4,945 research outputs found

    The exclusive Drell-Yan process and deeply virtual pion production

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    In this talk it is reported on analyses of l p -> l pi+ n and pi- p -> l+ l- n within the handbag approach. It is argued that recent measurements of hard pion production performed by HERMES and CLAS clearly indicate the occurrence of strong contributions from transversely polarized photons. The gamma*T -> pi transitions are described by the transversity GPDs accompanied by twist-3 pion wave functions. The experiments also require strong contributions from the pion pole which can be modeled as a classical one-pion exchange. With these extensions the handbag approach leads to results on cross sections and spin asymmetries in fair agreement with experiment. This approach is also used for an estimate of the partial cross sections for the exclusive Drell-Yan process.Comment: 8 pages, 6 figures, latex with style files jpsj-suppl.cls and cite.sty invited talk presented at MENU2016, Kyoto (Japan), July 2016. arXiv admin note: substantial text overlap with arXiv:1602.0380

    The chirally-odd twist-3 distribution e(x)

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    Properties of the nucleon twist-3 distribution function e(x) are reviewed. It is emphasized that the QCD equations of motion imply the existence of a delta-function at x=0 in e(x), which gives rise to the pion-nucleon sigma-term. According to the resulting ``practical'' DIS sum rules the first and the second moment of e(x) vanish, a situation analogue to that of the pure twist-3 distribution function gˉ2(x)\bar{g}_2(x).Comment: 19 pages, 3 figures, new references and figures adde

    Disorder-driven splitting of the conductance peak at the Dirac point in graphene

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    The electronic properties of a bricklayer model, which shares the same topology as the hexagonal lattice of graphene, are investigated numerically. We study the influence of random magnetic-field disorder in addition to a strong perpendicular magnetic field. We found a disorder-driven splitting of the longitudinal conductance peak within the narrow lowest Landau band near the Dirac point. The energy splitting follows a relation which is proportional to the square root of the magnetic field and linear in the disorder strength. We calculate the scale invariant peaks of the two-terminal conductance and obtain the critical exponents as well as the multifractal properties of the chiral and quantum Hall states. We found approximate values ν2.5\nu\approx 2.5 for the quantum Hall states, but ν=0.33±0.1\nu=0.33\pm 0.1 for the divergence of the correlation length of the chiral state at E=0 in the presence of a strong magnetic field. Within the central n=0n=0 Landau band, the multifractal properties of both the chiral and the split quantum Hall states are the same, showing a parabolic f[α(s)]f[\alpha(s)] distribution with α(0)=2.27±0.02\alpha(0)=2.27\pm 0.02. In the absence of the constant magnetic field, the chiral critical state is determined by α(0)=2.14±0.02\alpha(0)=2.14\pm 0.02

    Sea quark transverse momentum distributions and dynamical chiral symmetry breaking

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    Recent theoretical studies have provided new insight into the intrinsic transverse momentum distributions of valence and sea quarks in the nucleon at a low scale. The valence quark transverse momentum distributions (q - qbar) are governed by the nucleon's inverse hadronic size R^{-1} ~ 0.2 GeV and drop steeply at large p_T. The sea quark distributions (qbar) are in large part generated by non-perturbative chiral-symmetry-breaking interactions and extend up to the scale rho^{-1} ~ 0.6 GeV. These findings have many implications for modeling the initial conditions of perturbative QCD evolution of TMD distributions (starting scale, shape of p_T distributions, coordinate-space correlation functions). The qualitative difference between valence and sea quark intrinsic p_T distributions could be observed experimentally, by comparing the transverse momentum distributions of selected hadrons in semi-inclusive deep-inelastic scattering, or those of dileptons produced in pp and pbar-p scattering.Comment: 9 pages, 5 figures. Proceedings of QCD Evolution Workshop, Jefferson Lab, May 6-10, 201