PaperPanorama
FAQ

Nuclear Theory·nucl-th

Thursday·August 22, 2019

7 papers—5 primary·2 cross-listed

All7Primary5Cross-lists2
  1. 01

    [Submitted on 20 Aug 2019]

    Renormalization of pionless effective field theory in the A-body sector

    Mehdi Drissi🇫🇷 · Thomas Duguet🇫🇷 · Vittorio Soma🇫🇷

    Current models of inter-nucleon interactions are built within the frame of Effective Field Theories (EFTs). Contrary to traditional nuclear potentials, EFT interactions require a renormalization of their parameters in order to derive meaningful estimations of observable. In this paper, a renormalization procedure is designed in connection with many-body approximations applicable to large-A systems and formulated within the frame of many-body perturbation theory. The procedure is shown to generate counterterms that are independent of the targeted A-body sector. As an example, the procedure is applied to the random phase approximation. This work constitutes one step towards the design of a practical EFT for many-body systems.

    Comments:
    14 pages, 7 figures, 2 tables. Contribution to the EPJA topical issue: "The tower of effective (field) theories and the emergence of nuclear phenomena"
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1908.07578 [pdf]
    EPJA(2020)·6 citations
  2. 02

    [Submitted on 21 Aug 2019]

    Variational approach for pair optimization in the nucleon pair approximation

    Y. Lei · H. Jiang · S. Pittel

    We propose a pair-condensate variational approach (PCV) to determine a set of the most important collective pairs in the description of low-lying states in atomic nuclei. Having available the precise details on these key collective pairs -- their spin, parity, and structure -- can be particularly useful in calculations based on the nucleon-pair approximation (NPA), helping to reduce their uncertainties. In trial calculations for the transitional Ba isotopes, our variational approach describes the evolution of quadrupole-deformation properties similar to Hartree-Fock treatments, while at the same time highlighting the softness of Ba. Our approach can conclusively determine which collective pairs are critical for obtaining the lowest possible yrast, quasi-beta, quasi-gamma bands, producing both the level structure of these bands and related B(E2) values in reasonable consistency with experiment. These trial calculations suggest that with our PCV approach the NPA can be meaningfully applied to transitional nuclei with a wide spectrum of shapes. We also show that while neutron negative-parity pairs could in principle have an important impact on backbending in Ba, they are not favored for this nucleus.

    Comments:
    16 pages, 6 figures
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1908.07693 [pdf]
    PRC(2020)·11 citations
  3. 03

    [Submitted on 21 Aug 2019]

    Consistent large-scale shell-model analysis of the two-neutrino and single branchings in and

    Joel Kostensalo🇫🇮 · Jouni Suhonen🇫🇮

    Two-neutrino double-beta-decay matrix elements and single beta-decay branching ratios were calculated for Ca and Zr in the interacting nuclear shell model using large single-particle valence spaces with well-tested two-body Hamiltonians. For Ca the matrix element is obtained, which is 5.5\% smaller than the previously reported value of 0.0539. For Zr this work reports the first large-scale shell-model calculation of the nuclear matrix element, yielding a value with extreme single-state dominance. If the scenario where the first state in Nb is at 694.6 keV turns out to be correct, the matrix element is increased to 0.0854. These matrix elements, combined with the available -decay half-life data, yield effective values of the weak axial coupling which in turn are used to produce in a consistent way the -decay branching ratios of % for Ca and % for Zr. These are larger than obtained in previous studies, implying that the detection of the -decay branches could be possible in dedicated experiments sometime in the (near) future.

    Comments:
    13 pages, 8 figures
    Subjects:
    Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
    arXiv:
    1908.07911 [pdf]
    PLB(2020)·25 citations
  4. 04

    [Submitted on 21 Aug 2019]

    Critical endpoint and universality class of neutron superfluids in neutron stars

    Takeshi Mizushima🇯🇵 · Shigehiro Yasui🇯🇵 · Muneto Nitta🇯🇵

    We study the thermodynamics and critical behavior of neutron superfluids in the inner cores of neutron stars. superfluids offer a rich phase diagram including uniaxial/biaxial nematic phases, the ferromagnetic phase, and the cyclic phase. Using the Bogoliubov-de Gennes (BdG) equation as superfluid Fermi liquid theory, we show that a strong (weak) magnetic field drives the first (second) order transition from the dihedral-two biaxial nematic phase to dihedral-four biaxial nematic phase in low (high) temperatures, and their phase boundaries are divided by the critical endpoint (CEP). We demonstrate that the set of critical exponents at the CEP satisfies the Rushbrooke, Griffiths, and Widom equalities, indicating a new universality class. At the CEP, the superfluid exhibits critical behavior with nontrivial critical exponents, indicating a new universality class. Furthermore, we find that the Ginzburg-Landau (GL) equation up to the 8th-order expansion satisfies three equalities and properly captures the physics of the CEP. This implies that the GL theory can provide a tractable way for understanding critical phenomena which may be realized in the dense core of realistic magnetars.

    Comments:
    15 pages, 5 figures
    Subjects:
    Nuclear Theory (nucl-th); Statistical Mechanics (cond-mat.stat-mech)
    arXiv:
    1908.07944 [pdf]
    PRResearch(2020)·15 citations
  5. 05

    [Submitted on 21 Aug 2019]

    A way forward towards improvement of tensor force in \textit{pf}-shell

    Kanhaiya Jha · Pawan Kumar · Shahariar Sarkar · P.K. Raina · Sezgin Aydin

    In many shell model interactions, the tensor force monopole matrix elements often retain systematic trends originating in the bare tensor force. In this work, however, we note for GX-interactions of \textit{pf}-shell that the seven out of ten T = 1 tensor force monopole matrix elements do not share these systematic. We ameliorate this disparity making use of Yukawa-type tensor force and spin-tensor decomposition. Furthermore, we modify the single-particle energy of orbit and two TBMEs of -orbit,and test the revised interaction from Ca to Ge isotopes with various physics viewpoints. The results are found to be satisfactory with respect to the experimental data.

    Comments:
    8 pages, 8 figures, submitted in Physical Review C (R)
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1908.07983 [pdf]
    NPA(2020)·6 citations

Affiliations

first authorsco-authorsvia INSPIRE