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Nuclear Theory·nucl-th

Tuesday·September 22, 2015

20 papers—13 primary·7 cross-listed

All20Primary13Cross-lists7
  1. 14

    [Submitted on 5 May 2015] (cross-list from hep-th)

    Higher order fermion effective polynomial interactions

    Fabio L. Braghin🇧🇷

    Three different fermion effective potentials given by series of bilinears, , and also where and integer are investigated by introducing sets of auxiliary fields. A mininal procedure is adopted to deal with the auxiliary fields and an effective bosonized model in each case is found by assuming weak field fluctuations, i.e. weak enough when compared to (normalized) coupling constants. Different fermion condensates are considered for the ground state in the first two series analysed and the factorization of all higher order condensates into the lowest order one is found in most cases, i.e. in general . For the case of the third series built with vector-type bilinears no condensation is assumed to occur. The corresponding (weak) scalar fields effective models for the three cases are expanded in polynomial interactions. The resulting low energy effective boson model may a exhibit new approximate symmetry depending on the terms present in the original series-model and on the values of the coupling constants.

    Comments:
    Revised and extended version
    Subjects:
    High Energy Physics — Theory (hep-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
    arXiv:
    1505.01209 [pdf]
    Eur.Phys.J.Plus(2015)·2 citations
  2. 15

    [Submitted on 18 Sept 2015] (cross-list from hep-lat)

    The curvature of the freeze-out line in heavy ion collisions

    A. Bazavov🇺🇸 · H.-T. Ding🇨🇳 · P. Hegde🇨🇳 · O. Kaczmarek🇩🇪 · F. Karsch🇩🇪 · E. Laermann🇩🇪 · Swagato Mukherjee🇺🇸 · H. Ohno🇺🇸 · P. Petreczky🇺🇸 · C.Schmidt🇩🇪 · S. Sharma🇺🇸 · W. Soeldner🇩🇪 · M. Wagner🇺🇸

    We calculate the mean and variance of net-baryon number and net-electric charge distributions from Quantum Chromodynamics (QCD) using a next-to-leading order Taylor expansion in terms of temperature and chemical potentials. We compare these expansions with experimental data from STAR and PHENIX, determine the freeze-out temperature in the limit of vanishing baryon chemical potential, and, for the first time, constrain the curvature of the freeze-out line through a direct comparison between experimental data on net-charge fluctuations and a QCD calculation. We obtain a bound on the curvature coefficient, kappa_2^f < 0.011, that is compatible with lattice QCD results on the curvature of the QCD transition line.

    Comments:
    5 pages, 2 figures
    Subjects:
    High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
    arXiv:
    1509.05786 [pdf]
    PRD(2016)·45 citations
  3. 16

    [Submitted on 19 Sept 2015] (cross-list from hep-ph)

    Dileptons in a coarse-grained transport approach

    H. van Hees🇩🇪 · S. Endres🇩🇪 · J. Weil🇩🇪 · M. Bleicher🇩🇪

    We calculate dilepton spectra in heavy-ion collisions using a coarse-graining approach to the simulation of the created medium with the UrQMD transport model. This enables the use of dilepton-production rates evaluated in equilibrium quantum-field theory at finite temperatures and chemical potentials.

    Comments:
    4 pages, 2 figures, contribution to the proceedings of "The 15th International Conference on Strangeness in Quark Matter" (SQM 2015), 06-11 July in Dubna, Russia
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
    arXiv:
    1509.05887 [pdf]
    J.Phys.Conf.Ser.(2016)·0 citations
  4. 17

    [Submitted on 21 Sept 2015] (cross-list from hep-ph)

    Electromagnetic triangle anomaly and neutral pion condensation in QCD vacuum

    Gaoqing Cao🇨🇳 · Xu-Guang Huang🇨🇳

    We study the QCD vacuum structure under the influence of an electromagnetic field with a nonzero second Lorentz invariant . We show that the presence of can induce neutral pion () condensation in the QCD vacuum through the electromagnetic triangle anomaly. Within the frameworks of chiral perturbation theory at leading small-momenta expansion as well as the Nambu--Jona-Lasinio model at leading expansion, we quantify the dependence of the condensate on . The stability of the -condensed vacuum against the Schwinger charged pair production due to electric field is also discussed.

    Comments:
    V2: 5 pages, 3 figures, published version
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Lattice (hep-lat); Nuclear Theory (nucl-th)
    arXiv:
    1509.06222 [pdf]
    PLB(2016)·46 citations
  5. 18

    [Submitted on 21 Sept 2015] (cross-list from hep-lat)

    The pion quasiparticle in the low-temperature phase of QCD

    Bastian B. Brandt🇩🇪 · Anthony Francis🇨🇦 · Harvey B. Meyer🇩🇪 · Daniel Robaina🇩🇪

    We investigate the properties of the pion quasiparticle in the low-temperature phase of two-flavor QCD on the lattice with support from chiral effective theory. We find that the pion quasiparticle mass is significantly reduced compared to its value in the vacuum, in contrast to the static screening mass, which increases with temperature. By a simple argument, the two masses are expected to determine the quasiparticle dispersion relation near the chiral limit. Analyzing two-point functions of the axial charge density at non-vanishing spatial momentum, we find that the predicted dispersion relation and the residue of the pion pole are simultaneously consistent with the lattice data at low momentum. The test, based on fits to the correlation functions, is confirmed by a second analysis using the Backus-Gilbert method.

    Comments:
    7 pages, 3 figures, talk presented at the 8th International Workshop on Chiral Dynamics, 29 June - 03 July, 2015 Pisa (Italy)
    Subjects:
    High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
    arXiv:
    1509.06241 [pdf]
    PoS(2016)·1 citation
  6. 19

    [Submitted on 21 Sept 2015] (cross-list from math.CA)

    A Recursive Method for Computing Certain Bessel Function Integrals

    Jeremiah Birrell

    We investigate a family of integrals involving modified Bessel functions that arise in the context of neutrino scattering. Recursive formulas are derived for evaluating these integrals and their asymptotic expansions are computed. We prove in certain cases that the asymptotic expansion yields the exact result after a finite number of terms. In each of these cases we derive a formula that bounds the order at which the expansion terminates. The method of calculation developed in this paper is applicable to similar families of integrals that involve Bessel or modified Bessel functions.

    Comments:
    12 pages
    Subjects:
    math.CA (math.CA); Nuclear Theory (nucl-th)
    arXiv:
    1509.06308 [pdf]
    0 citations
  7. 20

    [Submitted on 21 Sept 2015] (cross-list from nucl-ex)

    Neutrons on a surface of liquid helium

    P. D. Grigoriev · O. Zimmer · T. Ziman · A. D. Grigoriev

    We investigate the possibility of ultracold neutron (UCN) storage in quantum states defined by the combined potentials of the Earth's gravity and the neutron optical repulsion by a horizontal surface of liquid helium. We analyse the stability of the lowest quantum state, which is most susceptible to perturbations due to surface excitations, against scattering by helium atoms in the vapor and by excitations of the liquid, comprised of ripplons, phonons and surfons. This is an unusual scattering problem since the kinetic energy of the neutron parallel to the surface may be much greater than the binding energies perpendicular. The total scattering time constant of these UCNs at 0.7 K is found to exceed one hour, and rapidly increasing with decreasing temperature. Such low scattering rates should enable high-precision measurements of the scheme of discrete energy levels, thus providing improved access to short-range gravity. The system might also be useful for neutron beta-decay experiments. We also sketch new experimental concepts for level population and trapping of UCNs above a flat horizontal mirror.

    Comments:
    18 pages, 3 figures
    Subjects:
    Nuclear Experiment (nucl-ex); cond-mat.other (cond-mat.other); Nuclear Theory (nucl-th)
    arXiv:
    1509.06343 [pdf]
    PRC(2016)·6 citations

Affiliations

first authorsco-authorsvia INSPIRE