16,328 research outputs found

    Hydrodynamic limit of a disordered lattice gas

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    We consider a model of lattice gas dynamics in the d-dimensional cubic lattice in the presence of disorder. If the particle interaction is only mutual exclusion and if the disorder field is given by i.i.d. bounded random variables, we prove the almost sure existence of the hydrodynamical limit in dimension d>2. The limit equation is a non linear diffusion equation with diffusion matrix characterized by a variational principle

    Results from a Non-Perturbative Renormalization of Lattice Operators

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    We propose a general renormalization method, which avoids completely the use of lattice perturbation theory. We present the results from its numerical applications to two-fermion operators on a 163×3216^3 \times 32 lattice, at ÎČ=6.0\beta=6.0.Comment: 3 pages postscript file. Contribution to Lattice '9

    Non-perturbative renormalization in kaon decays

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    We discuss the application of the MPSTV non-perturbative method \cite{NPM} to the operators relevant to kaon decays. This enables us to reappraise the long-standing question of the ΔI=1/2\Delta I=1/2 rule, which involves power-divergent subtractions that cannot be evaluated in perturbation theory. We also study the mixing with dimension-six operators and discuss its implications to the chiral behaviour of the BKB_K parameter.Comment: Talk presented at LATTICE96(improvement), LaTeX 3 pages, uses espcrc2, 2 postscript figure

    Lattice computation of structure functions

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    Recent lattice calculations of hadron structure functions are described.Comment: Plenary talk presented at LATTICE96, LaTeX, 7 pages, 5 figures, espcrc2.sty and epsfig.sty include

    Non-perturbative Renormalization of Lattice Operators

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    We briefly review and compare three methods (one perturbative, one based on Ward Identities and one non-perturbative) for the calculation of the renormalization constants of lattice operators. The following results are presented: (a) non perturbative renormalization of the operators with light quarks; (b) the renormalization constants with a heavy (charm) quark mass and its KLM improvement; (c) the non perturbative determination of the mixing of the ΔS=2\Delta S = 2 operator.Comment: 9 pages, uuencoded PS file, 8 figures included, 1 tabl

    A possible theoretical explanation of metallicity gradients in elliptical galaxies

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    Models of chemical evolution of elliptical galaxies taking into account different escape velocities at different galactocentric radii are presented. As a consequence of this, the chemical evolution develops differently in different galactic regions; in particular, we find that the galactic wind, powered by supernovae (of type II and I) starts, under suitable conditions, in the outer regions and successively develops in the central ones. The rate of star formation (SFR) is assumed to stop after the onset of the galactic wind in each region. The main result found in the present work is that this mechanism is able to reproduce metallicity gradients, namely the gradients in the Mg2Mg_2 index, in good agreement with observational data. We also find that in order to honor the constant [Mg/Fe] ratio with galactocentric distance, as inferred from metallicity indices, a variable initial mass function as a function of galactocentric distance is required. This is only a suggestion since trends on abundances inferred just from metallicity indices are still uncertain.Comment: 18 pages, LaTeX file with 4 figures using mn.sty, submitted to MNRA

    The phase diagrams of iron-based superconductors: theory and experiments

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    Phase diagrams play a primary role in the understanding of materials properties. For iron-based superconductors (Fe-SC), the correct definition of their phase diagrams is crucial because of the close interplay between their crystallo-chemical and magnetic properties, on one side, and the possible coexistence of magnetism and superconductivity, on the other. The two most difficult issues for understanding the Fe-SC phase diagrams are: 1) the origin of the structural transformation taking place during cooling and its relationship with magnetism; 2) the correct description of the region where a crossover between the magnetic and superconducting electronic ground states takes place. Hence a proper and accurate definition of the structural, magnetic and electronic phase boundaries provides an extremely powerful tool for material scientists. For this reason, an exact definition of the thermodynamic phase fields characterizing the different structural and physical properties involved is needed, although it is not easy to obtain in many cases. Moreover, physical properties can often be strongly dependent on the occurrence of micro-structural and other local-scale features (lattice micro-strain, chemical fluctuations, domain walls, grain boundaries, defects), which, as a rule, are not described in a structural phase diagram. In this review, we critically summarize the results for the most studied 11-, 122- and 1111-type compound systems, providing a correlation between experimental evidence and theory

    DEPENDENCE OF THE CURRENT RENORMALISATION CONSTANTS ON THE QUARK MASS

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    We study the behaviour of the vector and axial current renormalisation constants ZVZ_V and ZAZ_A as a function of the quark mass, mqm_q. We show that sizeable O(amq)O(am_q) and O(g02amq)O(g_0^2 a m_q) systematic effects are present in the Wilson and Clover cases respectively. We find that the prescription of Kronfeld, Lepage and Mackenzie for correcting these artefacts is not always successful.Comment: Contribution to Lattice'94, 3 pages PostScript, uuencoded compressed

    Short note on magnetic impurities in SmFeAsO1−x_{1-x}Fx_x (x=0, 0.07) compounds revealed by zero-field 75^{75}As NMR

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    We have performed zero-field 75^{75}As nuclear magnetic resonance study of SmFeAsO1−x_{1-x}Fx_x (x=0, 0.07) polycrystals in a wide frequency range at various temperatures. 75^{75}As resonance line was found at around 265 MHz revealing the formation of the intermetallic FeAs clusters in the new layered superconductors. We have also demonstrated that NMR is a sensitive tool for probing the quality of these materials.Comment: Revised authorshi
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