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Nuclear Theory·nucl-th

Friday·February 5, 2021

10 papers—6 primary·4 cross-listed

All10Primary6Cross-lists4
  1. 01

    [Submitted on 3 Feb 2021]

    Th isomer from a nuclear model perspective

    Nikolay Minkov🇧🇬 · Adriana Pálffy🇩🇪

    The physical conditions for the emergence of the extremely low-lying nuclear isomer Th at approximately 8 eV are investigated in the framework of our recently proposed nuclear structure model. Our theoretical approach explains the Th-isomer phenomenon as the result of a very fine interplay between collective quadrupole-octupole and single-particle dynamics in the nucleus. We find that the isomeric state can only appear in a rather limited model space of quadrupole-octupole deformations in the single-particle potential, with the octupole deformation being of a crucial importance for its formation. Within this deformation space the model-described quantities exhibit a rather smooth behaviour close to the line of isomer-ground state quasi-degeneracy determined by the crossing of the corresponding single-particle orbitals. Our comprehensive analysis confirms the previous model predictions for reduced transition probabilities and the isomer magnetic moment, while showing a possibility for limited variation in the ground-state magnetic moment theoretical value. These findings prove the reliability of the model and suggest that the same dynamical mechanism could manifest in other actinide nuclei giving a general prescription for the search and exploration of similar isomer phenomena.

    Comments:
    22 pages, 14 figures
    Subjects:
    Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
    arXiv:
    2102.02288 [pdf]
    PRC(2021)·30 citations
  2. 02

    [Submitted on 3 Feb 2021]

    Two- and three-nucleon contact interactions and ground-state energies of light- and medium-mass nuclei

    R. Schiavilla · L. Girlanda · A. Gnech · A. Kievsky · A. Lovato · L.E. Marcucci · M. Piarulli · M. Viviani

    Classes of two-nucleon () contact interactions are developed in configuration space at leading order (LO), next-to-leading order (NLO), and next-to-next-to-next-to-leading order (N3LO) by fitting the experimental singlet scattering length and deuteron binding energy at LO, and and scattering data in the laboratory-energy range 0--15 MeV at NLO and 0--25 MeV at N3LO. These interactions are regularized by including two Gaussian cutoffs, one for = and the other for = channels. The cutoffs are taken to vary in the ranges =--2.3) fm and =--3.0) fm. The 780 (1,100) data points up to 15 (25) MeV energy, primarily differential cross sections, are fitted by the NLO (N3LO) models with a /datum about 1.7 or less (well below 1.5), when harder cutoff values are adopted. As a first application, we report results for the binding energies of nuclei with mass numbers =--6 and 16 obtained with selected LO and NLO models both by themselves as well as in combination with a LO three-nucleon () contact interaction. The latter is characterized by a single low-energy constant that is fixed to reproduce the experimental H binding energy. The inclusion of the interaction largely removes the sensitivity to cutoff variations in the few-nucleon systems and leads to predictions for the He and He binding energies that cluster around 7.8 MeV and 30 MeV, respectively. However, in O this cutoff sensitivity remains rather strong. Finally, predictions at LO only are also reported for medium-mass nuclei with =, 48, and 90.

    Comments:
    23 pages, 6 figures
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    2102.02327 [pdf]
    PRC(2021)·41 citations
  3. 03

    [Submitted on 4 Feb 2021]

    Microscopic Calculation of Fission Product Yields with Particle Number Projection

    Marc Verriere🇺🇸 · David Regnier🇺🇸 · Nicolas Schunck🇫🇷

    Fission fragments' charge and mass distribution is an important input to applications ranging from basic science to energy production or nuclear non-proliferation. In simulations of nucleosynthesis or calculations of superheavy elements, these quantities must be computed from models, as they are needed in nuclei where no experimental information is available. Until now, standard techniques to estimate these distributions were not capable of accounting for fine-structure effects, such as the odd-even staggering of the charge distributions. In this work, we combine a fully-microscopic collective model of fission dynamics with a recent extension of the particle number projection formalism to provide the highest-fidelity prediction of the primary fission fragment distributions for the neutron-induced fission of U and Pu. We show that particle number projection is an essential ingredient to reproduce odd-even staggering in the charge yields and benchmark the performance of various empirical probability laws that could simulate its effect. This new approach also enables for the first time the realistic determination of two-dimensional isotopic yields within nuclear density functional theory.

    Comments:
    15 pages, 11 figures
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    2102.02346 [pdf]
    PRC(2021)·40 citations
  4. 04

    [Submitted on 4 Feb 2021]

    Entrainment effects in neutron-proton mixtures within the nuclear-energy density functional theory. I. Low-temperature limit

    Nicolas Chamel · Valentin Allard

    Mutual entrainment effects in cold neutron-proton mixtures are studied in the framework of the self-consistent nuclear energy-density functional theory. Exact expressions for the mass currents, valid for both homogeneous and inhomogeneous systems, are directly derived from the time-dependent Hartree-Fock equations with no further approximation. The equivalence with the Fermi-liquid expression is also demonstrated. Focusing on neutron-star cores, a convenient and simple analytical formulation of the entrainment matrix in terms of the isovector effective mass is found, thus allowing to relate entrainment phenomena in neutron stars to isovector giant dipole resonances in finite nuclei. Results obtained with different functionals are presented. These include the Brussels-Montreal functionals, for which unified equations of state of neutron stars have been recently calculated.

    Comments:
    21 pages, 2 figures
    Subjects:
    Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE)
    arXiv:
    2102.02474 [pdf]
    PRC(2019)·17 citations
  5. 05

    [Submitted on 4 Feb 2021]

    Selfinteracting Particle-Antiparticle System of Bosons

    D. Anchishkin🇺🇦 · V. Gnatovskyy🇺🇦 · D. Zhuravel🇺🇦 · V. Karpenko🇺🇦

    Thermodynamic properties of a system of interacting boson particles and antiparticles at finite temperatures are studied within the framework of the thermodynamically consistent Skyrme-like mean-field model. The mean field contains both attractive and repulsive terms. Self-consistency relations between the mean field and thermodynamic functions are derived. We assume conservation of the isospin density for all temperatures. It is shown that, independently of the strength of the attractive mean field, at the critical temperature the system undergoes the phase transition of second-order to the Bose-Einstein condensate, which exists in the temperature interval . We obtained that the condensation represents a discontinuity of the derivative of the heat capacity at , and condensate occurs only for the component with a higher particle-number density in the particle-antiparticle system.

    Comments:
    20 pages, 9 figures, LaTeX; Several typos have been corrected in the text. We have added a comparison of some of the obtained thermodynamic quantities with analog quantities for an ideal gas
    Subjects:
    Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Quantum Physics (quant-ph)
    arXiv:
    2102.02529 [pdf]
    PRC(2022)·6 citations
  6. 06

    [Submitted on 4 Feb 2021]

    Normalizing flows for microscopic many-body calculations: an application to the nuclear equation of state

    Jack Brady · Pengsheng Wen · Jeremy W. Holt

    Normalizing flows are a class of machine learning models used to construct a complex distribution through a bijective mapping of a simple base distribution. We demonstrate that normalizing flows are particularly well suited as a Monte Carlo integration framework for quantum many-body calculations that require the repeated evaluation of high-dimensional integrals across smoothly varying integrands and integration regions. As an example, we consider the finite-temperature nuclear equation of state. An important advantage of normalizing flows is the ability to build highly expressive models of the target integrand, which we demonstrate enables precise evaluations of the nuclear free energy and its derivatives. Furthermore, we show that a normalizing flow model trained on one target integrand can be used to efficiently calculate related integrals when the temperature, density, or nuclear force is varied. This work will support future efforts to build microscopic equations of state for numerical simulations of supernovae and neutron star mergers that employ state-of-the-art nuclear forces and many-body methods.

    Comments:
    6 pages, 4 figures, accepted to Physical Review Letters
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    2102.02726 [pdf]
    PRL(2021)·10 citations

Affiliations

first authorsco-authorsvia INSPIRE