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Nuclear Theory·nucl-th

Wednesday·December 7, 2016

11 papers—6 primary·5 cross-listed

All11Primary6Cross-lists5
  1. 07

    [Submitted on 5 Dec 2016] (cross-list from hep-ph)

    Light Axial Vectors, Nuclear Transitions, and the Be Anomaly

    Jonathan Kozaczuk🇺🇸 · David E. Morrissey🇨🇦 · S. R. Stroberg🇨🇦

    New hidden particles could potentially be emitted and discovered in rare nuclear transitions. In this work we investigate the production of hidden vector bosons with primarily axial couplings to light quarks in nuclear transitions, and we apply our results to the recent anomaly seen in Be decays. The relevant matrix elements for transitions are calculated using methods with inter-nucleon forces derived from chiral effective field theory and the in-medium similarity renormalization group. We find that the emission of a light axial vector with mass can account for the anomaly seen in the isoscalar transition together with the absence of a significant anomaly in the corresponding isovector transition. We also show that such an axial vector can be derived from an anomaly-free ultraviolet-complete theory that is consistent with current experimental data.

    Comments:
    v2: Minor corrections, conclusions unchanged. Matches version published in PRD
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
    arXiv:
    1612.01525 [pdf]
    PRD(2017)·91 citations
  2. 08

    [Submitted on 5 Dec 2016] (cross-list from hep-lat)

    Lattice QCD spectroscopy for hadronic CP violation

    Jordy de Vries🇳🇱 · Emanuele Mereghetti🇺🇸 · Chien-Yeah Seng🇨🇳 · Andre Walker-Loud🇺🇸

    The interpretation of nuclear electric dipole moment (EDM) experiments is clouded by large theoretical uncertainties associated with nonperturbative matrix elements. In various beyond-the-Standard Model scenarios nuclear and diamagnetic atomic EDMs are expected to be dominated by CP-violating pion-nucleon interactions that arise from quark chromo-electric dipole moments. The corresponding CP-violating pion-nucleon coupling strengths are, however, poorly known. In this work we propose a strategy to calculate these couplings by using spectroscopic lattice QCD techniques. Instead of directly calculating the pion-nucleon coupling constants, a challenging task, we use chiral symmetry relations that link the pion-nucleon couplings to nucleon sigma terms and mass splittings that are significantly easier to calculate. In this work, we show that these relations are reliable up to next-to-next-to-leading order in the chiral expansion in both SU(2) and SU(3) chiral perturbation theory. We conclude with a brief discussion about practical details regarding the required lattice QCD calculations and the phenomenological impact of an improved understanding of CP-violating matrix elements.

    Comments:
    16 pages, 2 figures; v2 version accepted for publication
    Subjects:
    High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
    arXiv:
    1612.01567 [pdf]
    PLB(2017)·46 citations
  3. 09

    [Submitted on 6 Dec 2016] (cross-list from gr-qc)

    The stability of relativistic stars and the role of the adiabatic index

    Ch.C. Moustakidis

    We study the stability of three analytical solutions of the Einstein's field equations for spheres of fluid. These solutions are suitable to describe compact objects including white dwarfs, neutron stars and supermassive stars and they have been extensively employed in the literature. We re-examine the range of stability of the Tolman VII solution, we focus on the stability of the Buchdahl solution which is under contradiction in the literature and we examine the stability of the Nariai IV solution. We found that all the mentioned solutions are stable in an extensive range of the compactness parameter. We also concentrate on the effect of the adiabatic index on the instability condition. We found that the critical adiabatic index, depends linearly on the ratio of central pressure over central energy density , up to high values of the compactness. Finally, we examine the possibility to impose constraints, via the adiabatic index, on realistic equations of state in order to ensure stable configurations of compact objects.

    Comments:
    17 pages, 14 figures, 2 tables
    Subjects:
    General Relativity and Quantum Cosmology (gr-qc); High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR); Nuclear Theory (nucl-th)
    arXiv:
    1612.01726 [pdf]
    Gen.Rel.Grav.(2017)·216 citations
  4. 10

    [Submitted on 5 Dec 2016] (cross-list from astro-ph.HE)

    Mixing of charged and neutral Bose condensates at nonzero temperature and magnetic field

    Alexander Haber🇬🇧 · Andreas Schmitt🇬🇧

    It is expected that in the interior of compact stars a proton superconductor coexists with and couples to a neutron superfluid. Starting from a field-theoretical model for two complex scalar fields - one of which is electrically charged - we derive a Ginzburg-Landau potential which includes entrainment between the two fluids and temperature effects from thermal excitations of the two scalar fields and the gauge field. The Ginzburg-Landau description is then used for an analysis of the phase structure in the presence of an external magnetic field. In particular, we study the effect of the superfluid on the flux tube phase by computing the various critical magnetic fields and deriving an approximation for the flux tube interaction. As a result, we point out differences to the naive expectations from an isolated superconductor, for instance the existence of a first-order flux tube onset, resulting in a more complicated phase structure in the region between type-I and type-II superconductivity.

    Comments:
    11 pages, contribution to the proceedings of "Quark Confinement and the Hadron Spectrum XII", Aug 28 - Sep 4, 2016, in Thessaloniki, Greece; v2: small corrections in Eqs. (9) and (13), references added
    Subjects:
    High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
    arXiv:
    1612.01865 [pdf]
    EPJ Web Conf.(2017)·7 citations
  5. 11

    [Submitted on 6 Dec 2016] (cross-list from hep-lat)

    Evidence of effective axial U(1) symmetry restoration at high temperature QCD

    A. Tomiya🇨🇳 · G. Cossu🇬🇧 · S. Aoki🇯🇵 · H. Fukaya🇯🇵 · S. Hashimoto🇯🇵 · T. Kaneko🇯🇵 · J. Noaki🇯🇵

    We study the axial U(1) symmetry at finite temperature in two-flavor lattice QCD. Employing the Mobius domain-wall fermions, we generate gauge configurations slightly above the critical temperature Tc with different lattice sizes L = 2-4 fm. Our action allows frequent topology tunneling while keeping good chiral symmetry close enough to that of overlap fermions. This allows us to recover full chiral symmetry by an overlap/domain-wall reweighting. Above the phase transition, a strong suppression of the low-lying modes is observed in both of overlap and domain-wall Dirac spectra. We, however, find a sizable violation of the Ginsparg-Wilson relation in the Mobius domain-wall Dirac eigenmodes, which dominates the signals of the axial U(1) symmetry breaking near the chiral limit. We also find that the use of overlap fermion only in the valence sector is dangerous since it suffers from the artifacts due to partial quenching. Reweighting the Mobius domain-wall fermion determinant to that of the overlap fermion, we observe the axial U(1) breaking to vanish in the chiral limit, which is stable against the changes of the lattice volume and lattice spacing.

    Comments:
    29 pages, 14 figures, references are updated
    Subjects:
    High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
    arXiv:
    1612.01908 [pdf]
    PRD(2017)·144 citations

Affiliations

first authorsco-authorsvia INSPIRE