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Nuclear Theory·nucl-th

Tuesday·March 24, 2015

6 papers—2 primary·4 cross-listed

All6Primary2Cross-lists4
  1. 03

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

    Chiral Corrections to Nucleon Two- and Three-Point Correlation Functions

    Brian C. Tiburzi🇺🇸

    We consider multi-particle contributions to nucleon two- and three-point functions from the perspective of chiral dynamics. Lattice nucleon interpolating operators, which have definite chiral transformation properties, can be mapped into chiral perturbation theory. Using the most common of such operators, we determine pion-nucleon and pion-delta couplings to nucleon two- and three-point correlation functions at leading order in the low-energy expansion. The couplings of pions to nucleons and deltas in two-point functions are consistent with simple phase-space considerations, in accordance with the Lehmann spectral representation. An argument based on available phase space on a torus is utilized to derive the scaling of multiple-pion couplings. While multi-pion states are indeed suppressed, this suppression scales differently with particle number compared to that in infinite volume. For nucleon three-point correlation functions, we investigate the axial-vector current at vanishing momentum transfer. The effect of pion-nucleon and pion-delta states on the extraction of the nucleon axial charge is assessed. We show that couplings to finite volume multi-particle states could potentially lead to overestimation of the axial charge. Hence pion-nucleon excited states cannot explain the trend seen in lattice QCD calculations of the nucleon axial charge.

    Comments:
    18 pages, 3 figures, v.2 comparison with arXiv:1503.03649 added, v.3 phase-space argument corrected
    Subjects:
    High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
    arXiv:
    1503.06329 [pdf]
    PRD(2015)·32 citations
  2. 04

    [Submitted on 23 Mar 2015] (cross-list from hep-ph)

    -wave interaction in a finite volume and the

    Li-Sheng Geng🇨🇳 · Xiu-Lei Ren🇨🇳 · Yu Zhou🇨🇳 · Hua-Xing Chen🇨🇳 · Eulogio Oset🇪🇸

    Lattice QCD simulations provide a promising way to disentangle different interpretations of hadronic resonances, which might be of particular relevance to understand the nature of the so-called particles. Recent studies have shown that in addition to the well-established naive quark model picture, the axial-vector meson can also be understood as a dynamically generated state built upon the interaction. In this work, we calculate the energy levels of the system in the channel in finite volume using the chiral unitary approach. We propose to calculate the loop function in the dimensional regularization scheme, which is equivalent to the hybrid approach adopted in previous studies. We also study the inverse problem of extracting the bound state information from synthetic lattice QCD data and comment on the difference between our approach and the Lüscher method.

    Comments:
    Discussions about partial wave mixing and coupled channel effects added; to appear in Physical Review D
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Lattice (hep-lat); Nuclear Theory (nucl-th)
    arXiv:
    1503.06633 [pdf]
    PRD(2015)·28 citations
  3. 05

    [Submitted on 23 Mar 2015] (cross-list from hep-ph)

    On the Extraction of Cross Sections for pi0 and eta Photoproduction off Neutrons from Deuteron Data

    V. E. Tarasov (ITEP)🇷🇺 · W. J. Briscoe (GW)🇺🇸 · M. Dieterle (Basel U.)🇨🇭 · B. Krusche (Basel U.)🇨🇭 · A. E. Kudryavtsev (ITEP/GW)🇷🇺 · M. Ostrick (JGU)🇩🇪 · I. I. Strakovsky (GW)🇺🇸

    We discuss the procedure of extracting the photoproduction cross section for neutral pseudoscalar mesons off neutrons from deuteron data. The main statement is that the final-state interaction (FSI) corrections for the proton and neutron target are in general not equal, but for pi0 production there are special cases were they have to be identical and there are large regions in the parameter space of incident photon energy and pion polar angle, \theta^*, where they happen to be quite similar. The corrections for both target nucleons are practically identical for production in the energy range of the Delta(1232)3/2+ resonance due to the specific isospin structure of this excitation. Also above the -isobar range large differences between proton and neutron correction factors are only predicted for extreme forward angles ( < 20 deg), but the results are similar for larger angles. Numerical results for the gp-->pi0p and gn-->pi0n correction factors are discussed. Also the model description for the available data on the differential gd-->pi0pn cross sections are given.

    Comments:
    16 pages, 5 figures; v2 fixed several minor typos
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
    arXiv:
    1503.06671 [pdf]
    Phys.Atom.Nucl.(2016)·25 citations
  4. 06

    [Submitted on 23 Mar 2015] (cross-list from cond-mat.mes-hall)

    Resonance width distribution in RMT: Weak coupling regime beyond Porter-Thomas

    Yan V. Fyodorov · Dmitry V. Savin

    We employ the random matrix theory (RMT) framework to revisit the distribution of resonance widths in quantum chaotic systems weakly coupled to the continuum via a finite number M of open channels. In contrast to the standard first-order perturbation theory treatment we do not a priory assume the resonance widths being small compared to the mean level spacing. We show that to the leading order in weak coupling the perturbative distribution of the resonance widths (in particular, the Porter-Thomas distribution at M=1) should be corrected by a factor related to a certain average of the ratio of square roots of the characteristic polynomial ("spectral determinant") of the underlying RMT Hamiltonian. A simple single-channel expression is obtained that properly approximates the width distribution also at large resonance overlap, where the Porter-Thomas result is no longer applicable.

    Comments:
    6 pages, 1 figure (minor corrections, typos fixed)
    Subjects:
    Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Mathematical Physics (math-ph); math.MP (math.MP); nlin.CD (nlin.CD); Nuclear Theory (nucl-th)
    arXiv:
    1503.06787 [pdf]
    EPL(2015)·16 citations

Affiliations

first authorsco-authorsvia INSPIRE