Low-lying continuum states of drip-line Oxygen isotopes

Low-lying continuum states of exotic oxygen isotopes are studied, by introducing the Continuum-Coupled Shell Model (CCSM) characterized by an infinite wall placed very far and by an interaction for continuum coupling constructed in a close relation to realistic shell-model interaction. Neutron emission spectra from exotic oxygen isotopes are calculated by the doorway-state approach in heavy-ion multi-nucleon transfer reactions. The results agree with experiment remarkably well, as an evidence that the continuum effects are stronger than $\sim$1 MeV, consistently with the shell evolution in exotic nuclei. The results by this CCSM doorway-state approach are compared with calculations on neutron-scattering resonance peaks made within the CCSM phase-shift approach and also with those obtained in the Gamow shell model, by taking the same interaction. Remarkable similarities in peak energies and certain differences in widths are then obtained.Comment: This paper has been withdrawn by the author due to the publication in PTEP journal with considerable expansion. The re-submission to arXiv has been given up due to the differences in style files, et

Novel features of nuclear forces and shell evolution in exotic nuclei

Novel simple properties of the monopole component of the effective nucleon-nucleon interaction are presented, leading to the so-called monopole-based universal interaction. Shell structures are shown to change as functions of $N$ and $Z$ consistently with experiments. Some key cases of this shell evolution are discussed, clarifying the effects of central and tensor forces. The validity of the present tensor force is examined in terms of the low-momentum interaction V$_{low k}$ and the Q$_{box}$ formalism.Comment: 4 pages, 4 figure

In-medium similarity renormalization group for open-shell nuclei

We present a nonperturbative derivation of effective valence-shell Hamiltonians in the framework of the recently developed in-medium similarity renormalization group (IM-SRG). As a first application, we calculate the spectra of $p$- and $sd$-shell nuclei, $^6$Li and $^{18}$O, based on evolved chiral nucleon-nucleon interactions. For $^6$Li, the spectrum is in very good agreement with ab-initio results. For $^{18}$O, the IM-SRG provides a new method for the shell model to systematically go beyond effective interaction techniques based on diagrammatic expansions.Comment: 4 pages, 5 figure

Renormalization persistency of the tensor force in nuclei

In this work we analyze the tensor-force component of effective interactions appropriate for nuclear shell-model studies, with particular emphasis on the monopole term of the interactions. Standard nucleon-nucleon ( NN ) interactions such as AV8’ and χ N 3 LO are tailored to shell-model studies by employing V low k techniques to handle the short-range repulsion of the NN interactions and by applying many-body perturbation theory to incorporate in-medium effects. We show, via numerical studies of effective interactions for the sd and the pf shells, that the tensor-force contribution to the monopole term of the effective interaction is barely changed by these renormalization procedures, resulting in almost the same monopole term as the one of the bare NN interactions. We propose to call this feature renormalization persistency of the tensor force, as it is a remarkable property of the renormalization and should have many interesting consequences in nuclear systems. For higher multipole terms, this feature is maintained to a somewhat smaller extent. We present general intuitive explanations for the renormalization persistency of the tensor force as well as analyses of core-polarization terms in perturbation theory. The central force does not exhibit a similar renormalization persistency.status: publishe