3,062 research outputs found

    Neurotransmitter release: Variations on a theme

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    AbstractSimilarities between the ways that synaptic vesicles and large dense-core vesicles release their contents have been emphasized, but recent studies have revealed important mechanistic differences between these two exocytotic processes

    Finite-Volume Scaling of the Quenched Chiral Condensate

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    In the large-volume limit VV\to\infty with V<<1/mπ4V << 1/m_{\pi}^4 the mass-dependent chiral condensate is predicted to satisfy exact finite-volume scaling laws that fall into three major universality classes. We test these analytical predictions with staggered fermions and overlap fermions in gauge field sectors of fixed topological charge ν\nu.Comment: Talk at Lattice99(topology), 3 page

    A study of chiral symmetry in quenched QCD using the Overlap-Dirac operator

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    We compute fermionic observables relevant to the study of chiral symmetry in quenched QCD using the Overlap-Dirac operator for a wide range of the fermion mass. We use analytical results to disentangle the contribution from exact zero modes and simplify our numerical computations. Details concerning the numerical implementation of the Overlap-Dirac operator are presented.Comment: 24 pages revtex with 5 postscript figures included by eps

    Domain Wall Fermions with Exact Chiral Symmetry

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    We show how the standard domain wall action can be simply modified to allow arbitrarily exact chiral symmetry at finite fifth dimensional extent. We note that the method can be used for both quenched and dynamical calculations. We test the method using smooth and thermalized gauge field configurations. We also make comparisons of the performance (cost) of the domain wall operator for spectroscopy compared to other methods such as the overlap-Dirac operator and find both methods are comparable in cost.Comment: revtex, 37 pages, 11 color postscript figure

    Status and Future Perspectives for Lattice Gauge Theory Calculations to the Exascale and Beyond

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    In this and a set of companion whitepapers, the USQCD Collaboration lays out a program of science and computing for lattice gauge theory. These whitepapers describe how calculation using lattice QCD (and other gauge theories) can aid the interpretation of ongoing and upcoming experiments in particle and nuclear physics, as well as inspire new ones.Comment: 44 pages. 1 of USQCD whitepapers

    First Lattice Study of the NN-P11(1440)P_{11}(1440) Transition Form Factors

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    Experiments at Jefferson Laboratory, MIT-Bates, LEGS, Mainz, Bonn, GRAAL, and Spring-8 offer new opportunities to understand in detail how nucleon resonance (NN^*) properties emerge from the nonperturbative aspects of QCD. Preliminary data from CLAS collaboration, which cover a large range of photon virtuality Q2Q^2 show interesting behavior with respect to Q2Q^2 dependence: in the region Q21.5GeV2Q^2 \le 1.5 {GeV}^2, both the transverse amplitude, A1/2(Q2)A_{1/2}(Q^2), and the longitudinal amplitude, S1/2(Q2)S_{1/2}(Q^2), decrease rapidly. In this work, we attempt to use first-principles lattice QCD (for the first time) to provide a model-independent study of the Roper-nucleon transition form factor.Comment: 4 pages, 2 figures, double colum

    Are Topological Charge Fluctuations in QCD Instanton Dominated?

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    We consider a recent proposal by Horv\'ath {\em et al.} to address the question whether topological charge fluctuations in QCD are instanton dominated via the response of fermions using lattice fermions with exact chiral symmetry, the overlap fermions. Considering several volumes and lattice spacings we find strong evidence for chirality of a finite density of low-lying eigenvectors of the overlap-Dirac operator in the regions where these modes are peaked. This result suggests instanton dominance of topological charge fluctuations in quenched QCD.Comment: LaTeX, 15 pages, 8 postscript figures, minor improvements, version to appear in PR
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