PaperPanorama
FAQ

Nuclear Theory·nucl-th

Thursday·April 18, 2019

11 papers—5 primary·6 cross-listed

All11Primary5Cross-lists6
  1. 06

    [Submitted on 16 Apr 2019] (cross-list from hep-ph)

    Spontaneous generation of spin current from the vacuum by strong electric fields

    Xu-Guang Huang🇨🇳 · Mamoru Matsuo🇨🇳 · Hidetoshi Taya🇨🇳

    We discuss spontaneous spin current generation from the vacuum by strong electric fields as a result of interplay between the Schwinger mechanism and a spin-orbit coupling. By considering a homogeneous slow strong electric field superimposed by a fast weak transverse electric field, we explicitly evaluate the vacuum expectation value of a spin current (the Bargmann-Wigner spin current) by numerically solving the Dirac equation. We show that a non-vanishing spin current polarized in the direction perpendicular to the electric fields flows mostly in the longitudinal direction. We also find that a relativistic effect due to the helicity conservation affects direction/polarization of spin current.

    Comments:
    v2: 16 pages, 5 figures; discussions and references added
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); cond-mat.mtrl-sci (cond-mat.mtrl-sci); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
    arXiv:
    1904.07593 [pdf]
    PTEP(2019)·12 citations
  2. 07

    [Submitted on 16 Apr 2019] (cross-list from astro-ph.HE)

    Improved photomeson model for interactions of cosmic ray nuclei

    Leonel Morejon🇩🇪 · Anatoli Fedynitch🇩🇪 · Denise Boncioli🇩🇪 · Daniel Biehl🇩🇪 · Walter Winter🇩🇪

    Photon-hadronic interactions are important for the sources and the transport of Ultra-High Energy Cosmic Rays (UHECRs). Current state-of-the-art cosmic ray transport simulations handle nuclear disintegration at energies of the Giant Dipole Resonance at a more sophisticated level, as well as the photohadronic interactions of nucleons in the high-energy regime above the pion production threshold. However, the interactions of nuclei above the pion production threshold are commonly modeled by treating the nucleus as a superposition of free nucleons -- ignoring the effect of the nuclear medium. We construct an improved, inclusive model for the photomeson regime for nuclei with by employing more accurate, data-driven parametrizations of the interaction cross section, the fragmentation of the primary nucleus and the inclusive pion production cross section that directly affects the production of astrophysical neutrinos. We apply our results to two multi-messenger scenarios (Tidal Disruption Events and Gamma-Ray Bursts) in which photonuclear interactions in the photomeson regime are the dominant cooling process for the highest energy cosmic rays. While we find moderate changes to the mass composition of UHECRs, the astrophysical neutrino fluxes exhibit a significant (factor of a few) reduction compared to the naïve superposition of free nucleons for sources of UHECR nuclei with a populated cascade. The numerical code implementing the model has been made publicly available, which facilitates the integration of our results in similar frameworks.

    Comments:
    Accepted for publication in JCAP. Main changes from previous version: 1.Corrected treatment of the pion production at high energies. 2.Added two new figures comparing the model to experimental data. Software tools available at https://github.com/mohller/AstroPhoMes/ Cite the code using the DOI 10.5281/zenodo.2600177
    Subjects:
    High Energy Astrophysical Phenomena (astro-ph.HE); Nuclear Theory (nucl-th)
    arXiv:
    1904.07999 [pdf]
    JCAP(2019)·48 citations
  3. 08

    [Submitted on 16 Apr 2019] (cross-list from hep-ph)

    Nucleon resonance contributions to unpolarised inclusive electron scattering

    A. N. Hiller Blin🇩🇪 · V. Mokeev🇺🇸 · M. Albaladejo🇺🇸 · C. Fernández-Ramírez🇲🇽 · V. Mathieu🇺🇸 · A. Pilloni🇮🇹 · A.Szczepaniak🇺🇸 · V. D. Burkert🇺🇸 · V. V. Chesnokov🇷🇺 · A. A. Golubenko🇷🇺 · M. Vanderhaeghen🇩🇪

    The first CLAS12 experiments will provide high-precision data on inclusive electron scattering observables at a photon virtuality ranging from 0.05 GeV to 12 GeV and center-of-mass energies up to 4 GeV. In view of this endeavour, we present the modeling of the resonant contributions to the inclusive electron scattering observables. As input, we use the existing CLAS electrocoupling results obtained from exclusive meson electroproduction data off protons, and evaluate for the first time the resonant contributions based on the experimental results on the nucleon resonance electroexcitation. The uncertainties are given by the data and duly propagated through a Monte Carlo approach. In this way, we obtain estimates for the resonant contributions, important for insight into the nucleon parton distributions in the resonance region and for the studies of quark-hadron duality.

    Subjects:
    High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
    arXiv:
    1904.08016 [pdf]
    PRC(2019)·46 citations
  4. 09

    [Submitted on 17 Apr 2019] (cross-list from hep-ph)

    Spin-dependent dynamically assisted Schwinger mechanism

    Xu-Guang Huang🇨🇳 · Hidetoshi Taya🇨🇳

    We study electron and positron pair production from the vacuum by a strong slow electric field superimposed by a weak fast electric field pointing in an arbitrary direction as a perturbation (the dynamically assisted Schwinger mechanism). An analytical formula for the production number is derived on the basis of the perturbation theory in the Furry picture. The formula is found to be in good agreement with non-perturbative results obtained by numerically solving the Dirac equation if the perturbation is sufficiently weak and/or is not very slow. We also find analytically/numerically that the Schwinger mechanism becomes spin-dependent if the perturbation has a transverse component with respect to the strong electric field. The number difference between spin up and down particles is strongly suppressed by an exponential of the critical field strength if the frequency of the perturbation is small, while it is only weakly suppressed by powers of the critical field strength if the frequency is large enough. We also find that the spin-imbalance exhibits non-trivial oscillating behaviors in terms of the frequency of the perturbation, the azimuthal angle, and the momentum of produced particles.

    Comments:
    23 pages, 11 figures; v2: results for the total production number are added, the validity of the perturbative approach is discussed in more detail, figures are improved, typos are corrected, version to be published in PRD
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th); Plasma Physics (physics.plasm-ph); Quantum Physics (quant-ph)
    arXiv:
    1904.08200 [pdf]
    PRD(2019)·27 citations
  5. 10

    [Submitted on 17 Apr 2019] (cross-list from hep-ph)

    Angular mode expansion of the Boltzmann equation in the small-angle approximation

    Jean-Paul Blaizot🇫🇷 · Naoto Tanji🇮🇹

    We use an expansion in angular mode functions in order to solve the Boltzmann equation for a gluon plasma undergoing longitudinal expansion. By comparing with the exact solution obtained numerically by other means we show that the expansion in mode functions converges rapidly for all cases of practical interest, and represents a substantial gain in numerical effort as compared to more standard methods. We contrast the cases of a non expanding plasma and of longitudinally expanding plasmas, and follow in both cases the evolutions towards thermalization. In the latter case, we observe that, although the spherical mode function appears to be well reproduced after some time by a local equilibrium distribution function depending on slowly varying temperature and chemical potential, thereby suggesting thermalization of the system, the longitudinal and transverse pressures take more time to equilibrate. This is because the expansion hinders the relaxation of the first angular mode function. This feature was also observed in a simpler context where the Boltzmann equation is solved in terms of special moments within the relaxation time approximation, and attributed there to the particular coupling between the first two moments of the distribution function. The present analysis confirms this observation in a more realistic setting.

    Comments:
    23 pages, 16 figures, version published in Nuclear Physics A
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
    arXiv:
    1904.08244 [pdf]
    NPA(2019)·4 citations
  6. 11

    [Submitted on 17 Apr 2019] (cross-list from hep-ph)

    The analytic structure of thermodynamic systems with repulsive interactions

    Kirill Taradiy🇺🇦 · Anton Motornenko🇩🇪 · Volodymyr Vovchenko🇩🇪 · Mark I. Gorenstein🇺🇦 · Horst Stoecker🇩🇪

    Thermodynamic properties of systems with repulsive interactions, are considered in the grand canonical ensemble. The analytic structure of the excluded-volume model in the complex plane of the system chemical potential (fugacity) is elaborated, based on the fact that the pressure function can be given in terms of the Lambert W-function. Even though the excluded volume model has no phase transitions at real values of the chemical potential, it does exhibit a branch cut singularity in the complex plane, thus limiting the convergence range of the Taylor expansion in the chemical potential. Close similarities to analytic properties of the other models with repulsive interactions, such as a cluster expansion model, the mean-field model, and the ideal Fermi gas model, are pointed out. As an example, repulsive baryonic interactions in a hadron gas, with a focus on the fugacity/virial and Taylor expansion methods used in lattice QCD, are presented. The asymptotic behavior of the Fourier expansion coefficients in these various models suggests that the singular part of net baryonic density can to leading order be universally expressed in terms of polylogarithms.

    Comments:
    11 pages, 4 figures
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Lattice (hep-lat); Nuclear Theory (nucl-th)
    arXiv:
    1904.08259 [pdf]
    PRC(2019)·16 citations

Affiliations

first authorsco-authorsvia INSPIRE