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Nuclear Theory·nucl-th

Thursday·June 21, 2018

8 papers—4 primary·4 cross-listed

All8Primary4Cross-lists4
  1. 01

    [Submitted on 19 Jun 2018]

    Shell-model coupled-cluster method for open-shell nuclei

    Z. H. Sun · T. D. Morris · G. Hagen · G. R. Jansen · T. Papenbrock

    We present an approach to derive effective shell-model interactions from microscopic nuclear forces. The similarity-transformed coupled-cluster Hamiltonian decouples the single-reference state of a closed-shell nucleus and provides us with a core for the shell model. We use a second similarity transformation to decouple a shell-model space from the excluded space. We show that the three-body terms induced by both similarity transformations are crucial for an accurate computation of ground and excited states. As a proof of principle we use a nucleon-nucleon interaction from chiral effective field theory, employ a He core, and compute low-lying states of He and Li in -shell model spaces. Our results agree with benchmarks from full configuration interaction.

    Comments:
    12 pages, 16 figures
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1806.07405 [pdf]
    PRC(2018)·50 citations
  2. 02

    [Submitted on 20 Jun 2018]

    Analytical description of the excited state phase transition to octupole deformed shape in alternating parity bands

    E.V. Mardyban · T.M. Shneidman · E.A. Kolganova · R.V. Jolos · S.-G. Zhou

    Angular momentum dependences of the parity splitting and electric dipole transitions in the alternating parity bands of heavy nuclei have been analyzed. It is shown that these dependences can be treated in a universal way with a single parameter of critical angular momentum, which characterizes phase transition from octupole vibrations to the stable octupole deformation. Using the simple but useful model of axially-symmetric reflection-asymmetric mode, the analytical expression for the parity splitting and electric dipole transitional moment have been obtained. The results obtained are in a good agreement with the experimental data for various isotopes of Ra, Th, U, and Pu.

    Comments:
    11 pages, 7 figures
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1806.07548 [pdf]
    CPC(2018)·7 citations
  3. 03

    [Submitted on 20 Jun 2018]

    Effects of mixing in the decay of hypernuclei

    Jordi Maneu Victoria🇪🇸 · Assumpta Parreño🇪🇸 · Àngels Ramos🇪🇸

    We study the non-mesonic weak decay of the doubly-strange hypernucleus He within a model which considers the exchange of pseudoscalar and vector mesons. Special attention is paid into quantifying the strong interaction effects, focussing on the interaction among the two {\Lambda} hyperons which induces novel weak transitions, whereby {\Lambda}{\Lambda}, {\Xi}N and {\Sigma}{\Sigma} states decay into a hyperon-nucleon pair. The initial strangeness -2 wave function is obtained from the solution of a G-matrix equation with the input of realistic strong baryon-baryon potentials, while the final hyperon-nucleon wave functions are derived analogously from a microscopic T-matrix calculation. The new {\Lambda}{\Lambda} Y N decay rate studied in this work, , represents 3-4% of the total one-baryon induced non-mesonic decay and is remarkably affected by strong interaction effects. In particular, the relative importance of the partial decay rates, encoded in the ratio , gets inverted when the mixing to {\Xi}N states is incorporated in the initial correlated {\Lambda}{\Lambda} wave function. This sensitivity can be used experimentally to learn about the strong interaction in the strangeness -2 sector.

    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1806.07666 [pdf]
    PRC(2018)·1 citation
  4. 04

    [Submitted on 20 Jun 2018]

    A systematic study of giant quadrupole resonances with the subtracted second random--phase approximation: beyond--mean--field centroids and fragmentation

    Olivier Vasseur🇫🇷 · Danilo Gambacurta🇷🇴 · Marcella Grasso🇫🇷

    A systematic analysis of giant quadrupole resonances is performed for several nuclei, from Si to Pb, within the subtracted second random--phase--approximation (SSRPA) model in the framework of the energy--density--functional theory. Centroid energies and widths of the isoscalar giant quadrupole resonances are compared with the corresponding random--phase--approximation (RPA) values. We find lower SSRPA centroid energies compared to the RPA values leading, in general, to a better agreement with the experimental data. As far as the widths are concerned, we observe for both SSRPA and RPA cases a global attenuation of the single--particle Landau damping going from lighter to heavier nuclei and we obtain, systematically, larger widths in the SSRPA model compared to the RPA case. For some selected nuclei for which high--resolution () experimental data are available, namely Ca, Zr, Sn, and Pb, the theoretical strength distributions are directly compared with the experimental spectra. We observe a significant improvement, with respect to RPA results, in the description of the spreading widths and of the fragmentation of the obtained spectra, due to the coupling between 1 particle-1 hole and 2 particle-2 hole configurations.

    Comments:
    7 figures
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1806.07807 [pdf]
    PRC(2018)·12 citations

Affiliations

first authorsco-authorsvia INSPIRE