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Nuclear Theory·nucl-th

Thursday·September 6, 2018

9 papers—6 primary·3 cross-listed

All9Primary6Cross-lists3
  1. 01

    [Submitted on 4 Sept 2018]

    Neutron star cooling with a dynamic stellar structure

    J. M. Dong🇨🇳 · L. J. Wang🇺🇸 · W. Zuo🇨🇳

    The observations combined with theory of neutron star (NS) cooling play a crucial role in achieving the intriguing information of the stellar interior, such as the equation of state (EOS), composition and superfluidity of dense matter. The traditional NS cooling theory is based on the assumption that the stellar structure does not change with time. The validity of such a static description has not yet been confirmed. We generalize the theory to a dynamic treatment; that is, continuous change of the NS structure (rearrangement of the stellar density distribution with the total baryon number fixed) as the decrease of temperature during the thermal evolution, is taken into account. It is found that the practical thermal energy used for the cooling is slightly lower than that is estimated in static situation, and hence the cooling of NSs is accelerated correspondingly but the effect is rather weak. Therefore, the static treatment is a good approximation in the calculations of NS cooling.

    Comments:
    13 pages, 6 figures
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1809.01134 [pdf]
    ApJ(2018)·5 citations
  2. 02

    [Submitted on 4 Sept 2018]

    ADG: Automated generation and evaluation of many-body diagrams I. Bogoliubov many-body perturbation theory

    Pierre Arthuis🇫🇷 · Thomas Duguet🇫🇷 · Alexander Tichai🇫🇷 · Raphaël-David Lasseri🇫🇷 · Jean-Paul Ebran🇫🇷

    We describe the first version (v1.0.0) of the code ADG that automatically (1) generates all valid Bogoliubov many-body perturbation theory (BMBPT) diagrams and (2) evaluates their algebraic expression to be implemented for numerical applications. This is achieved at any perturbative order for a Hamiltonian containing both two-body (four-legs) and three-body (six-legs) interactions (vertices). The automated generation of BMBPT diagrams of order relies on elements of graph theory, i.e., it is achieved by producing all oriented adjacency matrices of size satisfying topological Feynman's rules. The automated evaluation of BMBPT diagrams of order relies both on the application of algebraic Feynman's rules and on the identification of a powerful diagrammatic rule providing the result of the remaining -tuple time integral. The diagrammatic rule in question constitutes a novel finding allowing for the straight summation of large classes of time-ordered diagrams at play in the time-independent formulation of BMBPT. Correspondingly, the traditional resolvent rule employed to compute time-ordered diagrams happens to be a particular case of the general rule presently identified. The code ADG is written in Python2.7 and uses the graph manipulation package NetworkX. The code is also able to generate and evaluate Hartree-Fock-MBPT (HF-MBPT) diagrams and is made flexible enough to be expanded throughout the years to tackle the diagrammatics at play in various many-body formalisms that already exist or are yet to be formulated.

    Comments:
    32 pages, 22 figures, 6 tables
    Subjects:
    Nuclear Theory (nucl-th); Strongly Correlated Electrons (cond-mat.str-el); Atomic Physics (physics.atom-ph); physics.chem-ph (physics.chem-ph)
    arXiv:
    1809.01187 [pdf]
    Comput.Phys.Commun.(2019)·48 citations
  3. 03

    [Submitted on 4 Sept 2018]

    The non-equilibrium attractor for kinetic theory in relaxation time approximation

    Michael Strickland🇺🇸

    I demonstrate that the concept of a non-equilibrium attractor can be extended beyond the lowest-order moments typically considered in hydrodynamic treatments. Using a previously obtained exact solution to the relaxation-time approximation Boltzmann equation for a transversally homogeneous and boost-invariant system subject to Bjorken flow, I derive an equation obeyed by all moments of the one-particle distribution function. Using numerical solutions, I show that, similar to the pressure anisotropy, all moments of the distribution function exhibit attractor-like behavior wherein all initial conditions converge to a universal solution after a short time with the exception of moments which are sensitive to modes with zero longitudinal momentum and high transverse momentum. In addition, I compute the exact solution for the distribution function itself on very fine lattices in momentum space and demonstrate that (a) an attractor for the full distribution function exists and (b) solutions with generic initial conditions relax to this solution, first at low momentum and later at high momentum.

    Comments:
    27 pages, 13 figures; v3: updates to Figs. 2, 3, 9, 10, and 11; note added; no changes required to discussion or conclusions
    Subjects:
    Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
    arXiv:
    1809.01200 [pdf]
    JHEP(2018)·129 citations
  4. 04

    [Submitted on 5 Sept 2018]

    Gogny-force derived effective shell-model Hamiltonian

    Weiguang Jiang🇨🇳 · Baishan Hu🇨🇳 · Zhonghao Sun🇨🇳 · Furong Xu🇨🇳

    The density-dependent finite-range Gogny force has been used to derive the effective Hamiltonian for the shell-model calculations of nuclei. The density dependence simulates an equivalent three-body force, while the finite range gives a Gaussian distribution of the interaction in the momentum space and hence leads to an automatic smooth decoupling between low-momentum and high-momentum components of the interaction, which is important for finite-space shell-model calculations. Two-body interaction matrix elements, single-particle energies and the core energy of the shell model can be determined by the unified Gogny force. The analytical form of the Gogny force is advantageous to treat cross-shell cases, while it is difficult to determine the cross-shell matrix elements and single-particle energies using an empirical Hamiltonian by fitting experimental data with a large number of matrix elements. In this paper, we have applied the Gogny-force effective shell-model Hamiltonian to the - and -shell nuclei. The results show good agreements with experimental data and other calculations using empirical Hamiltonians. The experimentally-known neutron drip line of oxygen isotopes and the ground states of typical nuclei B and N can be reproduced, in which the role of three-body force is non-negligible. The Gogny-force derived effective Hamiltonian has also been applied to the cross-shell calculations of the - shell.

    Comments:
    23 pages, 11 figures
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1809.01292 [pdf]
    PRC(2018)·9 citations
  5. 05

    [Submitted on 5 Sept 2018]

    Yakubovsky scheme to study the 4- and 5-nucleon systems in the case of alpha-state structure with spin-dependent nucleon-nucleon potentials

    E. Ahmadi Pouya🇮🇷 · A.A. Rajabi🇮🇷

    In this project, we have investigated the 5-nucleon model system in the picture of the specific alpha-state structure, by extending the Yakubovsky scheme with the inclusion of the spin and isospin degrees of freedom. The Yakubovsky formalism for the 5-nucleon system in the effective alpha-neutron attractive model leads to a set of two coupled equations, based on two relevant alpha-nucleon sub-cluster components. To this regard, by switching off the fifth nucleon interactions, the 5-nucleon Yakubovsky equations can be reduced to a typical 4-nucleon problem. To calculate the 5- and 4-nucleon bound state equations, the coupled equations are projected in the momentum space in terms of the Jacobi momenta. In the calculations two different spin-dependent and one spinindependent nucleon-nucleon potential types are dedicated, such as Afnan-Tang S3, Malfliet-Tjon I/III and Volkov potentials,respectively. The some obtained binding energy differences between the 4-nucleon system in the alpha-state and the 5-nucleon system in the case of alpha-nucleon structure demonstrating the effective interaction between the alpha and an attractive neutron. The obtained results for the effective interaction are consistent either for spin-independent and spin-dependent interactions. Also,the binding energy results are in excellent compatibility with the achieved results by other techniques.

    Comments:
    PACS. No: 21.45.+v; 21.30.Fe; 21.30.-x; 21.10.Dr
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1809.01373 [pdf]
    Karbala International Journal of Modern Science(2017)·0 citations
  6. 06

    [Submitted on 5 Sept 2018]

    Quartet structure of nuclei in a boson formalism: the case of Si

    M. Sambataro · N. Sandulescu

    The structure of the nucleus Si is studied by resorting to an IBM-type formalism with and bosons representing isospin and angular momentum and quartets, respectively. quartets are four-body correlated structures formed by two protons and two neutrons. The microscopic nature of the quartet bosons, meant as images of the fermionic quartets, is investigated by making use of a mapping procedure and is supported by the close resemblance between the phenomenological and microscopically derived Hamiltonians. The ground state band and two low-lying side bands, a and a band, together with all known transitions and quadrupole moments associated with these states are well reproduced by the model. An analysis of the potential energy surface places Si, only known case so far, at the critical point of the U(5)- transition of the IBM structural diagram.

    Comments:
    To appear in Physics Letters B
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1809.01421 [pdf]
    PLB(2018)·3 citations

Affiliations

first authorsco-authorsvia INSPIRE