2,928 research outputs found
Non-perturbative O(a) improvement of the vector current
We discuss non-perturbative improvement of the vector current, using the
Schroedinger Functional formalism. By considering a suitable Ward identity, we
compute the improvement coefficient which gives the O(a) mixing of the tensor
current with the vector one.Comment: 3 pages (LaTeX, 2 ps figures, styles), talk presented at Lattice 9
Universal behaviour of the SU(2) running coupling constant in the continuum limit
We present data from the ALPHA Collaboration about lattice calculation of
SU(2) pure--gauge running coupling constant, obtained with two different
definitions of the coupling itself, which show universality of the continuum
limit and clarify the applicability of renormalized perturbation theory.Comment: 3 pages, postscript, contribution to LAT94 also available at
http://sutova.roma2.infn.it/preprints/TovApe/lat94m.ps (eq. (3) corrected
A perturbative determination of O(a) boundary improvement coefficients for the Schr\"odinger Functional coupling at 1-loop with improved gauge actions
We determine O() boundary improvement coefficients up to 1-loop level for
the Schr\"odinger Functional coupling with improved gauge actions including
plaquette and rectangle loops. These coefficients are required to implement
1-loop O() improvement in full QCD simulations for the coupling with the
improved gauge actions. To this order, lattice artifacts of step scaling
function for each improved gauge action are also investigated. In addition,
passing through the SF scheme, we estimate the ratio of -parameters
between the improved gauge actions and the plaquette action more accurately.Comment: 17 pages, 2 figures, 6 table
Lattice QCD without topology barriers
As the continuum limit is approached, lattice QCD simulations tend to get
trapped in the topological charge sectors of field space and may consequently
give biased results in practice. We propose to bypass this problem by imposing
open (Neumann) boundary conditions on the gauge field in the time direction.
The topological charge can then flow in and out of the lattice, while many
properties of the theory (the hadron spectrum, for example) are not affected.
Extensive simulations of the SU(3) gauge theory, using the HMC and the closely
related SMD algorithm, confirm the absence of topology barriers if these
boundary conditions are chosen. Moreover, the calculated autocorrelation times
are found to scale approximately like the square of the inverse lattice
spacing, thus supporting the conjecture that the HMC algorithm is in the
universality class of the Langevin equation.Comment: Plain TeX source, 26 pages, 4 figures include
Center vortex model for the infrared sector of SU(3) Yang-Mills theory -- baryonic potential
The baryonic potential in the framework of the SU(3) random vortex
world-surface model is evaluated for a variety of static color source
geometries. For comparison, carefully taking into consideration the string
tension anisotropy engendered by the hypercubic lattice description, also the
Delta and Y law predictions for the baryonic potential are given. Only the Y
law predictions are consistent with the baryonic potentials measured.Comment: 13 LaTeX pages, 2 figures (3 ps files). Replacement contains
additional reference
The gradient flow running coupling with twisted boundary conditions
We study the gradient flow for Yang-Mills theories with twisted boundary
conditions. The perturbative behavior of the energy density is used to define a running coupling at a scale given by the
linear size of the finite volume box. We compute the non-perturbative running
of the pure gauge coupling constant and conclude that the technique is
well suited for further applications due to the relatively mild cutoff effects
of the step scaling function and the high numerical precision that can be
achieved in lattice simulations. We also comment on the inclusion of matter
fields.Comment: 27 pages. LaTe
Non-perturbative improvement of composite operators with Wilson fermions
We propose a method to improve lattice operators composed of Wilson fermions
which allows the removal of all corrections of , including those
proportional to the quark mass, leaving only errors of . The method
exploits the fact that chiral symmetry is restored at short distances. By
imposing this requirement on correlation functions of improved lattice
operators at short distances, the coefficients which appear in these operators
can be determined. The method is an extension of the improvement program of the
ALPHA collaboration, which, up to now, has only been applicable in the chiral
limit. The extension to quarks with non-zero masses is particularly important
for applications in heavy quark physics.Comment: 15 pages, Late
Quark confinement and the bosonic string
Using a new type of simulation algorithm for the standard SU(3) lattice gauge
theory that yields results with unprecedented precision, we confirm the
presence of a correction to the static quark potential at large
distances , with a coefficient as predicted by the bosonic string
theory. In both three and four dimensions, the transition from perturbative to
string behaviour is evident from the data and takes place at surprisingly small
distances.Comment: TeX source, 21 pages, figures include
QCD with light Wilson quarks on fine lattices (I): first experiences and physics results
Recent conceptual, algorithmic and technical advances allow numerical
simulations of lattice QCD with Wilson quarks to be performed at significantly
smaller quark masses than was possible before. Here we report on simulations of
two-flavour QCD at sea-quark masses from slightly above to approximately 1/4 of
the strange-quark mass, on lattices with up to 64x32^3 points and spacings from
0.05 to 0.08 fm. Physical sea-quark effects are clearly seen on these lattices,
while the lattice effects appear to be quite small, even without O(a)
improvement. A striking result is that the dependence of the pion mass on the
sea-quark mass is accurately described by leading-order chiral perturbation
theory up to meson masses of about 500 MeV.Comment: TeX source, 17 pages, figures include
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