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Nuclear Theory·nucl-th

Thursday·January 24, 2019

9 papers—5 primary·4 cross-listed

All9Primary5Cross-lists4
  1. 01

    [Submitted on 22 Jan 2019]

    Coupling between superfluid neutrons and superfluid protons in the elementary excitations of neutron star matter

    M. Baldo🇮🇹 · C. Ducoin🇫🇷

    Several phenomena occurring in neutron stars are affected by the elementary excitations that characterize the stellar matter. In particular, low-energy excitations can play a major role in the emission and propagation of neutrinos, neutron star cooling and transport processes. In this paper, we consider the elementary modes in the star region where both proton and neutron components are superfluid. We study the overall spectral functions of protons, neutrons and electrons on the basis of the Coulomb and nuclear interactions. This study is performed in the framework of the Random Phase Approximation, generalized to superfluid systems. The formalism we use ensures that the Generalized Ward's Identities are satisfied. We focus on the coupling between neutrons and protons. On one hand this coupling results in collective modes that involve simultaneously neutrons and protons, on the other hand it produces a damping of the excitations. Both effects are especially visible in the spectral functions of the different components of the matter. At high density while the neutrons and protons tend to develop independent excitations, as indicated by the spectral functions, the neutron-proton coupling still produces a strong damping of the modes.

    Comments:
    9 pages 6 figures, accepted in Physical Review C. arXiv admin note: substantial text overlap with arXiv:1708.03794
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1901.07550 [pdf]
    PRC(2019)·3 citations
  2. 02

    [Submitted on 22 Jan 2019]

    Neutron drip line in the Ca region from Bayesian model averaging

    Léo Neufcourt · Yuchen Cao · Witold Nazarewicz · Erik Olsen · Frederi Viens

    The region of heavy calcium isotopes forms the frontier of experimental and theoretical nuclear structure research where the basic concepts of nuclear physics are put to stringent test. The recent discovery of the extremely neutron-rich nuclei around Ca [Tarasov, 2018] and the experimental determination of masses for Ca (Michimasa, 2018] provide unique information about the binding energy surface in this region. To assess the impact of these experimental discoveries on the nuclear landscape's extent, we use global mass models and statistical machine learning to make predictions, with quantified levels of certainty, for bound nuclides between Si and Ti. Using a Bayesian model averaging analysis based on Gaussian-process-based extrapolations we introduce the posterior probability for each nucleus to be bound to neutron emission. We find that extrapolations for drip-line locations, at which the nuclear binding ends, are consistent across the global mass models used, in spite of significant variations between their raw predictions. In particular, considering the current experimental information and current global mass models, we predict that Ca has an average posterior probability % to be bound to two-neutron emission while the nucleus Ca is likely to decay by emitting a neutron ( %).

    Comments:
    Supplementary Material available upon request
    Subjects:
    Nuclear Theory (nucl-th); Machine Learning (stat.ML)
    arXiv:
    1901.07632 [pdf]
    PRL(2019)·148 citations
  3. 03

    [Submitted on 23 Jan 2019]

    The critical notes to the solutions of the "puzzle" of hyperfine structure in 82+ and 80+ Bi ions

    F. F. Karpeshin · M. B. Trzhaskovskaya

    Some aspects of description of the Bohr-Weisskopf effect in hyperfine splitting of the H- and Li-like ions of 209Bi are considered by application of the surface and volume models of the nuclear currents. Extension of these models, used in internal conversion theory, to description of the HFS allows one to successfully describe the effect, without resorting to the specific differences. The latters are shown not to be needed at all. Moreover, they turn out to depend on the nuclear model even stronger than the HFS values themselves. Comparison of the calculated HFS values to experiment shows a satisfactory agreement. Both models provide equally good description of the effect. However, they result in different values of the retrieved rms radius of the nuclear magnetization. In this respect, situation resembles the proton radius puzzle. Prospects of future research are discussed.

    Comments:
    The content of the paper was presented at the 27th ANNUAL INTERNATIONAL LASER PHYSICS WORKSHOP (Nottingham, July 16-20, 2018), and on the PNPI theoretical devision seminar
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1901.07826 [pdf]
    PRC(2019)·4 citations
  4. 04

    [Submitted on 23 Jan 2019]

    The algebraic molecular model in C and its application to the +C scattering: from densities and transition densities to optical potentials and nuclear formfactors

    A. Vitturi · J. Casal · L. Fortunato · E. G. Lanza

    The algebraic molecular model is used in C to construct densities and transition densities connecting low-lying states of the rotovibrational spectrum, first and foremost those belonging to the rotational bands based on the ground and the Hoyle states. These densities are then used as basic ingredients to calculate, besides electromagnetic transition probabilities, nuclear potentials and formfactors to describe elastic and inelastic +C scattering processes. The calculated densities and transition densities are also compared with those obtained by directly solving the problem of three interacting alpha's within a three-body approach where continuum effects, relevant in particular for the Hoyle state, are properly taken into account.

    Comments:
    Contribution to "Symmetries and Order: Algebraic Methods in Many Body Systems", in honor of F. Iachello
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1901.07954 [pdf]
    AIP Conf.Proc.(2019)·3 citations
  5. 05

    [Submitted on 23 Jan 2019]

    Electron versus muon neutrino induced cross sections in charged current quasi-elastic processes

    Alexis Nikolakopoulos🇧🇪 · Natalie Jachowicz🇧🇪 · Nils Van Dessel🇧🇪 · Kajetan Niewczas🇧🇪 · Raúl González-Jiménez🇪🇸 · José Manuel Udías🇪🇸 · Vishvas Pandey🇺🇸

    Differences between and quasielastic cross sections are essential in neutrino oscillation analyses and CP violation searches for experiments such as DUNE and T2HK. The ratio of these is however poorly known experimentally and for certain kinematic regions theoretical models give contradictory answers. We use two independent mean-field based models to investigate this ratio using Ar and C targets. We demonstrate that a proper treatment of the final nucleon's wave function confirms the dominance of over induced cross sections at forward lepton scattering.

    Comments:
    Updated Fig. 2, minor changes to text, accepted for publication in Phys. Rev. Letters
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1901.08050 [pdf]
    PRL(2019)·51 citations

Affiliations

first authorsco-authorsvia INSPIRE