62 research outputs found
The contribution of O(alpha) radiative corrections to the renormalised anisotropy and application to general tadpole improvement schemes: addendum to "One loop calculation of the renormalised anisotropy for improved anisotropic gluon actions on a lattice" [hep-lat/0208010]
General O(alpha) radiative corrections to lattice actions may be interpreted
as counterterms that give additive contributions to the one-loop
renormalisation of the anisotropy. The effect of changing the radiative
coefficients is thus easily calculable. In particular, the results obtained in
a previous paper for Landau mean link improved actions apply in any tadpole
improvement scheme. We explain how this method can be exploited when tuning
radiatively improved actions. Efficient methods for self-consistently tuning
tadpole improvement factors are also discussed.Comment: 3 pages of revte
Improved Langevin Methods for Spin Systems
We investigate methods for variance reduction and the elimination of
systematic error in a Fourier accelerated Langevin scheme for general spin
models. We present results for the model in
two-dimensions that are consistent wit h those from multi-grid methods. We
argue that the timing for the Langevin method makes it comparable to multi-grid
for a given level of error.Comment: 16, DAMTP-92-7
NRQCD on an anisotropic lattice
We present preliminary results for the Upsilon spectrum on an anisotropic
lattice using the improved O(mv^6) NRQCD Hamiltonian. We find accurate results
can be obtained in moderate computer times and that they agree with earlier
results on an isotropic lattice.Comment: 3 pages, LATEX2e, talk presented at LATTICE '98 by R.R. Horgan, uses
styles[espcrc2,epsfig
String Breaking in Quenched QCD
We present preliminary quenched results on a new operator for the
investigation of string-breaking within SU(2)-colour QCD. The ground-state of a
spatially-separated static-light meson-antimeson pair is a combination of a
state with two distinct mesons, expected to dominate for large separations, and
a state where the light-quarks have annihilated, which contributes for short
distances. The crossover between these two regimes provides a measure of the
string-breaking scale length.Comment: LATTICE98(confine), 3 pages, 4 figure
Hybrid Quarkonia with High Statistics from NRQCD
We have studied the O(mv^6) effects in NRQCD on the spectrum of heavy
quarkonia and compare our results for different lattices (quenched and
dynamical). We also report on an investigation into hybrid states within the
framework of NRQCD. This suggests that the lowest lying hybrid is around the
B^* \bar B threshold and 3 standard deviations above the B \bar B.Comment: 3 pages, LaTeX2e, 4 figures, uses styles [espcrc2, epsf], talk
presented at Lattice 9
Lattice perturbation theory for gluonic and fermionic actions
We calculate the two loop Landau mean links and the one loop renormalisation
of the anisotropy for Wilson and improved SU(3) gauge actions, using twisted
boundary conditions as a gauge invariant infrared regulator. We show these
accurately describe simulated results, and outline a method for generating
Feynman rules for general lattice field theories, in a form suitable for
efficient numerical calculation of perturbative loop diagrams.Comment: 6 pages of LaTeX. Two posters at Lattice2002(improve) combine
QCD Pressure and the Trace Anomaly
Exact relations between the QCD thermal pressure and the trace anomaly are
derived. These are used, first, to prove the equivalence of the thermodynamic
and the hydrodynamic pressure in equilibrium in the presence of the trace
anomaly, closing a gap in previous arguments. Second, in the temporal axial
gauge a formula is derived which expresses the thermal pressure in terms of a
Dyson-resummed two-point function. This overcomes the infrared problems
encountered in the conventional perturbation-theory approach.Comment: 9 pages plain te
Perturbation theory vs. simulation for tadpole improvement factors in pure gauge theories
We calculate the mean link in Landau gauge for Wilson and improved SU(3)
anisotropic gauge actions, using two loop perturbation theory and Monte Carlo
simulation employing an accelerated Langevin algorithm. Twisted boundary
conditions are employed, with a twist in all four lattice directions
considerably improving the (Fourier accelerated) convergence to an improved
lattice Landau gauge. Two loop perturbation theory is seen to predict the mean
link extremely well even into the region of commonly simulated gauge couplings
and so can be used remove the need for numerical tuning of self-consistent
tadpole improvement factors. A three loop perturbative coefficient is inferred
from the simulations and is found to be small. We show that finite size effects
are small and argue likewise for (lattice) Gribov copies and double Dirac
sheets.Comment: 13 pages of revtex
Conformal Anomaly for Free Scalar Propagation on Curved Bounded Manifolds
The trace anomaly for free propagation in the context of a conformally
invariant scalar field theory defined on a curved manifold of positive constant
curvature with boundary is evaluated through use of an asymptotic heat kernel
expansion. In addition to their direct physical significance the results are
also of relevance to the holographic principle and to Quantum Cosmology.Comment: 8 pages. To appear in General Relativity and Gravitatio
Radial Excited States for Heavy Quark Systems in NRQCD
Following the Non-Relativistic QCD approach we use a gauge invariant smearing
method with factorization to measure the excitation energies for a heavy
system on a lattice at . The results come
from averaging over an ensemble of 60 QCD configurations. In order to enhance
the signal from each configuration we use wall sources for quark propagators.
The quark Hamiltonian contains only the simplest non-relativistic kinetic
energy term. The results are listed for a range of bare quark masses. The mass
splittings are insensitive to this variable though there are a slight trends
with increasing quark mass. For an appropriate choice of UV cut-off
(Gev) the mass spectrum compares reasonably well with the
experimental values for the spin-averaged energy gaps of the system.
We also present results for the and waves for the lowest bare quark
mass. The results are consistent with degeneracy between the two types of
wave. This encourages the idea that even with our simple quark Hamiltonian the
departure from rotational invariance is not great.Comment: 12 page
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