PaperPanorama
FAQ

Nuclear Theory·nucl-th

Monday·November 2, 2015

6 papers—1 primary·5 cross-listed

All6Primary1Cross-lists5
  1. 01

    [Submitted on 30 Oct 2015]

    Impact of the Delta (1232) resonance on neutral pion photoproduction in chiral perturbation theory

    Lloyd W. Cawthorne · Judith A. McGovern

    We present an ongoing project to assess the importance of D-waves and the resonance for descriptions of neutral pion photoproduction in Heavy Baryon Chiral Perturbation Theory. This research has been motivated by data published by the A2 and CB-TAPS collaborations at MAMI [1]. This data has reached unprecedented levels of accuracy from threshold through to the resonance. Accompanying the experimental work, there has also been a series of publications studying the theory that show that, to go beyond an energy of MeV, it is necessary to include other aspects, in particular the as a degree of freedom [2] and possibly higher partial waves [3].

    Comments:
    Proceedings to the 8th International Workshop on Chiral Dynamics 2015
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1510.09136 [pdf]
    PoS(2016)·4 citations
  2. 02

    [Submitted on 29 Oct 2015] (cross-list from hep-ph)

    A light particle solution to the cosmic lithium problem

    Andreas Goudelis🇦🇹 · Maxim Pospelov🇨🇦 · Josef Pradler🇦🇹

    We point out that the cosmological abundance of Li can be reduced down to observed values if during its formation Big Bang Nucleosynthesis is modified by the presence of light electrically neutral particles that have substantial interactions with nucleons. We find that the lithium problem can be solved without affecting the precisely measured abundances of deuterium and helium if the following conditions are satisfied: the mass and lifetimes of such particles are bounded by and , and the abundance times the absorption cross section by either deuterium or Be are comparable to the Hubble rate, , at the time of Be formation. We include -initiated reactions into the primordial nucleosynthesis framework, observe that it leads to a substantial reduction of the freeze-out abundances of Li+Be, and find specific model realizations of this scenario. Concentrating on the axion-like-particle case, , we show that all these conditions can be satisifed if the coupling to -quarks is in the range of , which can be probed at intensity frontier experiments.

    Comments:
    5 pages, 4 figures; v2: minor improvements, matches published version
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); Cosmology and Nongalactic Astrophysics (astro-ph.CO); Nuclear Theory (nucl-th)
    arXiv:
    1510.08858 [pdf]
    PRL(2016)·53 citations
  3. 03

    [Submitted on 30 Oct 2015] (cross-list from hep-ph)

    Neutron capture and the antineutrino yield from nuclear reactors

    Patrick Huber🇺🇸 · Patrick Jaffke🇺🇸

    We identify a new, flux-dependent correction to the antineutrino spectrum as produced in nuclear reactors. The abundance of certain nuclides, whose decay chains produce antineutrinos above the threshold for inverse beta decay, has a nonlinear dependence on the neutron flux, unlike the vast majority of antineutrino producing nuclides, whose decay rate is directly related to the fission rate. We have identified four of these so-called nonlinear nuclides and determined that they result in an antineutrino excess at low-energies below 3.2MeV, dependent on the reactor thermal neutron flux. We develop an analytic model for the size of the correction and compare it to the results of detailed reactor simulations for various real existing reactors, spanning 3 orders of magnitude in neutron flux. In a typical pressurized water reactor the resulting correction can reach 0.9% of the low energy flux which is comparable in size to other, known low-energy corrections from spent nuclear fuel and the non-equilibrium correction. For naval reactors the nonlinear correction may reach the 10% level.

    Comments:
    5 pages, 2 figures, 2 tables
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
    arXiv:
    1510.08948 [pdf]
    PRL(2016)·27 citations
  4. 04

    [Submitted on 30 Oct 2015] (cross-list from hep-lat)

    Testing the degeneracy after low-mode removal with mesons

    M. Denissenya🇦🇹 · L. Glozman🇦🇹 · M. Pak🇦🇹

    Recent lattice results on Dirac low-mode removed mesons and baryons reveal the appearance of a new symmetry of confinement. Here the degeneracy of all iso-vector states within an irreducible representation of after low-mode removal is demonstrated. The symmetry contains and symmetries as subgroups and mixes all compontents of the two-flavor Dirac field. It implies the vanishing of the interaction of quarks with the color-magnetic field, which is shown by using the QCD Hamiltonian in Coulomb gauge.

    Comments:
    6 pages, 6 figures. Talk presented at the 33rd International Symposium on Lattice Field Theory (Lattice 2015), 14-18 July 2015, Kobe International Conference Center, Kobe, Japan
    Subjects:
    High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
    arXiv:
    1510.09015 [pdf]
    PoS(2016)·2 citations
  5. 05

    [Submitted on 30 Oct 2015] (cross-list from hep-ph)

    Inverse magnetic catalysis from the properties of the QCD coupling in a magnetic field

    Alejandro Ayala🇿🇦 · C. A. Dominguez🇿🇦 · L. A. Hernandez🇿🇦 · M. Loewe🇿🇦 · R. Zamora🇨🇱

    We compute the vacuum one-loop quark-gluon vertex correction at zero temperature in the presence of a magnetic field. From the vertex function we extract the effective quark-gluon coupling and show that it grows with increasing magnetic field strength. The effect is due to a subtle competition between the color charge associated to gluons and the color charge associated to quarks, the former being larger than the latter. In contrast, at high temperature the effective thermo-magnetic coupling results exclusively from the contribution of the color charge associated to quarks. This produces a decrease of the coupling with increasing field strength. We interpret the results in terms of a geometrical effect whereby the magnetic field induces, on average, a closer distance between the (electrically charged) quarks and antiquarks. At high temperature, since the effective coupling is proportional only to the color charge associated to quarks, such proximity with increasing field strength makes the effective coupling decrease due to asymptotic freedom. In turn, this leads to a decreasing quark condensate. In contrast, at zero temperature both the effective strong coupling and the quark condensate increase with increasing magnetic field. This is due to the color charge associated to gluons dominating over that associated to quarks, with both having the opposite sign. Thus, the gluons induce a kind of screening of the quark color charge, in spite of the quark-antiquark proximity. The implications of these results for the inverse magnetic catalysis phenomenon are discussed.

    Comments:
    Expanded discussion, references added. Version to appear in Phys. Lett. B
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Lattice (hep-lat); Nuclear Theory (nucl-th)
    arXiv:
    1510.09134 [pdf]
    PLB(2016)·81 citations
  6. 06

    [Submitted on 28 Oct 2015] (cross-list from hep-ph)

    Geometrical Models and Hadronic Radii

    Sarwat Zahra🇵🇰 · Haris Rashid🇵🇰 · Fazal-e-Aleem · Talab Hussain🇵🇰 · Abrar Ahmad Zafar🇵🇰 · Sohail Afzal Tahir🇵🇰

    By using electromagnetic form factors predicted by Generalized Chou Yang model (GCYM), we compute root mean square (rms) radii of several hadrons with varying strangeness content (number of strange quarks/anti-quarks) such as (pion, proton, phi0, Lambda0, Sigma+, Sigma- and Omega-) The computed radii are found quite consistent with the experimental results and those from other models (for pion and proton). For hadrons other than pion and proton, the experimental results are not available and also the GCYM and other models results are not consistent with each other. The computed rms radii (from GCYM and other models) indicate that rms radii decrease with increase in strangeness content, separately for mesons and baryons. The experimental results of hadrons other than pion and proton will throw more light on the suitability of GCYM and other models.

    Comments:
    Submitted to Chinese Physics C
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
    arXiv:
    1510.09146 [pdf]
    2 citations

Affiliations

first authorsco-authorsvia INSPIRE