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H. Müther

Publications and source records attributed to H. Müther.

At least 37 records · Page 2Linked to original sources
arXiv2007

Nuclear matter in the crust of neutron stars

The properties of inhomogeneous nuclear matter are investigated considering the self-consistent Skyrme Hartree-Fock approach with inclusion of pairing correlations. For a comparison we also consider a relativistic mean field approach. The inhomogeneous infinite matter is described in terms of cubic Wigner-Seitz cells, which leads to a smooth transition to the limit of homogeneous nuclear matter. The possible existence of various structures in the so-called pasta phase is investigated within this self-consistent approach and a comparison is made to results obtained within the Thomas-Fermi approximation. Results for the proton abundances and the pairing properties are discussed for densities for which clustering phenomena are obtained.

nucl-th↗
arXiv2006

Correlations and effective interactions in nuclear matter

We performed Self-Consistent Greens Function (SCGF) calculations for symmetric nuclear matter using realistic nucleon-nucleon (NN) interactions and effective low-momentum interactions ($V_{low-k}$), which are derived from such realistic NN interactions. We compare the spectral distributions resulting from such calculations. We also introduce a density-dependent effective low-momentum interaction which accounts for the dispersive effects in the single-particle propagator in the medium.

nucl-th↗
arXiv2005

Pairing properties of nucleonic matter employing dressed nucleons

A survey of pairing properties of nucleonic matter is presented that includes the off-shell propagation associated with short-range and tensor correlations. For this purpose, the gap equation has been solved in its most general form employing the complete energy and momentum dependence of the normal self-energy contributions. The latter correlations include the self-consistent calculation of the nucleon self-energy that is generated by the summation of ladder diagrams. This treatment preserves the conservation of particle number unlike approaches in which the self-energy is based on the Brueckner-Hartree-Fock approximation. A huge reduction in the strength as well as temperature and density range of ${}^3S_1$-${}^3D_1$ pairing is obtained for nuclear matter as compared to the standard BCS treatment. Similar dramatic results pertain to ${}^1S_0$ pairing of neutrons in neutron matter.

nucl-th↗
arXiv2004

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 Green's 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 while the occupation of the neutron states is enhanced as compared to the symmetric case. The self-consistent Green's function approach leads to slightly smaller energies as compared to the Brueckner Hartree Fock approach. This effect increases with density and thereby modifies the saturation density and leads to smaller symmetry energies.

nucl-th↗
arXiv2004

A symmetry-projected variational approach to the 1-dimensional Hubbard-model

We apply a variational method devised for the nuclear many--body problem to the 1-dimensional Hubbard--model with nearest neighbor hopping and periodic boundary conditions. The test wave function consist for each state out of a single Hartree--Fock determinant mixing all the sites (or momenta) as well as the spin--projections of the electrons. Total spin and linear momentum are restored by projection methods before the variation. It is demonstrated that this approach reproduces the results of exact diagonalisations for half--filled N=12 and N=14 lattices not only for the energies and occupation numbers of the ground but also of the lowest excited states rather well. Furthermore, a system of 10 electrons in a N=12 lattice is investigated and, finally, a N=30 lattice is studied. In addition to energies and occupation numbers we present the spectral functions computed with the help of the symmetry--projected wave functions, too. Also here nice agreement with the exact results (where available) is reached.

cond-mat.str-el↗
arXiv2004

Correlated nucleons in configuration space

Several recent studies have dealt with the effects of short range correlations on the momentum distribution of nucleons in nuclei. Here we investigate the correlation effects on the density and spectral distribution in coordinate space. A combination of experimental data and spectral functions calculated from realistic N-N interactions allows us to resolve a recently uncovered discrepancy with occupation of quasi-particle states derived from (e,e'p) data.

nucl-th↗
arXiv2004

Correlations and spectral functions in asymmetric nuclear matter

The self-energy of nucleons in asymmetric nuclear matter is evaluated employing different realistic models for the nucleon-nucleon interaction. Starting from the Brueckner Hartree Fock approximation without the usual angle-average in the two-nucleon propagator the effects of the hole-hole contributions are investigated within the self-consistent Green's function approach. Special attention is paid to the isospin-dependence of correlations, which can be deduced from the spectral functions of nucleons in asymmetric matter. The strong components of the proton - neutron interaction lead in neutron-rich matter to a larger depletion for the occupation probability of proton states below the Fermi momentum.

nucl-th↗
arXiv2004

Spectral function at high missing energies and momenta

The nuclear spectral function at high missing energies and momenta has been determined from a self-consistent calculation of the Green's function in nuclear matter using realistic nucleon-nucleon interactions. The results are compared with recent experimental data derived from ($e,e'p$) reactions on $^{12}C$. A rather good agreement is obtained if the Green's functions are calculated in a non-perturbative way.

nucl-th↗
arXiv2004

Spontaneous breaking of rotational symmetry in superconductors

We show that homogeneous superconductors with broken spin/isospin symmetry lower their energy via a transition to a novel superconducting state where the Fermi-surfaces are deformed to a quasi-ellipsoidal form at zero total momentum of Cooper pairs. In this state, the gain in the condensation energy of the pairs dominates over the loss in the kinetic energy caused by the lowest order (quadrupole) deformation of Fermi-surfaces from the spherically symmetric form. There are two energy minima in general, corresponding to the deformations of the Fermi-spheres into either prolate or oblate forms. The phase transition from spherically symmetric state to the superconducting state with broken rotational symmetry is of the first order.

cond-mat.supr-con↗
arXiv2004

Mean field and pairing properties in the crust of neutron stars

Properties of the matter in the inner crust of a neutron star are investigated in a Hartree-Fock plus BCS approximation employing schematic effective forces of the type of the Skyrme forces. Special attention is paid to differences between a homogenous and inhomogeneous description of the matter distribution. For that purpose self-consistent Hartree Fock calculations are performed in a spherical Wigner-Seitz cell. The results are compared to predictions of corresponding Thomas Fermi calculations. The influence of the shell structure on the formation of pairing correlations in inhomogeneous matter are discussed.

nucl-th↗
arXiv2003

A Self-Consistent Solution to the Nuclear Many-Body Problem at Finite Temperature

The properties of symmetric nuclear matter are investigated within the Green's 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 (non-separable) nucleon-nucleon interaction including both particle-particle and hole-hole propagation. The corresponding two-particle propagator is constructed explicitely from the single-particle spectral functions. Results are obtained for finite temperatures and an extrapolation to T=0 is presented.

nucl-th↗
arXiv2003

Breaking rotational symmetry in two-flavor color superconductors

The color superconductivity under flavor asymmetric conditions relevant to the compact star phenomenology is studied within the Nambu-Jona-Lasinio model. We focus on the effect of the deformation of the Fermi surfaces on the pairing properties and the energy budget of the superconducting state. We find that at finite flavor asymmetries the color superconducting BCS state is unstable towards spontaneous quadrupole deformation of the Fermi surfaces of the $d$ and $u$ quarks into ellipsoidal form. The ground state of the phase with deformed Fermi surfaces corresponds to a superposition of prolate and oblate deformed Fermi ellipsoids of $d$ and $u$ quarks.

hep-ph↗
arXiv2002

The structure of nuclear systems derived from low momentum nucleon-nucleon potentials

Various nuclear structure observables are evaluated employing low-momentum nucleon-nucleon (NN) potentials $V_{\rm low-k}$ derived from the CD-Bonn and Nijmegen NN interactions $V_{NN}$. By construction, the high momentum modes of the original $V_{NN}$ are integrated out in $V_{\rm low-k}$, with the requirement that the deuteron binding energy and low energy phase shifts of $V_{NN}$ are exactly reproduced. Using this interaction, we evaluate the bulk properties (binding energy and saturation density) of nuclear matter and finite nuclei, in particular their dependence on the cut-off parameter. We also study the pairing gap and the residual interaction in nuclear matter in terms of the Landau parametrization. At low and medium densities, the HF and BHF binding energies for nuclear matter calculated with the $V_{\rm low-k}$'s derived from the CD-Bonn and Nijmegen potentials are nearly identical. The pairing gaps and Landau parameters derived from $V_{\rm low-k}$ are remarkably close to those given by the full-space $V_{NN}$. The $V_{\rm low-k}$ interactions, however, fail to reproduce the saturation property of nuclear matter at higher densities if the cut-off for the high momentum modes is assumed density independent.

nucl-th↗
arXiv2002

Ground state of finite nuclei evaluated from realistic interactions

Ground state properties of finite nuclei ($^{16}$O and $^{40}$Ca) are evaluated from realistic nucleon-nucleon interactions. The calculations are based on the Brueckner-Hartree-Fock approximation. Special attention is paid to the role of the energy spectrum for the particle states, in particular for those close to the Fermi energy. Additional binding energy is obtained from the inclusion of the hole-hole scattering term within the framework of the Green function approach. Results for the energy distribution of the single-particle strength and the sensitivity to the nucleon-nucleon interaction are investigated. For that purpose three modern nucleon-nucleon interactions are employed: the Argonne V18, the charge dependent Bonn potential and a realistic nucleon-nucleon interaction which is based on chiral perturbation theory and which has recently been fitted by the Idaho group.

nucl-th↗
arXiv2002

Interaction induced deformation in momentum distribution of spin polarized nuclear matter

Effects of spin polarization on the structure of symmetric nuclear matter and pure neutron matter are investigated. We show that the spin polarization induces a deformation of the Fermi spheres for nucleons with spin parallel and opposite to the polarization axes. This feature can be related to the structure of the one pion exchange contribution to a realistic nucleon-nucleon interaction. While the anisotropies in the momentum distribution lower the energy of the system by small amount, the associated variations of the single particle energies with the angle between the polarization axis and the particle momentum are significant.

nucl-th↗
arXiv2001

Nuclear Self-energy and Realistic Interactions

The structure of nucleon self-energy in nuclear matter is evaluated for various realistic models of the nucleon-nucleon (NN) interaction. Starting from the Brueckner-Hartree-Fock approximation without the usual angle-average approximation, the effects of hole-hole contributions and a self-consistent treatment within the framework of the Green function approach are investigated. Special attention is paid to the predictions for the spectral function originating from various models of the NN interaction which all yield an accurate fit for the NN phase shifts.

nucl-th↗
arXiv2001

$Δ(1232)$ Isobar Excitations and the Ground State of Nuclei

The influence of $Δ$ isobar components on the ground state properties of nuclear systems is investigated for nuclear matter as well as finite nuclei. Many-body wave functions, including isobar configurations, and binding energies are evaluated employing the framework of the coupled-cluster theory. It is demonstrated that the effect of isobar configurations depends in a rather sensitive way on the model used for the baryon-baryon interaction. As examples for realistic baryon-baryon interactions with explicit inclusion of isobar channels we use the local ($V28$) and non-local meson exchange potentials (Bonn$_{2000}$) but also a model recently developed by the Salamanca group, which is based on a quark picture. The differences obtained for the nuclear observables are related to the treatment of the interaction, the $π$-exchange contributions in particular, at high momentum transfers.

nucl-th↗