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Nuclear Theory·nucl-th

Friday·June 1, 2018

8 papers—4 primary·4 cross-listed

All8Primary4Cross-lists4
  1. 01

    [Submitted on 30 May 2018]

    Bose-Einstein condensation of alpha clusters and new soft mode in 12C--52Fe 4N nuclei in field theoretical superfluid cluster model

    R. Katsuragi · Y. Kazama · J. Takahashi · Y. Nakamura · Y. Yamanaka · S. Ohkubo

    Bose-Einstein condensation of alpha clusters in light and medium-heavy nuclei is studied in the frame of the field theoretical superfluid cluster model. The order parameter of the phase transition from the Wigner phase to the Nambu-Goldstone phase is a superfluid amplitude, square of the moduli of which is the superfluid density distribution. The zero mode operators due to the spontaneous symmetry breaking of the global phase in the finite number of alpha clusters are rigorously treated. The theory is systematically applied to N alpha nuclei from12C-52Fe at various condensation rates. In 12C it is found that the energy levels of the gas-like well-developed alpha cluster states above the Hoyle state are reproduced well in agreement with experiment for realistic condensation rates of alpha clusters. The electric E2 and E0 transitions are calculated and found to be sensitive to the condensation rates. The profound raison d'etre of the alpha cluster gas-like states above the Hoyle state, whose structure has been interpreted geometrically in the nuclear models without the order parameter such as the cluster models or ab initio calculations, is revealed. It is found that in addition to the Bogoliubov-de Gennes vibrational mode states collective states of the zero mode operators appear systematically at low excitation energies from the N alpha threshold energy. These collective states, new-type soft modes in nuclei due to the Bose-Einstein condensation of the alpha clusters, emerge systematically in light and medium-heavy mass regions and are also located at high excitation energies from the ground state in contrast to the traditional concept of soft mode in the low excitation energy region.

    Comments:
    19 pages. 22 figures
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1805.12255 [pdf]
    PRC(2018)·18 citations
  2. 02

    [Submitted on 30 May 2018]

    First-forbidden transitions in the reactor anomaly

    L. Hayen🇧🇪 · J. Kostensalo🇫🇮 · N. Severijns🇧🇪 · J. Suhonen🇫🇮

    We study the dominant forbidden transitions in the antineutrino spectra of the fission actinides from 4 MeV onward using the nuclear shell model. Through explicit calculation of the shape factor, taking into account Coulomb corrections, we show the expected changes on cumulative electron and antineutrino spectra. Compared to the usual allowed approximation this results in a minor decrease of electron spectra from 4 MeV and onward, whereas an increase of several percent is observed in antineutrino spectra. We show that, despite their limited number, forbidden transitions dominate the spectral flux for most of the experimentally accessible range. Based on the shell model calculations we attempt a parametrization of forbidden transitions and propose a spectral correction for all forbidden transitions. We enforce correspondence with the ILL dataset using a summation+conversion approach. When compared against modern reactor neutrino experiments, the resultant spectral change is observed to be of comparable magnitude and shape as the reported spectral shoulder, drastically decreasing the statistical significance of the latter.

    Comments:
    Additional information regarding uncertainty estimation, extension of the final analysis to a summation+conversion approach
    Subjects:
    Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
    arXiv:
    1805.12259 [pdf]
    Phys. Rev. C 100, 054323 (2019)·5 citations
  3. 03

    [Submitted on 31 May 2018]

    Analytical and numerical analysis of the complete Lipkin-Meshkov-Glick Hamiltonian

    Giampaolo Co' · Stefano De Leo

    The Lipkin-Meshkov-Glick is a simple, but not trivial, model of a quantum many-body system which allows us to solve the many-body Schrödinger equation without making any approximation. The model, which in its unperturbed case is composed only by two energy levels, includes two interacting terms. A first one, the interaction, which promotes or degrade pairs of particles, and a second one, the interaction, which scatters one particle in the upper and another in the lower energy level. In comparing this model with other approximation methods, the term interaction is often set to zero. In this paper, we show how the presence of this interaction changes the global structure of the system, generates degeneracies between the various eigenstates and modifies the energy eigenvalues structure. We present analytical solutions for systems of two and three particles and, for some specific cases, also for four, six and eight particles. The solutions for systems with more than eight particles are only numerical but their behaviour can be well understood by considering the extrapolations of the analytical results. Of particular interest it is the study of how the interaction affects the energy gap between the ground state and the first-excited state.

    Comments:
    17 pages, 8 figures
    Subjects:
    Nuclear Theory (nucl-th); Quantum Physics (quant-ph)
    arXiv:
    1805.12442 [pdf]
    IJMPE(2018)·10 citations
  4. 04

    [Submitted on 30 May 2018]

    - interaction from the reaction near threshold

    Ju-Jun Xie🇨🇳 · Wei-Hong Liang🇨🇳 · Eulogio Oset🇪🇸

    We analyze the data on the total cross sections for the reaction close to threshold and look for possible bound states. We develop a framework in which the optical potential is the key ingredient, rather than parameterizing the scattering matrix, as is usually done. The strength of this potential, together with some production parameters, are fitted to the available experimental data. The relationship of the scattering matrix to the optical potential is established using the Bethe-Salpeter equation and the loop function incorporates the range of the interaction given by the experimental density. However, when we look for poles of the scattering matrix, we get poles in the bound region, poles in the positive energy region or no poles at all. If we further restrict the results with constraints from a theoretical model with all its uncertainties the bound states are not allowed. However, we find a bump structure in of the amplitude below threshold for the remaining solutions.

    Comments:
    More calculations and discussions added. arXiv admin note: substantial text overlap with arXiv:1609.03399
    Subjects:
    Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
    arXiv:
    1805.12532 [pdf]
    EPJA(2019)·15 citations

Affiliations

first authorsco-authorsvia INSPIRE