200 research outputs found

    Non-perturbative renormalization constants on the lattice from flavour non-singlet Ward identities

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    By imposing axial and vector Ward identities for flavour-non-singlet currents, we estimate in the quenched approximation the non-perturbative values of combinations of improvement coefficients, which appear in the expansion around the massless case of the renormalization constants of axial, pseudoscalar, vector, scalar non-singlet currents and of the renormalized mass. These coefficients are relevant for the completion of the improvement programme to O(a) of such operators. The simulations are performed with a clover Wilson action non-perturbatively improved.Comment: 9 pages, latex file + 4 eps files of figure

    Non-perturbative running of the average momentum of non-singlet parton densities

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    We determine non-perturbatively the anomalous dimensions of the second moment of non-singlet parton densities from a continuum extrapolation of results computed in quenched lattice simulations at different lattice spacings. We use a Schr\"odinger functional scheme for the definition of the renormalization constant of the relevant twist-2 operator. In the region of renormalized couplings explored, we obtain a good description of our data in terms of a three-loop expression for the anomalous dimensions. The calculation can be used for exploring values of the coupling where a perturbative expansion of the anomalous dimensions is not valid a priori. Moreover, our results provide the non-perturbative renormalization constant that connects hadron matrix elements on the lattice, renormalized at a low scale, with the experimental results, renormalized at much higher energy scales.Comment: Latex2e file, 6 figures, 25 pages, Corrected errors on linear fit in table 2 and discussion on anomalous dimension of f_

    On the extraction of zero momentum form factors on the lattice

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    We propose a method to expand correlation functions with respect to the spatial components of external momenta. From the coefficients of the expansion it is possible to extract Lorentz-invariant form factors at zero spatial momentum transfer avoiding model dependent extrapolations. These objects can be profitably calculated on the lattice. We have explicitly checked the validity of the proposed procedure by considering two-point correlators with insertions of the axial current, the form factors of the semileptonic decay of pseudoscalar mesons, and the hadronic vacuum polarization tensor entering, for example, the lattice calculation of the anomalous magnetic moment of the muon.Comment: 10 pages, 5 figures, published versio

    Evidence for eta prime - pion splitting in unquenched lattice QCD

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    We perform an extrapolation from negative to positive flavour numbers of full QCD lattice estimates of the ηâ€Č\eta' mass. The extrapolations are carried out by keeping ρ\rho and π\pi masses at fixed values. We find an ηâ€Č\eta' -- π\pi splitting which shows a flavour dependence consistent with the Witten Veneziano formula based on the U(1)U(1) anomaly. The quantitative splitting is consistent with the estimates made in the quenched approximation.Comment: 22 pages, uuencoded latex files, text + 8 figure

    The bermions: an approach to lattice QCD dynamical fermions from negative flavour numbers

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    We estimate the effects of dynamical fermions by extrapolating to positive flavour numbers the results from negative values obtained by adding to the pure gauge sector a fermion action where the fields obey a Bose statistics: the bermions.Comment: 21 pages, uuencoded PS file, 11 figures include

    Effects of Nonperturbative Improvement in Quenched Hadron Spectroscopy

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    We discuss a comparative analysis of unimproved and nonperturbatively improved quenched hadron spectroscopy, on a set of 104 gauge configurations, at beta=6.2. We also present here our results for meson decay constants, including the constants f_D and f_Ds in the charm-quark region.Comment: LATTICE98(spectrum

    Non-Perturbatively Improved Quenched Hadron Spectroscopy

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    We make a quenched lattice simulation of hadron spectroscopy at beta=6.2 with the Wilson action non-perturbatively improved. With respect to the unimproved case, the estimate of the lattice spacing is less influenced by the choice of input hadron masses. We study also the effects of using an improved quark mass in the fits to the dependence of hadron masses upon quark masses.Comment: 12 pages, including 5 postscript figure

    Light meson decay constants beyond the quenched approximation

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    We calculate the effects of including dynamical fermion loops in the lattice QCD estimates of meson decay constants, by extrapolating the results from negative flavour numbers after a suitable matching of the pion and rho mass. For moderately light quarks, the values of the decay constants not corrected for the renormalization constants increase with respect to their quenched values.Comment: 9 pages, uuencoded PS file, 2 figures include

    Pseudofermion observables for static heavy meson decay constants on the lattice

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    A method based on the Monte Carlo inversion of the Dirac operator on the lattice provides low noise results for the correlations entering the definition of the heavy meson decay constant in the static limit. The method is complementary to the usual method of smeared sources, avoids the systematic error arising from optimizing the size of the smearing volume and is more efficient for the values of lattice parameters that we have explored.Comment: 11 pages, uuencoded ps file, 2 figures include

    [Chi] and J/[Psi] suppression in heavy ion collisions and a model for its momentum dependence

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    Karsch F, Petronzio R. [Chi] and J/[Psi] suppression in heavy ion collisions and a model for its momentum dependence. Zeitschrift fĂŒr Physik, C: Particles and Fields. 1988;37(4):627-633
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