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Nuclear Theory·nucl-th

Wednesday·April 8, 2015

8 papers—5 primary·3 cross-listed

All8Primary5Cross-lists3
  1. 01

    [Submitted on 7 Apr 2015]

    Large amplitude collective dynamic beyond the independent particle/quasiparticle picture

    Denis Lacroix

    In the present note, a summary of selected aspects of time-dependent mean-field theory is first recalled. This approach is optimized to describe one-body degrees of freedom. A special focus is made on how this microscopic theory can be reduced to a macroscopic dynamic for a selected set of collective variables. Important physical phenomena like adiabaticity/diabaticity, one-body dissipation or memory effect are discussed. Special aspects related to the use of a time-dependent density functional instead of a time-dependent Hartree-Fock theory based on a bare hamiltonian are underlined. The absence of proper description of complex internal correlations however strongly impacts the predictive power of mean-field. A brief overview of theories going beyond the independent particles/quasi-particles theory is given. Then, a special attention is paid for finite fermionic systems at low internal excitation. In that case, quantum fluctuations in collective space that are poorly treated at the mean-field level, are important. Several approaches going beyond mean-field, that are anticipated to improve the description of quantum fluctuations, are discussed: the Balian-Vénéroni variational principle, the Time-Dependent Random Phase Approximation and the recently proposed Stochastic Mean-Field theory. Relations between these theories are underlined as well as their advantages and shortcomings.

    Comments:
    To be published in the ebook "Progress of time-dependent nuclear reaction theory" honoring Prof. Joachim Maruhn's retirement
    Subjects:
    Nuclear Theory (nucl-th); Strongly Correlated Electrons (cond-mat.str-el); Nuclear Experiment (nucl-ex)
    arXiv:
    1504.01499 [pdf]
    7 citations
  2. 02

    [Submitted on 7 Apr 2015]

    Equation of State in a Generalized Relativistic Density Functional Approach

    Stefan Typel🇩🇪

    The basic concepts of a generalized relativistic density functional approach to the equation of state of dense matter are presented. The model is an extension of relativistic mean-field models with density-dependent couplings. It includes explicit cluster degrees of freedom. The formation and dissolution of nuclei is described with the help of mass shifts. The model can be adapted to the description of finite nuclei in order to study the effect of -particle correlations at the nuclear surface on the neutron skin thickness of heavy nuclei. Further extensions of the model to include quark degrees of freedom or an energy dependence of the nucleon self-energies are outlined.

    Comments:
    6 pages, contribution to Proceedings of the workshop "Compact Stars in the QCD phase diagram IV", Prerow, Germany, September 26 - 30, 2014
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1504.01571 [pdf]
    4 citations
  3. 03

    [Submitted on 7 Apr 2015]

    Beta-decay properties of neutron-rich Ge, Se, Kr, Sr, Ru, and Pd isotopes from deformed quasiparticle random-phase approximation

    P. Sarriguren

    Beta-decay properties of even and odd-A neutron-rich Ge, Se, Kr, Sr, Ru, and Pd isotopes involved in the astrophysical rapid neutron capture process are studied within a deformed proton-neutron quasiparticle random-phase approximation. The underlying mean field is described self-consistently from deformed Skyrme Hartree-Fock calculations with pairing correlations. Residual interactions in the particle-hole and particle-particle channels are also included in the formalism. The isotopic evolution of the various nuclear equilibrium shapes and the corresponding charge radii are investigated in all the isotopic chains. The energy distributions of the Gamow-Teller strength as well as the beta-decay half-lives are discussed and compared with the available experimental information. It is shown that nuclear deformation plays a significant role in the description of the decay properties in this mass region. Reliable predictions of the strength distributions are essential to evaluate decay rates in astrophysical scenarios.

    Comments:
    16 pages, 26 figures. arXiv admin note: text overlap with arXiv:1403.1049
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1504.01640 [pdf]
    PRC(2015)·57 citations
  4. 04

    [Submitted on 7 Apr 2015]

    Eta photoproduction in a combined analysis of pion- and photon-induced reactions

    D. Rönchen🇩🇪 · M. Döring🇺🇸 · H. Haberzettl🇺🇸 · J. Haidenbauer🇩🇪 · U.-G. Meißner🇩🇪 · K. Nakayama🇩🇪

    The final state is isospin-selective and thus provides access to the spectrum of excited nucleons without being affected by excited states. To this end, the world database on eta photoproduction off the proton up to a center-of-mass energy of GeV is analyzed, including data on differential cross sections, and single and double polarization observables. The resonance spectrum and its properties are determined in a combined analysis of eta and pion photoproduction off the proton together with the reactions , , and . For the analysis, the so-called Jülich coupled-channel framework is used, incorporating unitarity, analyticity, and effective three-body channels. Parameters tied to photoproduction and hadronic interactions are varied simultaneously. The influence of recent MAMI and asymmetry data on the eta photoproduction amplitude is discussed in detail.

    Comments:
    21 pages, 10 figures. Updated to the published version
    Subjects:
    Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
    arXiv:
    1504.01643 [pdf]
    EPJA(2015)·100 citations
  5. 05

    [Submitted on 7 Apr 2015]

    Breaking and restoration of rotational symmetry for irreducible tensor operators on the lattice

    Bing-Nan Lu🇩🇪 · Timo A. Lähde🇩🇪 · Dean Lee🇺🇸 · Ulf-G. Meißner🇩🇪

    We study the breaking of rotational symmetry on the lattice for irreducible tensor operators and practical methods for suppressing this breaking. We illustrate the features of the general problem using an cluster model for Be. We focus on the lowest states with non-zero angular momentum and examine the matrix elements of multipole moment operators. We show that the physical reduced matrix element is well reproduced by averaging over all possible orientations of the quantum state, and this is expressed as a sum of matrix elements weighted by the corresponding Clebsch-Gordan coefficients. For our cluster model we find that the effects of rotational symmetry breaking can be largely eliminated for lattice spacings of fm, and we expect similar improvement for actual lattice Monte Carlo calculations.

    Comments:
    8 pages, 4 figures
    Subjects:
    Nuclear Theory (nucl-th); High Energy Physics — Lattice (hep-lat)
    arXiv:
    1504.01685 [pdf]
    PRD(2015)·15 citations

Affiliations

first authorsco-authorsvia INSPIRE