1,546 research outputs found
Volume dependence of light hadron masses in full lattice QCD
The aim of the GRAL project is to simulate full QCD with standard Wilson
fermions at light quark masses on small to medium-sized lattices and to obtain
infinite-volume results by extrapolation. In order to establish the functional
form of the volume dependence we study systematically the finite-size effects
in the light hadron spectrum. We give an update on the status of the GRAL
project and show that our simulation data for the light hadron masses depend
exponentially on the lattice size.Comment: 3 pages, 1 figure, Lattice2003(spectrum
Vortices on the worldsheet of the QCD string
We investigate the properties of the QCD string in the Euclidean SU(N) pure
gauge theory when the space-time dimensions transverse to it are periodic. From
the point of view of an effective string theory, the string tension
and the low-energy constants of the theory are arbitrary functions of the
sizes of the transverse dimensions L_p. Since the gauge theory is linearly
confining in D=2, 3 and 4 dimensions, we propose an effective string action for
the flux-tube energy levels at any choice of , given and
. The Luscher term only depends on the number of massless bosonic
degrees of freedom and the effective theory can account for its evolution as a
function of . As the size of one transverse dimension is varied, we
predict a Kosterlitz-Thouless transition of the worldsheet field theory at
driven by vortices, after which the periodic
component of the worldsheet displacement vector develops a mass gap and the
effective central charge drops by one unit. The universal properties of the
transition are emphasised.Comment: 18 pages, 1figur
A new simulation algorithm for lattice QCD with dynamical quarks
A previously introduced multi-boson technique for the simulation of QCD with
dynamical quarks is described and some results of first test runs on a
lattice with Wilson quarks and gauge group SU(2) are reported.Comment: 7 pages, postscript file (166 KB
Study of a new simulation algorithm for dynamical quarks on the APE-100 parallel computer
First results on the autocorrelation behaviour of a recently proposed fermion
algorithm by M. L\"uscher are presented and discussed. The occurence of
unexpected large autocorrelation times is explained. Possible improvements are
discussed.Comment: 3 pages, compressed ps-file (uufiles), Contribution to Lattice 9
Two-flavour Schwinger model with dynamical fermions in the L\"uscher formalism
We report preliminary results for 2D massive QED with two flavours of Wilson
fermions, using the Hermitean variant of L\"uscher's bosonization technique.
The chiral condensate and meson masses are obtained. The simplicity of the
model allows for high statistics simulations close to the chiral and continuum
limit, both in the quenched approximation and with dynamical fermions.Comment: Talk presented at LATTICE96(algorithms), 3 pages, 3 Postscript
figures, uses twoside, fleqn, espcrc2, epsf, revised version (details of
approx. polynomial
A Lattice Study of the Glueball Spectrum
Glueball spectrum is studied using an improved gluonic action on asymmetric
lattices in the pure SU(3) gauge theory. The smallest spatial lattice spacing
is about which makes the extrapolation to the continuum limit more
reliable. In particular, attention is paid to the scalar glueball mass which is
known to have problems in the extrapolation. Converting our lattice results to
physical units using the scale set by the static quark potential, we obtain the
following results for the glueball masses: for the
scalar glueball mass and for the tensor glueball.Comment: 10 pages, 2 figures,typos correcte
Locality and Statistical Error Reduction on Correlation Functions
We propose a multilevel Monte-Carlo scheme, applicable to local actions,
which is expected to reduce statistical errors on correlation functions. We
give general arguments to show how the efficiency and parameters of the
algorithm are determined by the low-energy spectrum. As an application, we
measure the euclidean-time correlation of pairs of Wilson loops in SU(3) pure
gauge theory with constant relative errors. In this case the ratio of the new
method's efficiency to the standard one increases as exp{m_0t/2}, where m_0 is
the mass gap and t the time separation.Comment: One paragraph changed in the introduction; some misprints corrected;
12 pages, 6 figure
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
Static forces in d=2+1 SU(N) gauge theories
Using a three-level algorithm we perform a high-precision lattice computation
of the static force up to 1fm in the 2+1 dimensional SU(5) gauge theory.
Discretization errors and the continuum limit are discussed in detail. By
comparison with existing SU(2) and SU(3) data it is found that \sigma
r_0^2=1.65-\pi/24 holds at an accuracy of 1% for all N>=2, where r_0 is the
Sommer reference scale. The effective central charge c_{eff}(r) is obtained and
an intermediate distance r_s is defined via the property c_{eff}(r_s)=\pi/24.
It separates in a natural way the short-distance regime governed by
perturbation theory from the long-distance regime described by an effective
string theory. The ratio r_s/r_0 decreases significantly from SU(2) to SU(3) to
SU(5), where r_s < r_0. We give a preliminary estimate of its value in the
large-N limit. The static force in the smallest representation of N-ality 2,
which tends to the k=2 string tension as r->oo, is also computed up to 0.7fm.
The deviation from Casimir scaling is positive and grows from 0.1% to 1% in
that range.Comment: 25 pages, 8 figures, 11 table
Perturbative calculation of improvement coefficients to O(g^2a) for bilinear quark operators in lattice QCD
We calculate the O(g^2 a) mixing coefficients of bilinear quark operators in
lattice QCD using a standard perturbative evaluation of on-shell Green's
functions. Our results for the plaquette gluon action are in agreement with
those previously obtained with the Schr\"odinger functional method. The
coefficients are also calculated for a class of improved gluon actions having
six-link terms.Comment: 14 pages, REVTe
- …