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Nuclear Theory·nucl-th

Monday·February 20, 2017

7 papers—3 primary·4 cross-listed

All7Primary3Cross-lists4
  1. 01

    [Submitted on 16 Feb 2017]

    Ab initio calculations of the isotopic dependence of nuclear clustering

    Serdar Elhatisari🇩🇪 · Evgeny Epelbaum🇺🇸 · Hermann Krebs🇺🇸 · Timo A. Lähde🇩🇪 · Dean Lee🇺🇸 · Ning Li🇩🇪 · Bing-nan Lu🇩🇪 · Ulf-G. Meißner🇩🇪 · Gautam Rupak🇺🇸

    Nuclear clustering describes the appearance of structures resembling smaller nuclei such as alpha particles (4He nuclei) within the interior of a larger nucleus. While clustering is important for several well-known examples, much remains to be discovered about the general nature of clustering in nuclei. In this letter we present lattice Monte Carlo calculations based on chiral effective field theory for the ground states of helium, beryllium, carbon, and oxygen isotopes. By computing model-independent measures that probe three- and four-nucleon correlations at short distances, we determine the shape of the alpha clusters and the entanglement of nucleons comprising each alpha cluster with the outside medium. We also introduce a new computational approach called the pinhole algorithm, which solves a long-standing deficiency of auxiliary-field Monte Carlo simulations in computing density correlations relative to the center of mass. We use the pinhole algorithm to determine the proton and neutron density distributions and the geometry of cluster correlations in 12C, 14C, and 16C. The structural similarities among the carbon isotopes suggest that 14C and 16C have excitations analogous to the well-known Hoyle state resonance in 12C.

    Comments:
    Version to appear in Physical Review Letters. 5 + 12 pages (main + supplemental materials), 3 + 12 figures (main + supplemental materials)
    Subjects:
    Nuclear Theory (nucl-th); Solar and Stellar Astrophysics (astro-ph.SR); High Energy Physics — Lattice (hep-lat); Nuclear Experiment (nucl-ex)
    arXiv:
    1702.05177 [pdf]
    PRL(2017)·106 citations
  2. 02

    [Submitted on 17 Feb 2017]

    Neutron-proton scattering at next-to-next-to-leading order in Nuclear Lattice Effective Field Theory

    Jose Manuel Alarcón🇩🇪 · Dechuan Du🇩🇪 · Nico Klein🇩🇪 · Timo A. Lähde🇩🇪 · Dean Lee🇺🇸 · Ning Li🇩🇪 · Bing-Nan Lu🇩🇪 · Thomas Luu🇩🇪 · Ulf-G. Meißner🇩🇪

    We present a systematic study of neutron-proton scattering in Nuclear Lattice Effective Field Theory (NLEFT), in terms of the computationally efficient radial Hamiltonian method. Our leading-order (LO) interaction consists of smeared, local contact terms and static one-pion exchange. We show results for a fully non-perturbative analysis up to next-to-next-to-leading order (NNLO), followed by a perturbative treatment of contributions beyond LO. The latter analysis anticipates practical Monte Carlo simulations of heavier nuclei. We explore how our results depend on the lattice spacing a, and estimate sources of uncertainty in the determination of the low-energy constants of the next-to-leading-order (NLO) two-nucleon force. We give results for lattice spacings ranging from a = 1.97 fm down to a = 0.98 fm, and discuss the effects of lattice artifacts on the scattering observables. At a = 0.98 fm, lattice artifacts appear small, and our NNLO results agree well with the Nijmegen partial-wave analysis for S-wave and P-wave channels. We expect the peripheral partial waves to be equally well described once the lattice momenta in the pion-nucleon coupling are taken to coincide with the continuum dispersion relation, and higher-order (N3LO) contributions are included. We stress that for center-of-mass momenta below 100 MeV, the physics of the two-nucleon system is independent of the lattice spacing.

    Comments:
    22 pages, 8 figures
    Subjects:
    Nuclear Theory (nucl-th); High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph)
    arXiv:
    1702.05319 [pdf]
    EPJA(2017)·30 citations
  3. 03

    [Submitted on 17 Feb 2017]

    Nuclear equation of state for core-collapse supernova simulations with realistic nuclear forces

    H. Togashi · K. Nakazato · Y. Takehara · S. Yamamuro · H. Suzuki · M. Takano

    A new table of the nuclear equation of state (EOS) based on realistic nuclear potentials is constructed for core-collapse supernova numerical simulations. Adopting the EOS of uniform nuclear matter constructed by two of the present authors with the cluster variational method starting from the Argonne v18 and Urbana IX nuclear potentials, the Thomas-Fermi calculation is performed to obtain the minimized free energy of a Wigner-Seitz cell in non-uniform nuclear matter. As a preparation for the Thomas-Fermi calculation, the EOS of uniform nuclear matter is modified so as to remove the effects of deuteron cluster formation in uniform matter at low densities. Mixing of alpha particles is also taken into account following the procedure used by Shen et al. (1998, 2011). The critical densities with respect to the phase transition from non-uniform to uniform phase with the present EOS are slightly higher than those with the Shen EOS at small proton fractions. The critical temperature with respect to the liquid-gas phase transition decreases with the proton fraction in a more gradual manner than in the Shen EOS. Furthermore, the mass and proton numbers of nuclides appearing in non-uniform nuclear matter with small proton fractions are larger than those of the Shen EOS. These results are consequences of the fact that the density derivative coefficient of the symmetry energy of our EOS is smaller than that of the Shen EOS.

    Comments:
    40 pages, 15 figures, typos corrected, final version published in Nuclear Physics A. The EOS table constructed in this study is available on the Web at http://www.np.phys.waseda.ac.jp/EOS/
    Subjects:
    Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE)
    arXiv:
    1702.05324 [pdf]
    NPA(2017)·223 citations

Affiliations

first authorsco-authorsvia INSPIRE