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Nuclear Theory·nucl-th

Tuesday·February 23, 2016

20 papers—15 primary·5 cross-listed

All20Primary15Cross-lists5
  1. 16

    [Submitted on 21 Feb 2016] (cross-list from cond-mat.quant-gas)

    Dynamic density and spin responses of a superfluid Fermi gas in the BCS-BEC crossover: Path integral formulation and pair fluctuation theory

    Lianyi He

    We present a standard field theoretical derivation of the dynamic density and spin linear response functions of a dilute superfluid Fermi gas in the BCS-BEC crossover in both three and two dimensions. The derivation of the response functions is based on the elegant functional path integral approach which allows us to calculate the density-density and spin-spin correlation functions by introducing the external sources for the density and the spin density. Since the generating functional cannot be evaluated exactly, we consider two gapless approximations which ensure a gapless collective mode (Goldstone mode) in the superfluid state: the BCS-Leggett mean-field theory and the Gaussian-pair-fluctuation (GPF) theory. In the mean-field theory, our results of the response functions agree with the known results from the random phase approximation. We further consider the pair fluctuation effects and establish a theoretical framework for the dynamic responses within the GPF theory. We show that the GPF response theory naturally recover three kinds of famous diagrammatic contributions: the Self-Energy contribution, the Aslamazov-Lakin contribution, and the Maki-Thompson contribution. We also show that unlike the equilibrium state, in evaluating the response functions, the linear (first-order) terms in the external sources as well as the induced order parameter perturbations should be treated carefully. In the superfluid state, there is an additional order parameter contribution which ensures that in the static and long wavelength limit, the density response function recovers the result of the compressibility (compressibility sum rule). We expect that the -sum rule is manifested by the full number equation which includes the contribution from the Gaussian pair fluctuations.

    Comments:
    Published version
    Subjects:
    Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el); Superconductivity (cond-mat.supr-con); Nuclear Theory (nucl-th)
    arXiv:
    1602.06502 [pdf]
    Annals Phys.(2016)·12 citations
  2. 17

    [Submitted on 21 Feb 2016] (cross-list from hep-ph)

    Approximate degeneracy of heavy-light mesons with the same

    Takayuki Matsuki🇯🇵 · Qi-Fang Lü🇨🇳 · Yubing Dong🇨🇳 · Toshiyuki Morii🇯🇵

    Careful observation of the experimental spectra of heavy-light mesons tells us that heavy-light mesons with the same angular momentum are almost degenerate. The estimate is given how much this degeneracy is broken in our relativistic potential model, and it is analytically shown that expectation values of a commutator between the lowest order Hamiltonian and are of the order of with a heavy quark mass . It turns out that nonrelativistic approximation of heavy quark system has a rotational symmetry and hence degeneracy among states with the same . This feature can be tested by measuring higher orbitally and radially excited heavy-light meson spectra for in LHCb and forthcoming BelleII.

    Comments:
    4 pages, 1 table
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Theory (nucl-th)
    arXiv:
    1602.06545 [pdf]
    PLB(2016)·8 citations
  3. 18

    [Submitted on 21 Feb 2016] (cross-list from physics.plasm-ph)

    Nonlinear electromagnetic formulation for particle simulation of lower hybrid waves in toroidal geometry

    J. Bao · Z. Lin · A. Kuley · Z. X. Wang

    Electromagnetic particle simulation model has been formulated and verified for nonlinear processes of lower hybrid (LH) waves in fusion plasmas. Electron dynamics is described by the drift kinetic equation using either kinetic momentum or canonical momentum. Ion dynamics is treated as the fluid system or by the Vlasov equation. Compressible magnetic perturbation is retained to simulate both the fast and slow LH waves. Numerical properties are greatly improved by using electron continuity equation to enforce consistency between electrostatic potential and vector potential, and by using the importance sampling technique. The simulation model has been implemented in the gyrokinetic toroidal code (GTC), and verified for the dispersion relation and nonlinear particle trapping of the electromagnetic LH waves.

    Subjects:
    Plasma Physics (physics.plasm-ph); Nuclear Theory (nucl-th)
    arXiv:
    1602.06554 [pdf]
    Phys.Plasmas(2016)·1 citation
  4. 19

    [Submitted on 22 Feb 2016] (cross-list from hep-ph)

    Electromagnetic spectral properties and Debye screening of a strongly magnetized hot medium

    Aritra Bandyopadhyay🇮🇳 · Chowdhury Aminul Islam🇮🇳 · Munshi G. Mustafa🇮🇳

    We have evaluated the electromagnetic spectral function and its spectral properties by computing the one-loop photon polarization tensor in presence of magnetic field, particularly in a strong field approximation compared to the thermal scale. When the magnetic scale is higher than the thermal scale the lowest Landau level (LLL) becomes effectively (1+1) dimensional strongly correlated system that provides a kinematical threshold based on the mass scale. Beyond this threshold the photon strikes the LLL and the spectral strength starts with a high value due to the dimensional reduction and then falls off with increase of the photon energy due to LLL dynamics in a strong field approximation. This strongly enhances the dilepton rate over the thermal perturbative leading order (Born) rate at very low invariant mass. We have also investigated the electromagnetic screening by computing the Debye screening mass and it depends distinctively on three different scales (mass of the quasiquark, temperature and the magnetic field strength) of a hot magnetized system. The mass dependence of the Debye screening supports the occurrence of a magnetic catalysis effect in the strong field approximation.

    Comments:
    18 pages, 8 figures; Matches with the published version, adjusted for the erratum; Conclusions unchanged
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
    arXiv:
    1602.06769 [pdf]
    PRD(2016)·102 citations
  5. 20

    [Submitted on 22 Feb 2016] (cross-list from nucl-ex)

    Physics case for a polarised target for AFTER@LHC

    J.P. Lansberg · M. Anselmino · R. Arnaldi · S.J. Brodsky · V. Chambert · J.P. Didelez · M.G Echevarria · E.G. Ferreiro · F. Fleuret · Y. Gao · B. Genolini · C. Hadjidakis and 18 other authors

    We review a number of ideas put forward in favour of the use of a polarised target along with the proposed idea of a fixed-target experiment using the LHC beams -- AFTER@LHC. A number of recent studies have shown that single transverse-spin asymmetries (STSAs) are large enough to be precisely measured in the region accessible with AFTER@LHC, in particular as regards the Drell-Yan process as well as single-pion, isolated-photon and jet production. AFTER@LHC with a polarised target would also be the ideal experimental set-up to measure the gluon Sivers effect via a number of original quarkonium STSA studies. We discuss first figures-of-merit based on simulations for AFTER@LHC with a polarised target.

    Comments:
    7 pages, 2 figures, 1 table, LaTeX. Proceedings of the XVIth International Workshop in Polarized Sources, Targets, and Polarimetry, PSTP2015, 14-18 September 2015, Bochum, Germany
    Subjects:
    Nuclear Experiment (nucl-ex); High Energy Physics — Experiment (hep-ex); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
    arXiv:
    1602.06857 [pdf]
    PoS(2016)·18 citations

Affiliations

first authorsco-authorsvia INSPIRE