Effective interactions for the nuclear shell model

Various perturbative and non-perturbative many-body techniques are discussed in this work. Especially, we will focus on the summation of so-called Parquet diagrams with emphasis on applications to finite nuclei. Here, the subset of two-body Parquet equations will be discussed. A practical implementation of the corresponding equations for studies of effective interactions for finite nuclei is outlined.Comment: 55 pages, latex, to appear in Advances in many-body theory, vol

Gamow shell-model calculations of drip-line oxygen isotopes

We employ the Gamow shell model (GSM) to describe low-lying states of the oxygen isotopes 24O and 25O. The many-body Schrodinger equation is solved starting from a two-body Hamiltonian defined by a renormalized low-momentum nucleon-nucleon (NN) interaction, and a spherical Berggren basis. The Berggren basis treats bound, resonant, and continuum states on an equal footing, and is therefore an appropriate representation of loosely bound and unbound nuclear states near threshold. We show that such a basis is necessary in order to obtain a detailed and correct description of the low-lying 1+ and 2+ excited states in 24O. On the other hand, we find that a correct description of binding energy systematics of the ground states is driven by proper treatment and inclusion of many-body correlation effects. This is supported by the fact that we get 25O unstable with respect to 24O in both oscillator and Berggren representations starting from a 22O core. Furthermore, we show that the structure of these loosely bound or unbound isotopes are strongly influenced by the 1S0 component of the NN interaction. This has important consequences for our understanding of nuclear stability.Comment: 5 pages, 3 figure

Phase Transitions in Neutron Stars and Maximum Masses

Using the most recent realistic effective interactions for nuclear matter with a smooth extrapolation to high densities including causality, we constrain the equation of state and calculate maximum masses of rotating neutron stars. First and second order phase transitions to, e.g., quark matter at high densities are included. If neutron star masses of $\sim 2.3M_\odot$ from quasi-periodic oscillations in low mass X-ray binaries are confirmed, a soft equation of state as well as strong phase transitions can be excluded in neutron star cores.Comment: Replaced with revised version, 7 pages, 3 figs. To appear in Ap. J. Let

Generalized contour deformation method in momentum space: two-body spectral structures and scattering amplitudes

A generalized contour deformation method (GCDM) which combines complex rotation and translation in momentum space, is discussed. GCDM gives accurate results for bound, virtual (antibound), resonant and scattering states starting with a realistic nucleon-nucleon interaction. It provides a basis for full off-shell $t$-matrix calculations both for real and complex input energies. Results for both spectral structures and scattering amplitudes compare perfectly well with exact values for the separable Yamaguchi potential. Accurate calculation of virtual states in the Malfliet-Tjon and the realistic CD-Bonn nucleon-nucleon interactions are presented. GCDM is also a promising method for the computation of in-medium properties such as the resummation of particle-particle and particle-hole diagrams in infinite nuclear matter. Implications for in-medium scattering are discussed.Comment: 15 pages, revte

Hyperon properties in finite nuclei using realistic YNYN interactions

Single-particle energies of the $\Lambda$ and $\Sigma$ hyperons are obtained from the relevant self-energies. The latter are constructed within the framework of a perturbative many-body approach employing present realistic hyperon-nucleon interactions such as the models of the Juelich and Nijmegen groups. The effects of the non-locality and energy dependence of the self-energy on the bound states are investi- gated. It is also shown that, although the single-particle hyperon energies are well reproduced by local Woods-Saxon hyperon-nucleus potentials, the wave functions from the non-local self-energy are far more extended. Implications of this behavior on the mesonic weak decay of $\Lambda$ hypernuclei are discused.Comment: 31 pages, LateX, includes 4 PostScript figures, (submitted to Nucl. Phys. A

Quenching of spectroscopic factors for proton removal in oxygen isotopes

We present microscopic coupled-cluster calculations of the spectroscopic factors for proton removal from the closed-shell oxygen isotopes $^{14,16,22,24,28}$O with the chiral nucleon-nucleon interaction at next-to-next-to-next-to-leading order. We include coupling-to-continuum degrees of freedom by using a Hartree-Fock basis built from a Woods-Saxon single-particle basis. This basis treats bound and continuum states on an equal footing. We find a significant quenching of spectroscopic factors in the neutron-rich oxygen isotopes, pointing to enhanced many-body correlations induced by strong coupling to the scattering continuum above the neutron emission thresholds.Comment: 3 figure