196 research outputs found

    Nonperturbative Gauge Fixing and Perturbation Theory

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    We compare the gauge-fixing approach proposed by Jona-Lasinio and Parrinello, and by Zwanziger (JPLZ) with the standard Fadeev-Popov procedure, and demonstrate perturbative equality of gauge-invariant quantities, up to irrelevant terms induced by the cutoff. We also show how a set of local, renormalizable Feynman rules can be constructed for the JPLZ procedure.Comment: 9 pages, latex, version to appear in Phys. Rev.

    Current Renormalisation Constants with an O(a)-improved Fermion Action

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    Using chiral Ward identities, we determine the renormalisation constants of bilinear quark operators for the Sheikholeslami-Wohlert action lattice at beta=6.2. The results are obtained with a high degree of accuracy. For the vector current renormalisation constant we obtain Z_V=0.817(2)(8), where the first error is statistical and the second is due to mass dependence of Z_V. This is close to the perturbative value of 0.83. For the axial current renormalisation constant we obtain Z_A = 1.045(+10 -14), significantly higher than the value obtained in perturbation theory. This is shown to reduce the difference between lattice estimates and the experimental values for the pseudoscalar meson decay constants, but a significant discrepancy remains. The ratio of pseudoscalar to scalar renormalisation constants, Z_P/Z_S, is less well determined, but seems to be slightly lower than the perturbative value.Comment: 8 pages uuencoded compressed postscript file. Article to be submitted to Phys.Rev.

    Non-perturbative quark mass renormalization

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    We show that the renormalization factor relating the renormalization group invariant quark masses to the bare quark masses computed in lattice QCD can be determined non-perturbatively. The calculation is based on an extension of a finite-size technique previously employed to compute the running coupling in quenched QCD. As a by-product we obtain the Λ\Lambda--parameter in this theory with completely controlled errors.Comment: Talk given at LATTICE '97, 6 pages, Latex source, 7 eps figures, needs epsfi

    Chiral behaviour of the lattice BKB_K-parameter with the Wilson and Clover Actions at β=6.0\beta = 6.0

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    We present results for the kaon BB-parameter BKB_K from a sample of 200200 configurations using the Wilson action and 460460 configurations using the SW-Clover action, on a 183×6418^3 \times 64 lattice at β=6.0\beta=6.0. We compare results obtained by renormalizing the relevant operator with different ``boosted" values of the strong coupling constant αs\alpha_s. In the case of the SW-Clover action, we also use the operator renormalized non-perturbatively. In the Wilson case, we observe a strong dependence of BKB_K on the prescription adopted for αs\alpha_s, contrary to the results of the Clover case which are almost unaffected by the choice of the coupling. We also find that the matrix element of the operator renormalized non-perturbatively has a better chiral behaviour. This gives us our best estimate of the renormalization group invariant BB-parameter, B^K=0.86±0.15\hat B_K=0.86 \pm 0.15.Comment: LaTeX, 17 pages, 3 postscript figures uuencode

    Weinberg propagator of a free massive particle with an arbitrary spin from the BFV-BRST path integral

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    The transition amplitude is obtained for a free massive particle of arbitrary spin by calculating the path integral in the index-spinor formulation within the BFV-BRST approach. None renormalizations of the path integral measure were applied. The calculation has given the Weinberg propagator written in the index-free form with the use of index spinor. The choice of boundary conditions on the index spinor determines holomorphic or antiholomorphic representation for the canonical description of particle/antiparticle spin.Comment: 31 pages, Latex, version published in Class. Quantum Gra

    Gauge Invariant Smearing and Matrix Correlators using Wilson Fermions at beta=6.2

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    We present an investigation of gauge invariant smearing for Wilson fermions on a 243×4824^3 \times 48 lattice at β=6.2\beta = 6.2. We demonstrate a smearing algorithm that allows a substantial improvement in the determination of the baryon spectrum obtained using propagators smeared at both source and sink, at only a small computational cost. We investigate the matrix of correlators constructed from local and smeared operators, and are able to expose excited states of both the mesons and baryons.Comment: at lattice `92. 4 pages latex + 3 postscript figures. Edinburgh preprint: 92/51

    Lattice Calculation of Heavy-Light Decay Constants with Two Flavors of Dynamical Quarks

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    We present results for fBf_B, fBsf_{B_s}, fDf_D, fDsf_{D_s} and their ratios in the presence of two flavors of light sea quarks (Nf=2N_f=2). We use Wilson light valence quarks and Wilson and static heavy valence quarks; the sea quarks are simulated with staggered fermions. Additional quenched simulations with nonperturbatively improved clover fermions allow us to improve our control of the continuum extrapolation. For our central values the masses of the sea quarks are not extrapolated to the physical uu, dd masses; that is, the central values are "partially quenched." A calculation using "fat-link clover" valence fermions is also discussed but is not included in our final results. We find, for example, fB=190(7)(17+24)(2+11)(0+8)f_B = 190 (7) (^{+24}_{-17}) (^{+11}_{-2}) (^{+8}_{-0}) MeV, fBs/fB=1.16(1)(2)(2)(0+4)f_{B_s}/f_B = 1.16 (1) (2) (2) (^{+4}_{-0}), fDs=241(5)(26+27)(4+9)(0+5)f_{D_s} = 241 (5) (^{+27}_{-26}) (^{+9}_{-4}) (^{+5}_{-0}) MeV, and fB/fDs=0.79(2)(4+5)(3)(0+5)f_{B}/f_{D_s} = 0.79 (2) (^{+5}_{-4}) (3) (^{+5}_{-0}), where in each case the first error is statistical and the remaining three are systematic: the error within the partially quenched Nf=2N_f=2 approximation, the error due to the missing strange sea quark and to partial quenching, and an estimate of the effects of chiral logarithms at small quark mass. The last error, though quite significant in decay constant ratios, appears to be smaller than has been recently suggested by Kronfeld and Ryan, and Yamada. We emphasize, however, that as in other lattice computations to date, the lattice u,du,d quark masses are not very light and chiral log effects may not be fully under control.Comment: Revised version includes an attempt to estimate the effects of chiral logarithms at small quark mass; central values are unchanged but one more systematic error has been added. Sections III E and V D are completely new; some changes for clarity have also been made elsewhere. 82 pages; 32 figure

    Heavy Baryon Specroscopy from the Lattice

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    The results of an exploratory lattice study of heavy baryon spectroscopy are presented. We have computed the full spectrum of the eight baryons containing a single heavy quark, on a 243×4824^3\times 48 lattice at β=6.2\beta=6.2, using an O(a)O(a)-improved fermion action. We discuss the lattice baryon operators and give a method for isolating the contributions of the spin doublets (Σ,Σ)(\Sigma,\Sigma^*), (Ξ,Ξ)(\Xi',\Xi^*) and (Ω,Ω)(\Omega,\Omega^*) to the correlation function of the relevant operator. We compare our results with the available experimental data and find good agreement in both the charm and the beauty sectors, despite the long extrapolation in the heavy quark mass needed in the latter case. We also predict the masses of several undiscovered baryons. We compute the \Lambda-\mbox{pseudoscalar meson} and ΣΛ\Sigma-\Lambda mass splittings. Our results, which have errors in the range 1030% 10-30\%, are in good agreement with the experimental numbers. For the ΣΣ\Sigma^*-\Sigma mass splitting, we find results considerably smaller than the experimental values for both the charm and the beauty baryons, although in the latter case the experimental results are still preliminary. This is also the case for the lattice results for the hyperfine splitting for the heavy mesons.Comment: 31 pages LaTex, with postscript figures include
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