66,081 research outputs found
Gauge action improvement and smearing
The effect of repeatedly smearing SU(3) gauge configurations is investigated.
Six gauge actions (Wilson, Symanzik, Iwasaki, DBW2, Beinlich-Karsch-Laermann,
Langfeld; combined with a direct SU(3)-overrelaxation step) and three smearings
(APE, HYP, EXP) are compared. The impact on large Wilson loops is monitored,
confirming the signal-to-noise prediction by Lepage. The fat-link definition of
the ``naive'' topological charge proves most useful on improved action
ensembles.Comment: 24 pages, 12 figures; v2: several new Ref
Scaling study of an improved fermion action on quenched lattices
We present scaling studies for heavy-quark observables calculated with an
-improved fermion action on tree-level Symanzik improved gauge
configurations. Lattices of 2.0-3.8 GeV with an equal physical volume
1.6 fm are used. The results are compared with the standard domain-wall and
naive Wilson fermions.Comment: 7 pages, 3 figures, presented at the 32nd International Symposium on
Lattice Field Theory, 23-28 June, 2014, Colombia University, New York, US
Moments of Nucleon Light Cone Quark Distributions Calculated in Full Lattice QCD
Moments of the quark density, helicity, and transversity distributions are
calculated in unquenched lattice QCD. Calculations of proton matrix elements of
operators corresponding to these moments through the operator product expansion
have been performed on lattices for Wilson fermions at using configurations from the SESAM collaboration and at
using configurations from SCRI. One-loop perturbative renormalization
corrections are included. At quark masses accessible in present calculations,
there is no statistically significant difference between quenched and full QCD
results, indicating that the contributions of quark-antiquark excitations from
the Dirac Sea are small. Close agreement between calculations with cooled
configurations containing essentially only instantons and the full gluon
configurations indicates that quark zero modes associated with instantons play
a dominant role. Naive linear extrapolation of the full QCD calculation to the
physical pion mass yields results inconsistent with experiment. Extrapolation
to the chiral limit including the physics of the pion cloud can resolve this
discrepancy and the requirements for a definitive chiral extrapolation are
described.Comment: 53 Pages Revtex, 26 Figures, 9 Tables. Added additional reference and
updated referenced data in Table I
Four-quark stability
The physics of charm has become one of the best laboratories exposing the
limitations of the naive constituent quark model and also giving hints into a
more mature description of meson spectroscopy, beyond the simple
quark--antiquark configurations. In this talk we review some recent studies of
multiquark components in the charm sector and discuss in particular exotic and
non-exotic four-quark systems, both with pairwise and many-body forces.Comment: 6 pages. Article based on the presentations by J. Vijande and J.-M.
Richard at the Fifth Workshop on Critical Stability, Erice, Sicil
About local configurations in arithmetic planes
AbstractIn Vittone and Chassery (Proc. of DGCI’97, Vol. 1347 of Lecture Notes in Computer Sciences, 1997, pp. 87–98) J.-M. Chassery and J. Vittone studied local configurations of (m,n)-cubes in naive planes in function of the parameters of these naive planes. More precisely, they enumerated the bicubes and the tricubes that appear in a naive hyperplane of parameters (a,b,c). A symmetry about the line c=a+b appears clearly in this enumeration. The aim of this paper is to prove that the configurations of (n×n)-cubes in the plane of parameters (a,b,c) are in one-to-one relation with those in the plane of parameters (c-b, c-a,c). If we restrict the parameters to the planes such that a+b⩽c, we note a second symmetry about the line c=2b; We also prove this symmetry. We generalize a theorem established by Réveilles and Gérard (Gérard, Proc. of DGCI’99, Vol. 1568 of Lecture Notes in Computer Sciences, 1999, pp. 65–75, Reveilles, Vision Geometry 4, Vol. 2573 of SPIE 95, San Diego, 1995) and these symmetries to the local configurations of planes of given thickness
Discrete theta angle from an O5-plane
We consider 5d gauge theory based on a brane
configuration with an O5-plane. At the UV fixed point, the theory with no
matter enjoys enhanced global symmetry or depending on the
discrete theta angle (mod ). A naive brane configuration
with an O5-plane, however, does not distinguish two different theories, as it
describes the weak coupling region. We devise a technique for computing 5d
Seiberg-Witten curve of the two theories from the brane web with an O5-plane.
Their Seiberg-Witten curves show that their M5 configurations under the
presence of OM5-planes are different. The decompactification limit of each
Seiberg-Witten curve also shows distinct phase structures in their Coulomb
branch leading to significantly different 5-brane configurations with
an O5-plane in the strong coupling region.Comment: v1: 45 pages, 36 figures, v2: published version, v3: a typo correcte
Heavy-light mesons with staggered light quarks
We demonstrate the viability of improved staggered light quarks in studies of
heavy-light systems. Our method for constructing heavy-light operators exploits
the close relation between naive and staggered fermions. The new approach is
tested on quenched configurations using several staggered actionsn combined
with nonrelativistic heavy quarks. The B_s meson kinetic mass, the hyperfine
and 1P-1S splittings in B_s, and the decay constant f_{B_s} are calculated and
compared to previous quenched lattice studies. An important technical detail,
Bayesian curve-fitting, is discussed at length.Comment: 38 pages, figures included. v2: Entry in Table IX corrected and other
minor changes, version appearing in Phys. Rev.
Topology without cooling: instantons and monopoles near to deconfinement
In an attempt to describe the change of topological structure of pure SU(2)
gauge theory near deconfinement a renormalization group inspired method is
tested. Instead of cooling, blocking and subsequent inverse blocking is applied
to Monte Carlo configurations to capture topological features at a well-defined
scale. We check that this procedure largely conserves long range physics like
string tension. UV fluctuations and lattice artefacts are removed which
otherwise spoil topological charge density and Abelian monopole currents. We
report the behaviour of topological susceptibility and monopole current
densities across the deconfinement transition and relate the two faces of
topology to each other. First results of a cluster analysis are described.Comment: 6 pages, 8 figures, LaTeX with espcrc2.sty. Talk and poster presented
at Lattice97, Edinburgh, 22-26 July 1997, to appear in Nucl. Phys. B
(Proc.Suppl.
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