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Nuclear Theory·nucl-th

Wednesday·October 4, 2023

14 papers—6 primary·8 cross-listed

All14Primary6Cross-lists8
  1. 01

    [Submitted on 2 Oct 2023]

    Auxiliary Field Quantum Monte Carlo for Dilute Neutrons on the Lattice

    Ryan Curry🇨🇦 · Jayani Dissanayake🇨🇦 · Stefano Gandolfi🇺🇸 · Alexandros Gezerlis🇨🇦

    We employ constrained path Auxiliary Field Quantum Monte Carlo (AFQMC) in the pursuit of studying physical nuclear systems using a lattice formalism. Since AFQMC has been widely used in the study of condensed-matter systems such as the Hubbard model, we benchmark our method against published results for both one- and two-dimensional Hubbard model calculations. We then turn our attention to cold-atomic and nuclear systems. We use an onsite contact interaction that can be tuned in order to reproduce the known scattering length and effective range of a given interaction. Developing this machinery allows us to extend our calculations to study nuclear systems within a lattice formalism. We perform initial calculations for a range of nuclear systems from two- to few-body neutron systems.

    Comments:
    14 pages, 6 figures, 2 tables
    Subjects:
    Nuclear Theory (nucl-th); Quantum Gases (cond-mat.quant-gas); Computational Physics (physics.comp-ph)
    arXiv:
    2310.01504 [pdf]
    Phil.Trans.A.Math.Phys.Eng.Sci.(2024)·6 citations
  2. 02

    [Submitted on 2 Oct 2023]

    Neural Network Emulation of Spontaneous Fission

    Daniel Lay · Eric Flynn · Samuel A. Giuliani · Witold Nazarewicz · Leó Neufcourt

    Large-scale computations of fission properties are an important ingredient for nuclear reaction network calculations simulating rapid neutron-capture process (the r process) nucleosynthesis. Due to the large number of fissioning nuclei contributing to the r process, a microscopic description of fission based on nuclear density functional theory (DFT) is computationally challenging. We explore the use of neural networks (NNs) to construct DFT emulators capable of predicting potential energy surfaces and collective inertia tensors across the whole nuclear chart. We use constrained Hartree-Fock-Boguliubov (HFB) calculations to predict the potential energy and collective inertia tensor in the axial quadrupole and octupole collective coordinates, for a set of nuclei in the r-process region. We then employ NNs to emulate the HFB energy and collective inertia tensor across the considered region of the nuclear chart. Least-action pathways characterizing spontaneous fission half-lives and fragment yields are obtained using the nudged elastic band method. The potential energy predicted by NNs agrees with the DFT value to within a root-mean-square error of 500 keV, and the collective inertia components agree to within an order of magnitude. The exit points on the outer turning line are found to be well emulated. For the spontaneous fission half-lives the NN emulation provides values that are found to agree with the DFT predictions within a factor of across more than 70 orders of magnitude. Neural networks are able to emulate the potential energy and collective inertia well enough to reasonably predict physical observables. Future directions of study, such as the inclusion of additional collective degrees of freedom and active learning, will improve the predictive power of microscopic theory and further enable large-scale fission studies.

    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    2310.01608 [pdf]
    PRC(2024)·21 citations
  3. 03

    [Submitted on 3 Oct 2023]

    Relativistic magnetohydrodynamics of a spinful and vortical fluid: Entropy current analysis

    M. Kiamari🇮🇷 · N. Sadooghi🇮🇷 · M. Sedighi Jafari🇮🇷

    We generalize a recently introduced formulation of relativistic spinful and vortical fluid to relativistic magnetohydrodynamics (MHD). We refer to it as the "Spinful-Vortical MHD" (SVMHD). The aim is to scrutinize the interplay between the vorticity, magnetic field, and spin, which is treated as a quantum object, in contrast to other formulations of spin hydrodynamics. To this purpose, we first perform a standard entropy current analysis up to first-order gradient expansion, as well as , where is the Planck constant. In contrast to alternative formulations of spin MHD, in the absence of vorticity, the zeroth-order energy-momentum tensor includes an additional magneto-vorticity mixed term and reduces, as expected, to the energy-momentum tensor of MHD. We show that in the first-order of gradient expansion, dissipative transport coefficients appear. They satisfy certain constraints that guarantee the positive definiteness of the entropy production rate. We then modify the formulation of SVMHD by replacing the magnetic part of the thermal vorticity tensor with its electric part. Carrying out the same analysis as in the standard formulation, we show that in this case, the first-order constitutive relations consist of nondissipative Hall-like coefficients, apart from dissipative coefficients. This difference arises from different behavior of the electric and magnetic part of the thermal vorticity under time-reversal transformation.

    Comments:
    13 pages
    Subjects:
    Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
    arXiv:
    2310.01874 [pdf]
    PRD(2024)·22 citations
  4. 04

    [Submitted on 3 Oct 2023]

    The hyperon superfluidity and the hyperon couplings in neutron stars within the relativistic mean field model

    Zhong-Hao Tu🇨🇳 · Shan-Gui Zhou🇨🇳

    A systematic study of the effects of hyperon couplings on hyperon superfluidity is conducted by using the relativistic mean field model. Combining the slope of symmetry energy, the hyperon couplings are determined in two ways -- by the hypernuclear potentials or under the SU(3) symmetry. In either way, the hyperon coupling constants cannot be fixed uniquely but vary within a certain range due to the uncertainties in hypernuclear potentials or the breaking of SU(6) to SU(3) symmetry. When the coupling constants are constrained by the hypernuclear potentials, the pairings of and are strong and they each show little variations. The pairing of is more sensitive to hyperon potentials and the slope of symmetry energy. Under the SU(3) symmetry, the superfluidity of various hyperons differ significantly. The dependence of the pairings of and on the additional parameters of SU(3) symmetry are the opposite to that of the maximum mass of neutron stars on the additional parameters of SU(3) symmetry, while the pairing of shows a similar trend in general. These results suggest that the hyperon superfluidity associated with astrophysical processes is an essential window to probe the physics of neutron star cores, the hyperon-hyperon interactions and the SU(3) symmetry. Compared with other hyperons, could serve as a cleaner glass for this purpose.

    Comments:
    9 pages, 5 figures
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    2310.01922 [pdf]
    0 citations
  5. 05

    [Submitted on 3 Oct 2023]

    Nuclear models for inclusive lepton-nucleus scattering in the quasi-elastic region and beyond

    Valerio Belocchi🇮🇹 · Maria Benedetta Barbaro🇮🇹 · Arturo De Pace🇮🇹 · Marco Martini🇫🇷

    High-precision measurements in neutrino oscillation experiments require a very accurate description of the lepton-nucleus scattering process. Several cross-section calculations are available, but important discrepancies are still present between different model predictions. For the quasi-elastic channel, dominated by one particle-one hole excitations, an overview over several nuclear models - specifically Relativistic Fermi Gas, SuperScaling Approach, Spectral Function, Hartree-Fock and Random Phase Approximation - is presented and compared with data for electron-nucleus scattering, a very important process for testing theoretical models validity, highlighting the specific features of each approach. Furthermore an ongoing microscopic calculation of the two particle-two hole excitations contribution to the electromagnetic response is presented, and some preliminary results are shown.

    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    2310.02007 [pdf]
    Nucl.Theor.(2023)·0 citations
  6. 06

    [Submitted on 3 Oct 2023]

    Re-evaluation of the Ne(,)Na reaction rate: matrix analysis of the non-resonant capture and effect of the 8945 keV () resonance strength

    Sk Mustak Ali · Rajkumar Santra · Sathi Sharma · Ashok kumar Mondal

    The Ne()Na capture reaction is a key member of the Ne-Na cycle of hydrogen burning. The rate of this reaction is critical in classical novae nucleosynthesis and hot bottom burning processes (HBB) in asymptotic giant branch (AGB) stars. Despite its astrophysical importance, significant uncertainty remains in the reaction rate due to several narrow low energy resonances lying near the Gamow window. The present work revisits this reaction by examining the contribution of the 8664 keV subthreshold state and the 151 keV doublet resonance state of 7/2 configuration in Na. Finite range distorted-wave Born approximation (FRDWBA) analyses of existing Ne(He,)Na transfer reaction data were carried out to extract the peripheral asymptotic normalization coefficients (ANC) of the 8664 keV state. The ANC value obtained in the present work is higher compared to the previous work by Santra et al.~\cite{SA20}. Systematic -matrix calculations were performed to obtain the non-resonant astrophysical -factor utilizing the enhanced ANC value. The resonance strengths of the 8945 keV doublets were deduced from shell model calculations. The total reaction rate is found to be higher at temperatures relevant for the HBB processes, compared to the recent rate measured by Williams et al.~\cite{WI20}, and matches the rate by Williams et al.~\cite{WI20} at temperatures of interest for classical novae nucleosynthesis.

    Subjects:
    Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
    arXiv:
    2310.02099 [pdf]
    0 citations

Affiliations

first authorsco-authorsvia INSPIRE