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Nuclear Theory·nucl-th

Friday·February 22, 2019

5 papers—3 primary·2 cross-listed

All5Primary3Cross-lists2
  1. 01

    [Submitted on 21 Feb 2019]

    Disentangling fission fragment evaporation models using TALYS

    Andreas Solders · Andrea Mattera · Ali Al-Adili · Mattias Lantz · Vasileios Rakopoulos · Stephan Pomp

    Several computer codes based on phenomenological models are being developed with the aim of obtaining fission observables, such as neutron and gamma multiplicities and product yields. Key points in these calculations, which are handled differently by the various codes, are the sharing of the total excitation energy between the fragments and the generation of angular momenta. After the initial states of the fragments is set, the de-excitation through the emission of neutrons and photons can be model. However, many models also include tunable parameters that are used to make the calculations conform with literature data. As a result, it could be possible to obtain good agreement with experimental results even with questionable assumptions on the initial conditions. To test the assumptions made by different fission models the code DEFIN has been developed. DEFIN starts with the fission fragments as generated by the models and calculates the average neutron emission as a function of mass in a transparent and coherent way using the nuclear reaction code TALYS. Hence, the probabilities of neutron emission in competition with de-excitation comes from parameters of the TALYS code that have not been optimised. The results are then compared looking at general trends and at the difference to what is obtained with the stand-alone versions of the codes. In this study, the output of DEFIN for five of the most commonly used fission codes is compared to the results of the stand-alone versions, and to experimental data, for the reactions U(n,f), Pu(n,f) and Cf(sf).

    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1902.08114 [pdf]
    0 citations
  2. 02

    [Submitted on 21 Feb 2019]

    Limiting magnetic field for minimal deformation of a magnetised neutron star

    R. O. Gomes · Helena Pais · V. Dexheimer · Constança Providência · S. Schramm

    In this work we study the structure of neutron stars under the effect of a poloidal magnetic field and determine the limiting highest magnetic field intensity which still allows a satisfactory description of magnetic neutron stars in the spherical symmetry regime. We describe different compositions of stars (nucleonic, hyperonic, and hybrid), using three state-of-the-art relativistic mean field models for the microscopic description of matter, which are in agreement with experimental and observational data. The structure of stars is described by the general relativistic solution of both Einstein's field equations assuming a spherical symmetry, and Einstein-Maxwell's field equations assuming an axi-symmetric deformation. We find a limiting magnetic moment of the order of Am, which corresponds to magnetic fields of the order of 10 G at the surface, and G at the centre of the star, above which the deformation due to the magnetic field is not negligible. We show that the intensity of the magnetic field developed in the star depends on the EoS, and, for a given baryonic mass and fixed magnetic moment, larger fields are attained with softer EoS. We also show that the appearance of exotic degrees of freedom, such as hyperons or a quark core, is disfavored in the presence of a very strong magnetic field. As a consequence, a highly magnetized nucleonic star may suffer an internal conversion due to the decay of the magnetic field, which could be accompanied by a sudden cooling of the star or a gamma ray burst.

    Subjects:
    Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR)
    arXiv:
    1902.08146 [pdf]
    Astron.Astrophys.(2019)·35 citations
  3. 03

    [Submitted on 21 Feb 2019]

    Scattering amplitudes versus potentials in nuclear effective field theory: search for a potential compromise

    Manuel Pavon Valderrama🇨🇳

    In effective field theory physical quantities, in particular observables, are expressed as a power series in terms of a small expansion parameter. For non-perturbative systems, for instance nuclear physics, this requires the non-perturbative treatment of at least part of the interaction (or the potential, if one is dealing with a non-relativistic system), while the rest of the interaction is included as perturbations. This is not entirely trivial and as a consequence different interpretations on how to treat these systems have appeared. A practical approach is to expand the effective potential, where this potential is later fully iterated in the Schroedinger equation for obtaining amplitudes and observables. The expectation is that this will lead to observables that will have an implicit power counting expansion. Here I explicitly check whether the amplitudes (when expanded according to the counting) are actually following the same power counting as the potential. It happens that reality does not necessarily conform to expectations and the amplitudes will sometimes violate the power counting with which the potential has been expanded. A more formal approach is to formulate the expansion directly in terms of amplitudes and observables, which is the original aim of the effective field theory idea. Yet this second approach is technically complicated. I explore here the possibility of constructing potentials that when fully iterated will make sure that amplitudes are indeed expansible in terms of a small expansion parameter.

    Comments:
    23 pages, 10 figures, 6 tables, now it actually corresponds to the accepted version (PRC)
    Subjects:
    Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
    arXiv:
    1902.08172 [pdf]
    PRC(2025)·22 citations
  4. 04

    [Submitted on 21 Feb 2019] (cross-list from hep-ph)

    Violation of Wiedemann-Franz Law for Hot Hadronic Matter created at NICA, FAIR and RHIC Energies using Non-extensive Statistics

    Rutuparna Rath🇮🇳 · Sushanta Tripathy🇮🇳 · Bhaswar Chatterjee🇮🇳 · Raghunath Sahoo🇮🇳 · Swatantra K. Tiwari🇮🇳 · Abhishek Nath🇮🇳

    We present here the computation of electrical and thermal conductivity by solving the Boltzmann transport equation in relaxation time approximation. We use the -generalized Boltzmann distribution function to incorporate the effects of non-extensivity. The behaviour of these quantities with changing temperature and baryochemical potential has been studied as the system slowly moves towards thermodynamic equilibrium. We have estimated the Lorenz number at NICA, FAIR and the top RHIC energies and studied as a function of temperature, baryochemical potential and the non-extensive parameter, . We have observed that Wiedemann-Franz law is violated for a non-extensive hadronic phase as well as for an equilibrated hadron gas at high temperatures.

    Comments:
    Same as the published version
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
    arXiv:
    1902.07922 [pdf]
    EPJA(2019)·13 citations
  5. 05

    [Submitted on 21 Feb 2019] (cross-list from hep-ph)

    The strong running coupling from the gauge sector of Domain Wall lattice QCD with physical quark masses

    S. Zafeiropoulos🇩🇪 · Ph. Boucaud🇫🇷 · F. De Soto🇪🇸 · J. Rodríguez-Quintero🇪🇸 · J. Segovia🇪🇸

    We report on the first computation of the strong running coupling at the physical point (physical pion mass) from the ghost-gluon vertex, computed from lattice simulations with three flavors of Domain Wall fermions. We find , in remarkably good agreement with the world-wide average. Our computational bridge to this value is the Taylor-scheme strong coupling, which has been revealed of great interest by itself because it can be directly related to the quark-gluon interaction kernel in continuum approaches to the QCD bound-state problem.

    Comments:
    6 pages, 3 figures, v2: references added
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Lattice (hep-lat); Nuclear Theory (nucl-th)
    arXiv:
    1902.08148 [pdf]
    PRL(2019)·86 citations

Affiliations

first authorsco-authorsvia INSPIRE