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Nuclear Theory·nucl-th

Thursday·February 25, 2016

7 papers—7 primary·0 cross-listed

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  1. 01

    [Submitted on 23 Feb 2016]

    Threshold pion production in proton-proton collisions at NNLO in chiral EFT

    V. Baru🇩🇪 · E. Epelbaum🇩🇪 · A. A. Filin🇩🇪 · C. Hanhart🇩🇪 · H. Krebs🇩🇪 · F. Myhrer🇺🇸

    The reaction offers a good testing ground for chiral effective field theory at intermediate energies. It challenges our understanding of the first inelastic channel in nucleon-nucleon scattering and of the charge-symmetry breaking pattern in hadronic reactions. In our previous studies, we presented a complete calculation of the pion-production operator for s-wave pions up-to-and-including next-to-next-to-leading order (NNLO) in the formulation of chiral effective field theory, which includes pions, nucleons and degrees of freedom. In this paper we calculate the near threshold cross section for the reaction by performing the convolution of the obtained operators with nuclear wave functions based on modern phenomenological and chiral potentials. The available chiral wave functions are constructed with a cutoff comparable with the momentum transfer scale inherent in pion production reactions. Hence, a significant portion of the dynamical intermediate-range physics is thereby cut off by them. On the other hand, the NNLO amplitudes evaluated with phenomenological wave functions appear to be largely independent of the model used and give corrections to the dominant leading order contributions as expected from dimensional analysis. The result gives support to the counting scheme used to classify the pion production operators, which is a precondition for a reliable investigation of the chirally suppressed neutral pion production. The explicit inclusion of the is found to be important but smaller than expected due to cancellations.

    Comments:
    25 pages, 7 figures, 2 tables
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1602.07333 [pdf]
    EPJA(2016)·9 citations
  2. 02

    [Submitted on 23 Feb 2016]

    Nuclear structure theory of the heaviest nuclei

    A.V. Afanasjev · S.E. Agbemava

    The current status of the application of covariant density functional theory to the description of actinides and superheavy nuclei is reviewed. The achievements and open problems are discussed.

    Comments:
    14 pages, 7 figures, invited talk at the Zakopane Conference on Nuclear Physics "Extremes of the Nuclear Landscape", Zakopane, Poland, August 31 - September 7, 2014
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1602.07356 [pdf]
    Acta Phys.Polon.B(2015)·6 citations
  3. 03

    [Submitted on 24 Feb 2016]

    Primordial reaction and second Lithium puzzle

    A. M. Mukhamedzhanov · Shubhchintak · C. A. Bertulani

    During the Big Bang, was synthesized via the reaction. After almost 25 years of the failed attempts to measure the reaction in the lab at the Big Bang energies, just recently the LUNA collaboration presented the first successful measurements at two different Big Bang energies [M. Anders {\it et al.}, Phys. Rev. Lett. {\bf 113}, 042501 (2014)]. In this paper we will discuss how to improve the accuracy of the direct experiment. To this end the photon's angular distribution is calculated in the potential model. It contains contributions from electric dipole and quadrupole transitions and their interference, which dramatically changes the photon's angular distribution. The calculated distributions at different Big Bang energies have a single peak at . These calculations provide the best kinematic conditions to measure the reaction. The expressions for the total cross section and astrophysical factor are also derived by integrating the differential cross section over the photon's solid angle. The LUNA data are in excellent agreement with our calculations using a potential approach combined with a well established asymptotic normalization coefficient for . Comparisons of the available experimental data for the astrophysical factor and different calculations are presented. The Big Bang lithium isotopic ratio following from the LUNA data and the present analysis are discussed in the context of the disagreement between the observational data and the standard Big Bang model, which constitutes the second Lithium problem.

    Comments:
    26 pages, 2 figures, Version accepted for publication in Physical Review C
    Subjects:
    Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
    arXiv:
    1602.07395 [pdf]
    PRC(2016)·41 citations
  4. 04

    [Submitted on 24 Feb 2016]

    Effective potential from zero-momentum potential

    Janos Balog🇨🇳 · Pengming Zhang🇨🇳

    We obtain the centre-of-mass frame effective potential from the zero-momentum potential in Ruijsenaars-Schneider type 1-dimensional relativistic mechanics using classical inverse scattering methods.

    Comments:
    24 pages, 10 figures
    Subjects:
    Nuclear Theory (nucl-th); physics.class-ph (physics.class-ph)
    arXiv:
    1602.07498 [pdf]
    PTEP(2016)·1 citation
  5. 05

    [Submitted on 29 Jun 2015]

    Exact solution of equations for proton localization in neutron star matter

    Sebastian Kubis · Włodzimierz Wójcik

    The rigorous treatment of proton localization phenomenon in asymmetric nuclear matter is presented. The solution of proton wave function and neutron background distribution is found by the use of the extended Thomas-Fermi approach. The minimum of energy is obtained in the Wigner- Seitz approximation of spherically symmetric cell. The analysis of three different nuclear models suggests that the proton localization is likely to take place in the interior of neutron star.

    Comments:
    5 page, 4 figures
    Subjects:
    Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE)
    arXiv:
    1602.07511 [pdf]
    PRC(2015)·1 citation
  6. 06

    [Submitted on 24 Feb 2016]

    Application of an Extended Random Phase Approximation on Giant Resonances in Light, Medium and Heavy Mass Nuclei

    V. Tselyaev · N. Lyutorovich · J.Speth · S. Krewald · P.-G. Reinhard

    We present results of the time blocking approximation (TBA) on giant resonances in light, medium and heavy mass nuclei. The TBA is an extension of the widely used random-phase approximation (RPA) adding complex configurations by coupling to phonon excitations. A new method for handling the single-particle continuum is developed and applied in the present calculations. We investigate in detail the dependence of the numerical results on the size of the single particle space and the number of phonons as well as on nuclear matter properties. Our approach is self-consistent, based on an energy-density functional of Skyrme type where we used seven different parameter sets. The numerical results are compared with experimental data.

    Comments:
    17 pages, 12 figures
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1602.07518 [pdf]
    PRC(2016)·36 citations
  7. 07

    [Submitted on 24 Feb 2016]

    Hot and dense matter beyond relativistic mean field theory

    Xilin Zhang🇺🇸 · Madappa Prakash🇺🇸

    Properties of hot and dense matter are calculated in the framework of quantum hadro-dynamics by including contributions from two-loop (TL) diagrams arising from the exchange of iso-scalar and iso-vector mesons between nucleons. Our extension of mean-field theory (MFT) employs the same five density-independent coupling strengths which are calibrated using the empirical properties at the equilibrium density of iso-spin symmetric matter. Results of calculations from the MFT and TL approximations are compared for conditions of density, temperature, and proton fraction encountered in astrophysics applications involving compact objects. The TL results for the equation of state (EOS) of cold pure neutron matter at sub- and near-nuclear densities agree well with those of modern quantum Monte Carlo and effective field-theoretical approaches. Although the high-density EOS in the TL approximation for neutron-star matter is substantially softer than its MFT counterpart, it is able to support a neutron star required by recent precise determinations. In addition, radii of stars are smaller by km than obtained in MFT. In contrast to MFT, the TL results also give a better account of the single-particle or optical potentials extracted from analyses of medium-energy proton-nucleus and heavy-ion experiments. In degenerate conditions, the thermal variables are well reproduced by results of Landau's Fermi-Liquid theory in which density-dependent effective masses feature prominently. The ratio of the thermal components of pressure and energy density expressed as , often used in astrophysical simulations, exhibits a stronger dependence on density than on proton fraction and temperature in both MFT and TL calculations. The prominent peak of at supra-nuclear density found in MFT is, however, suppressed in TL calculations.

    Comments:
    53 page, 24 figures, and 3 tables
    Subjects:
    Nuclear Theory (nucl-th); Solar and Stellar Astrophysics (astro-ph.SR)
    arXiv:
    1602.07665 [pdf]
    PRC(2016)·15 citations

Affiliations

first authorsco-authorsvia INSPIRE