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Nuclear Theory·nucl-th

Friday·July 14, 2017

11 papers—3 primary·8 cross-listed

All11Primary3Cross-lists8
  1. 01

    [Submitted on 13 Jul 2017]

    Neutrinoless double-beta decay matrix elements in large shell-model spaces with the generator-coordinate method

    C.F. Jiao🇺🇸 · J. Engel🇺🇸 · J.D. Holt🇨🇦

    We use the generator-coordinate method with realistic shell-model interactions to closely approximate full shell-model calculations of the matrix elements for the neutrinoless double-beta decay of Ca, Ge, and Se. We work in one major shell for the first isotope, in the space for the second and third, and finally in two major shells for all three. Our coordinates include not only the usual axial deformation parameter , but also the triaxiality angle and neutron-proton pairing amplitudes. In the smaller model spaces our matrix elements agree well with those of full shell-model diagonalization, suggesting that our Hamiltonian-based GCM captures most of the important valence-space correlations. In two major shells, where exact diagonalization is not currently possible, our matrix elements are only slightly different from those in a single shell.

    Comments:
    8 pages, 7 figures
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1707.03940 [pdf]
    PRC(2017)·64 citations
  2. 02

    [Submitted on 13 Jul 2017]

    Pairing and short-range correlations in nuclear systems

    A. Rios · A. Polls · W. H. Dickhoff

    The structure and density dependence of the pairing gap in infinite matter is relevant for astrophysical phenomena and provides a starting point for the discussion of pairing properties in nuclear structure. Short-range correlations can significantly deplete the available single-particle strength around the Fermi surface and thus provide a reduction mechanism of the pairing gap. Here, we study this effect in the singlet and triplet channels of both neutron matter and symmetric nuclear matter. Our calculations use phase-shift equivalent interactions and chiral two-body and three-body interactions as a starting point. We find an unambiguous reduction of the gap in all channels with very small dependence on the NN force in the singlet neutron matter and the triplet nuclear matter channel. In the latter channel, short range correlations alone provide a 50% reduction of the pairing gap.

    Comments:
    Final version, as published in journal after refereeing
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1707.04140 [pdf]
    J.Low Temp.Phys.(2017)·31 citations
  3. 03

    [Submitted on 13 Jul 2017]

    Effects of cluster-shell competition and BCS-like pairing in C

    H. Matsuno · N. Itagaki

    The antisymmetrized quasi-cluster model (AQCM) was proposed to describe {\alpha}-cluster and -coupling shell models on the same footing. In this model, the cluster-shell transition is characterized by two parameters; representing the distance between {\alpha} clusters and {\alpha} describing the breaking of {\alpha} clusters, and the contribution of the spin-orbit interaction, very important in the -coupling shell model, can be taken into account starting with the {\alpha} cluster model wave function. Not only the closure configurations of the major shells, but also the subclosure configurations of the -coupling shell model can be described starting with the {\alpha}-cluster model wave functions; however, the particle hole excitations of single particles have not been fully established yet. In this study we show that the framework of AQCM can be extended even to the states with the character of single particle excitations. For C, two particle two hole (2p2h) excitations from the subclosure configuration of corresponding to BCS-like pairing are described, and these shell model states are coupled with the three {\alpha} cluster model wave functions. The correlation energy from the optimal configuration can be estimated not only in the cluster part but also in the shell model part. We try to pave the way to establish a generalized description of the nuclear structure.

    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1707.04159 [pdf]
    PTEP(2017)·14 citations

Affiliations

first authorsco-authorsvia INSPIRE