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Nuclear Theory·nucl-th

Thursday·July 6, 2017

6 papers—4 primary·2 cross-listed

All6Primary4Cross-lists2
  1. 01

    [Submitted on 5 Jul 2017]

    Nuclear Structure Features of Gamow-Teller Excitations

    Vladimir Zelevinsky · Naftali Auerbach · Bui Minh Loc

    It is widely accepted that nuclear Gamow-Teller transitions are quenched; shell-model calculations also showed a clear anticorrelation between the Gamow-Teller strength and the transition rate of the collective quadrupole excitation from the ground state. We discuss the physics beyond this observation. It is based on the existence of spin-orbit coupling that is responsible for the non-zero probabilities of Gamow-Teller transitions in self-conjugate nuclei (N = Z). The shell-model calculations in the f p-space demonstrate the effects of the gradual artificial removal of the spin-orbit coupling that influences Gamow-Teller and quadrupole modes in opposite way. The realistic spin-orbit splitting moves the cumulative Gamow-Teller strength up and leads to stronger fragmentation; both trends are discussed in terms of simple symmetry arguments. Along with this process, the Gamow-Teller operator excites, in addition to the main line of L = 0 states, states with L = 2 which should be added, with the interference terms, to account for the total strength.

    Comments:
    16 pages, 8 figures
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1707.01293 [pdf]
    PRC(2017)·10 citations
  2. 02

    [Submitted on 5 Jul 2017]

    Periodic orbit bifurcations and local symmetry restorations in exotic-shape nuclear mean fields

    Ken-ichiro Arita

    The semiclassical origins of the enhancement of shell effects in exotic-shape mean-field potentials are investigated by focusing attention on the roles of the local symmetries associated with the periodic-orbit bifurcations. The deformed shell structures for four types of pure octupole shapes in the nuclear mean-field model having a realistic radial dependence are analyzed. Remarkable shell effects are shown for a large Y32 deformation having tetrahedral symmetry. Much stronger shell effects found in the shape parametrization smoothly connecting the sphere and the tetrahedron are investigated from the view point of the classical-quantum correspondence. The local dynamical symmetries associated with the bridge orbit bifurcations are shown to have significant roles in emergence of the exotic deformed shell structures for certain combinations of the surface diffuseness and the tetrahedral deformation parameters.

    Comments:
    9 pages, 13 figures, talk given at the workshop "Shapes and Symmetries in Nuclei: from Experiment to Theory (SSNET'16)", Gif sur Yvette, France, Nov 7-11, 2016
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1707.01309 [pdf]
    Phys.Scripta(2017)·1 citation
  3. 03

    [Submitted on 5 Jul 2017]

    Hyperons in the pasta phase

    Débora P. Menezes🇧🇷 · Constança Providência🇧🇷

    We have investigated under which conditions hyperons (particularly s and s) can be found in the pasta phase. The larger the density and the temperature and the smaller the electron fraction the higher the probability that these particles appear but always in very small amounts. -hyperons only occur in the gas and in smaller amounts than would occur if matter were homogeneous, never with abundancies above 10. The amount of in the gas is at least two orders of magnitude smaller and can be disregarded in practical calculations.

    Comments:
    6 pages, 10 figures
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1707.01338 [pdf]
    PRC(2017)·11 citations
  4. 04

    [Submitted on 5 Jul 2017]

    Pairing Theory of the Wigner Cusp

    K. Neergård

    Conclusions: (1) Calculations with an RPA correction added to the BCS pairing correction conventionally employed in Nilsson-Strutinskij calculations account well for the variation with A of the pattern of masses near N=Z. (2) The RPA correction is insignificant for reproducing the doubly even masses and hence for the shape of the Wigner cusp. (3) It is important, however, that the macroscopic (liquid drop) symmetry energy be proportional to T(T+1). (4) This form of the macroscopic symmetry energy is understood microscopically, in terms of the RPA, to result from the nuclear superfluidity. (5) The variation of the shape of the Wigner cusp is dominated by shell effects. (6) The RPA correction significally reduces the T=0 binding in doubly odd nuclei, thus reducing the required pair coupling constant.

    Comments:
    Talk at the 36th international workshop on nuclear theory, 25 June - 1 July 2017, Rila Mountains, Bulgaria. To be published in Nuclear Theory
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1707.01474 [pdf]
    Nucl.Theor.(2017)·2 citations

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first authorsco-authorsvia INSPIRE