arXiv subjects

K. Schilling

Publications and source records attributed to K. Schilling.

At least 91 records · Page 5Linked to original sources

arXiv1996

Dual Superconductor Scenario of Confinement: A Systematic Study of Gribov Copy Effects

We perform a study of the effects from maximal abelian gauge Gribov copies in the context of the dual superconductor scenario of confinement, on the basis of a novel approach for estimation of systematic uncertainties from incomplete gauge fixing. We present numerical results, in SU(2) lattice gauge theory, using the overrelaxed simulated annealing gauge fixing algorithm. We find abelian and non-abelian string tensions to differ significantly, their ratio being 0.92(4) at BETA = 2.5115. An approximate factorization of the abelian potential into monopole and photon contributions has been confirmed, the former giving rise to the abelian string tension.

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arXiv1996

A Parallel SSOR Preconditioner for Lattice QCD

We present a parallelizable SSOR preconditioning scheme for Krylov subspace iterative solvers which proves to be efficient in lattice QCD applications involving Wilson fermions. Our preconditioner is based on a locally lexicographic ordering of the lattice points. In actual hybrid Monte Carlo applications with the bi-conjugate gradient stabilized method BiCGstab, we achieve a gain factor of about 2 in the number of iterations compared to conventional odd-even preconditioning. Whether this translates into similar reductions in run time will depend on the parallel computer in use. We discuss implementation issues using the `Eisenstat-trick' and machine specific advantages of the method for the APE100/Quadrics parallel computer. In a full QCD simulation with Wilson fermions on a 512-processor Quadrics QH4 we find a gain in cpu-time of a factor of 1.7 over odd-even preconditioning for a 24^3 x 40 lattice.

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arXiv1995

Hyper-Systolic Processing on APE100/Quadrics: N^2-Loop Computations

We investigate the performance gains from hyper-systolic implementations of n^2-loop problems on the massively parallel computer Quadrics, exploiting its 3-dimensional interprocessor connectivity. For illustration we study the communication aspects of an exact molecular dynamics simulation of n particles with Coulomb (or gravitational) interactions. We compare the interprocessor communication costs of the standard-systolic and the hyper-systolic approaches for various granularities. We predict gain factors as large as 3 on the Q4 and 8 on the QH4 and measure actual performances on these machine configurations. We conclude that it appears feasable to investigate the thermodynamics of a full gravitating n-body problem with O(10000) particles using the new method on a QH4 system.

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arXiv1995

First Lattice Study of Ghost Propagators in SU(2) and SU(3) Gauge Theories

We present a numerical study of the ghost propagators in Landau gauge for SU(2) and SU(3) gauge theories at $β$=2.7 and $β$=6.0, respectively. Analyzing different lattice sizes up to $32^4$, we find small finite size effects. Down to the smallest available momenta, we observe no evidence for dipole behaviour of the ghost propagators.

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arXiv1995

Semileptonic Decays of D and B Mesons

We report results of our ongoing investigation concerning semileptonic decays of heavy pseudoscalar mesons into pseudoscalar and vector mesons. Particular attention is paid to uncertainties in the $q^2$ and the heavy quark mass dependence of formfactors. Moreover we present a non-perturbative test to the LMK current renormalization scheme for vector current transition matrix elements and find remarkable agreement.

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arXiv1995

QCD with dynamical Wilson fermions - first results from SESAM

First results of a recently started simulation of full QCD with two flavours of sea-quarks at a coupling of $β= 5.6$ on a $16^3 \times 32$ lattice are presented. Emphasis is laid on the statistical significance that can be achieved by an ``integrated luminosity'' of 140 TFlop$\times$hrs, for Hybrid Monte Carlo simulations at four intermediate values of $\frac{m_π}{m_ρ}$. The simulation takes place on the Quadrics QH2 at DESY/Zeuthen and DFG/Bielefeld. The performance is optimized by means of BiCGStab and the chronological inversion method of Brower et al. We discuss the systematic errors arising from lack of the molecular dynamic's reversibility on the 32-bit QH2. For plaquette and meson correlators we find integrated autocorrelation times of $< 20$ units of molecular dynamics time and exponential autocorrelation times of about $50$ units. Using these results we perform preliminary measurements of the central potential and $π$ and $ρ$ correlators on independent configurations and obtain first estimates of the lattice spacings at three values of the dynamical hopping parameter.

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arXiv1995

Exploring Correlation Methods to Determine QCD beta-Functions on the Lattice

We investigate -- as an alternative to usual Monte Carlo Renormalization Group methods -- the feasibility of extracting QCD beta-functions directly from a lattice analysis of correlations between the action and Wilson loops. We test this correlation technique numerically in four dimensional SU(2) gauge theory, on a 16^4 lattice at beta = 2.5 and find very promising results.

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arXiv1995

Weak Decays of Heavy-Light Mesons on the Lattice: Semi-Leptonic Formfactors

We report results (on an intermediate statistics sample) of a study of weak semi-leptonic formfactors of $B$ and $D$ decays, addressing the uncertainties from mass extrapolations to chiral and to heavy quarks. Moreover, we present a nonperturbative test to the LMK current renormalization scheme for vector current {\it transition} matrix elements and find remarkable agreement.

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arXiv1995

Hyper-Systolic Parallel Computing

A new class of parallel algorithms is introduced that can achieve a complexity of O(n^3/2) with respect to the interprocessor communication, in the exact computation of systems with pairwise mutual interactions of all elements. Hitherto, conventional methods exhibit a communicational complexity of O(n^2). The amount of computation operations is not altered for the new algorithm which can be formulated as a kind of h-range problem, known from the mathematical field of Additive Number Theory. We will demonstrate the reduction in communicational expense by comparing the standard-systolic algorithm and the new algorithm on the connection machine CM5 and the CRAY T3D. The parallel method can be useful in various scientific and engineering fields like exact n-body dynamics with long range forces, polymer chains, protein folding or signal processing.

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arXiv1995

Monopoles in Compact U(1) -- Anatomy of the Phase Transition

We present evidence that the existence of a first order phase transition in compact U(1) with Wilson action is not related to monopole loops wrapping around the toroidal lattice, as has been previously suggested. Our analysis is based on the suppression of such loops by `soft boundary conditions' that correspond to an infinitely large chemical potential for the monopoles on the boundary, during the updating process. It is observed that the double peak structure characteristic for the first order phase transition reappears at sufficiently large lattice sizes and separations from the lattice boundary.

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arXiv1995

Semileptonic Decays of Heavy Mesons: A Status Report

We present intermediate results on our ongoing investigation concerning semileptonic decays of heavy pseudoscalar mesons into pseudoscalar and vector mesons. The corresponding formfactors are evaluated at several momenta and appropriate combinations of four light and four heavy quarks, which are chosen to allow for an extrapolation into the B Meson region. In order to obtain clear groundstate signals we apply gauge invariant ``Wuppertal'' smearing to the quarks. The analysis is based on 32 quenched gauge configurations of size $24^3 \times 64$ at $β=6.3$, with Wilson fermions.

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arXiv1995

First-Order Signals in Compact QED with Monopole Suppressed Boundaries

Pure gauge compact QED on hypercubic lattices is considered with periodically closed monopole currents suppressed. We compute observables on sublattices which are nested around the centre of the lattice in order to locate regions where translation symmetry is approximately recovered. Our Monte Carlo simulations on $24^4$-lattices give indications for a first-order nature of the U(1) phase transition.

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arXiv1994

Heavy-light baryonic mass splittings from the lattice

We present lattice estimates of the mass of the heavy-light baryons $Λ_b$ and $Ξ_b$ obtained using propagating heavy quarks. For $Λ_b$ our result is $M_{Λ_b}=5.728 \pm 0.144 \pm 0.018$ GeV, after extrapolation to the continuum limit and in the quenched approximation.

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arXiv1994

Color Flux Profiles in SU(2) Lattice Gauge Theory

Results of a high statistics study of chromo field distributions around static sources in pure SU(2) gauge theory on lattices of volumes $16^4$, $32^4$, and $48^3\times 64$ at $β=2.5$, $2.635$, and $2.74$ are presented. We establish string formation up to physical distances as large as 2 fm.

hep-lat↗

arXiv1994

Spin dependent potentials from SU(2) gauge theory

We present results on spin dependent potentials from lattice simulations of SU(2) gauge theory. The Coulomb like short range part of the central potential is identified as a mixed vector-scalar exchange while the linear long range part is pure scalar.

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arXiv1994

Confining Forces and String Formation from the Lattice

We show the running coupling as derived from the SU(3) QQ potential and discuss preliminary results on spin dependent heavy quark potentials from high statistics lattice simulations of SU(2) gauge theory. The precision suffices to study scaling properties and lattice artifacts (at short distances). We identify the Coulomb like short range interaction as a mixed vector-scalar exchange. We measure flux tube formation between a static QQ pair over physical distances up to 2 fm, with a spatial resolution as small as .05 fm. Consistency with the string picture is found for separation larger than about 1 fm, with a half width of the profile of approximately .7 fm.

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arXiv1994

Observing Long Colour Flux Tubes in SU(2) Lattice Gauge Theory

We present results of a high statistics study of the chromo field distribution between static quarks in SU(2) gauge theory on lattices of volumes 16^4, 32^4, and 48^3*64, with physical extent ranging from 1.3 fm up to 2.7 fm at beta=2.5, beta=2.635, and beta=2.74. We establish string formation over physical distances as large as 2 fm. The results are tested against Michael's sum rules. A detailed investigation of the transverse action and energy flux tube profiles is provided. As a by-product, we obtain the static lattice potential in unpreceded accuracy.

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arXiv1994

Beautiful Baryons from Lattice QCD

We perform a lattice study of heavy baryons, containing one ($Λ_b$) or two $b$-quarks ($Ξ_b$). Using the quenched approximation we obtain for the mass of $Λ_b$ $$ M_{Λ_b}= 5.728 \pm 0.144 \pm 0.018 {\rm GeV}.$$ The mass splitting between the $Λ_b$ and the B-meson is found to increase by about 20\% if the light quark mass is varied from the chiral limit to the strange quark mass.

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