1,946 research outputs found

    Instanton-Induced Correlations in Hadrons

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    QCD instantons generate non-perturbative spin- and flavor- dependent forces between quarks. We review the results of a series of studies on instanton-induced correlations in hadrons. We first present some evidence for instanton-mediated interactions in QCD, based on lattice simulations. Then we show that the Instanton Liquid Model can reproduce the available data on proton and pion form factors at large momentum transfer and explain the delay of the onset of the perturbative regime in several hard reactions. We also show that instantons generate a deeply bound scalar color anti-triplet diquark, with a mass of about 450 MeV and size comparable with that of the proton. The strong attraction in the anti-triplet scalar diquark channel leads to a quantitative description of non-leptonic weak decays of hyperons and provides a microscopic dynamical explanation of the Delta I=1/2 rule.Comment: Summary of the results presented at the "8th Workshop on Non-perturbative Quantum Chromodynamics", Paris 7-11 June 2003, the "26th International School on Nuclear Physics", Erice 16-24 September 2004, and the "X Convegno sui Problemi della Fisica Nucleare Teorica", Cortona, 6-9 October 200

    Molecular Dynamics at Low Time Resolution

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    The internal dynamics of macro-molecular systems is characterized by widely separated time scales, ranging from fraction of ps to ns. In ordinary molecular dynamics simulations, the elementary time step dt used to integrate the equation of motion needs to be chosen much smaller of the shortest time scale, in order not to cut-off important physical effects. We show that, in systems obeying the over-damped Langevin Eq., the fast molecular dynamics which occurs at time scales smaller than dt can be analytically integrated out and gives raise to a time-dependent correction to the diffusion coefficient, which we rigorously compute. The resulting effective Langevin equation describes by construction the same long-time dynamics, but has a lower time resolution power, hence it can be integrated using larger time steps dt. We illustrate and validate this method by studying the diffusion of a point-particle in a one-dimensional toy-model and the denaturation of a protein.Comment: 12 pages, 5 figure

    Rotation-invariant relations in vector meson decays into fermion pairs

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    The rotational properties of angular momentum eigenstates imply the existence of a frame-independent relation among the parameters of the decay distribution of vector mesons into fermions. This relation is a generalization of the Lam-Tung identity, a result specific to Drell-Yan production in perturbative QCD, here shown to be equivalent to the dynamical condition that the dilepton always originates from a transversely polarized photon
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