction in nuclear matter are investigated to all orders. Although an iterative solution of the non-linear integral equations, which have to be solved, leads to divergent contributions, it can be shown that the renormalization effects summed to all orders are finite. The complete momentum dependence of the particle-hole interaction is treated which in the Landau limit results in less attractive F 0 and more repulsive G ′ 0 parameters. For finite ph momenta these features are maintained implying that the collectivity in the pion spin-isospin channel is screened also when the renormalization is considered to all orders.

Modern nucleon-nucleon potentials and symmetry energy in infinite matter

Abstract We study the symmetry energy in infinite nuclear matter employing a non-relativistic Brueckner-Hartree-Fock approach and using various new nucleon-nucleon (NN) potentials, which fit np and pp scattering data very accurately. The potential models we employ are the recent versions of the Nijmegen group, Nijm-I, Nijm-II, and Reid93, the Argonne V18 potential and the CD-Bonn potential. All these potentials yield a symmetry energy which increases with density, resolving a discrepancy that existed for older NN potentials. The origin of remaining differences is discussed.

Correlations in hot asymmetric nuclear matter

The single-particle spectral functions in asymmetric nuclear matter are computed using the ladder approximation within the theory of finite temperature Greens functions. The internal energy and the momentum distributions of protons and neutrons are studied as a function of the density and the asymmetry of the system. The proton states are more strongly depleted when the asymmetry increases whereas the occupation of the neutron states is enhanced compared to the symmetric case. The self-consistent Greens function approach leads to slightly smaller energies compared to the Brueckner-Hartree-Fock approach. This effect increases with density and thereby modifies the saturation density and leads to smaller symmetry energies.

Self-consistent solution to the nuclear many-body problem at finite temperature

The properties of symmetric nuclear matter are investigated within Greens functions approach. We have implemented an iterative procedure allowing for a self-consistent evaluation of the single-particle and two-particle propagators. The in-medium scattering equation is solved for a realistic (nonseparable) nucleon-nucleon interaction including both particle-particle and hole-hole propagation. The corresponding two-particle propagator is constructed explicitly from the single-particle spectral functions. Results are obtained for finite temperatures and an extrapolation to

Spontaneous breaking of rotational symmetry in superconductors

T=0

Correlations and the Dirac structure of the nucleon self-energy

is presented.