734 research outputs found
Testing and tuning symplectic integrators for Hybrid Monte Carlo algorithm in lattice QCD
We examine a new 2nd order integrator recently found by Omelyan et al. The
integration error of the new integrator measured in the root mean square of the
energy difference, \bra\Delta H^2\ket^{1/2}, is about 10 times smaller than
that of the standard 2nd order leapfrog (2LF) integrator. As a result, the step
size of the new integrator can be made about three times larger. Taking into
account a factor 2 increase in cost, the new integrator is about 50% more
efficient than the 2LF integrator. Integrating over positions first, then
momenta, is slightly more advantageous than the reverse. Further parameter
tuning is possible. We find that the optimal parameter for the new integrator
is slightly different from the value obtained by Omelyan et al., and depends on
the simulation parameters. This integrator could also be advantageous for the
Trotter-Suzuki decomposition in Quantum Monte Carlo.Comment: 14 pages, 6 figure
Simulation of SU(2) Dynamical Fermion at Finite Chemical Potential and at Finite Temperature
SU(2) lattice gauge theory with dynamical fermion at non-zero chemical
potential and at finite temperature is studied. We focus on the influence of
chemical potential for quark condensate and mass of pseudoscalar meson at
finite temperature.
Hybrid Monte Carlo simulations with staggered fermions are carried
out on lattice. At and
0.05,0.07,0.1, we calculate the quark condensate and masses of
pseudoscalar meson consisting of light and heavier quarks for chemical
potential 0.0,0.02,0.05,0.1,0.2.Comment: Proceedings of the International Workshop on Nonperturbative Methods
and Lattice QCD, Guangzhou, Chin
Scaling in SU(3) theory with a MCRG improved lattice action
We test various improved gauge actions which are made of linear combinations
of Wilson loops. We observe the restoration of rotational symmetry in the
static interquark potential already on coarse lattices as small as 6^3x12.
Furthermore, we study scaling and asymptotic scaling of the string tension with
a MCRG-improved action on 12^3x24 lattices. Preliminary results show that
scaling sets in at a ~ 0.3 fm.Comment: 3 pages, 4 figures, contribution at Lattice '97, Edinburg
Three topics in the Schwinger model
1. We compare Monte Carlo results with analytic predictions for the fermion
condensate, in the massive one-flavour Schwinger model. 2. We illustrate on the
Schwinger model how to facilitate transitions between topological sectors by a
simple reweighting method. 3. We discuss exact, non-perturbative improvement of
the gauge sector.Comment: Three-page contribution to Lat '97 by A.J. van der Sijs. Colourful
typo (IR -> UV) correcte
Renormalization group flow of SU(3) lattice gauge theory - Numerical studies in a two coupling space
We investigate the renormalization group (RG) flow of SU(3) lattice gauge
theory in a two coupling space with couplings and
corresponding to and loops respectively. Extensive
numerical calculations of the RG flow are made in the fourth quadrant of this
coupling space, i.e., and . Swendsen's factor two
blocking and the Schwinger-Dyson method are used to find an effective action
for the blocked gauge field. The resulting renormalization group flow runs
quickly towards an attractive stream which has an approximate line shape. This
is numerical evidence of a renormalized trajectory which locates close to the
two coupling space. A model flow equation which incorporates a marginal
coupling (asymptotic scaling term), an irrelevant coupling and a
non-perturbative attraction towards the strong coupling limit reproduces
qualitatively the observed features. We further examine the scaling properties
of an action which is closer to the attractive stream than the currently used
improved actions. It is found that this action shows excellent restoration of
rotational symmetry even for coarse lattices with fm.Comment: 18 pages with 9 eps figures psfig.sty, typos correcte
Scaling Analysis of Improved Actions for Pure SU(3) Gauge Theory
We have explored the behaviour of some improved actions based on a
nonperturbative renormalization group (RG) analysis in coupling space. We
calculate the RG flow in two-coupling space (\boneone,\bonetwo) and examine
the restoration of rotational invariance and the scaling of physical quantities
.Comment: LATTICE98(improvement
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