107 research outputs found
Perfect Lattice Perturbation Theory: A Study of the Anharmonic Oscillator
As an application of perfect lattice perturbation theory, we construct an
O(\lambda) perfect lattice action for the anharmonic oscillator analytically in
momentum space. In coordinate space we obtain a set of 2-spin and 4-spin
couplings \propto \lambda, which we evaluate for various masses. These
couplings never involve variables separated by more than two lattice spacings.
The O(\lambda) perfect action is simulated and compared to the standard action.
We discuss the improvement for the first two energy gaps \Delta E_1, \Delta E_2
and for the scaling quantity \Delta E_2 / \Delta E1 in different regimes of the
interaction parameter, and of the correlation length.Comment: LaTex, 27 pages, 9 figure
A High Precision Study of the QQ(bar) Potential from Wilson Loops in the Regime of String Breaking
For lattice QCD with two sea quark flavours we compute the static quark
antiquark potential V(R) in the regime where string breaking is expected. In
order to increase statistics, we make full use of the lattice information by
including all lattice vectors R to any possible lattice separation in the
infrared regime. The corresponding paths between the lattice points are
constructed by means of a generalized Bresenham algorithm as known from
computer graphics. As a results we achieve a determination of the unquenched
potential in the range .8 to 1.5 fm with hitherto unknown precision.
Furthermore, we demonstrate some error reducing methods for the evaluation of
the transition matrix element between two- and four-quark states.Comment: 6 pages, 7 figure
An Estimate of alpha_S from Bottomonium in Unquenched QCD
We estimate the strong coupling constant from the perturbative expansion of
the plaquette. The scale is set by the 2S-1S and 1P-1S splittings in
bottomonium which are computed in NRQCD on dynamical gauge configurations with
nf=2 degenerate Wilson quarks at intermediate masses. We have increased the
statistics of our spectrum calculation in order to reliably extrapolate in the
sea-quark mass. We find a value of alpha_MS(m_Z) = 0.1118(26) which is somewhat
lower than previous estimates within NRQCD.Comment: LATTICE98(heavyqk
Flavour singlet pseudoscalar masses in N_f = 2 QCD
We perform a lattice mass analysis in the flavour singlet pseudoscalar
channel on the SESAM and TXL full QCD vacuum configurations, with 2 active
flavours of dynamical Wilson fermions at beta = 5.6. At our inverse lattice
spacing, a^-1 = 2.3 GeV, we retrieve by a chiral extrapolation to the physical
light quark masses the value m_eta' = 3.7(+8)(-4) m_pi. A crude extrapolation
from (N_f = 3) phenomenology would suggest m_eta' \approx 5.1 m_pi for N_f = 2
QCD. we verify that the mass gap between the singlet state eta' and the pi
flavour triplt state is due to gauge configurations with non-trivial topology.Comment: 8 pages, 10 figure
Decorrelating Topology with HMC
The investigation of the decorrelation efficiency of the HMC algorithm with
respect to vacuum topology is a prerequisite for trustworthy full QCD
simulations, in particular for the computation of topology sensitive
quantities. We demonstrate that for mpi/mrho ratios <= 0.69 sufficient
tunneling between the topological sectors can be achieved, for two flavours of
dynamical Wilson fermions close to the scaling region beta=5.6. Our results are
based on time series of length 5000 trajectories.Comment: change of comments: LATTICE98(confine
The flavour singlet mesons in QCD
We study the flavour singlet mesons from first principles using lattice QCD.
We explore the splitting between flavour singlet and non-singlet for vector and
axial mesons as well as the more commonly studied cases of the scalar and
pseudoscalar mesons.Comment: 12 pages, LATEX, 4 ps figure
Light and Strange Hadron Spectroscopy with Dynamical Wilson Fermions
We present the final analysis of the light and strange hadron spectra from a full QCD lattice simulation with two degenerate dynamical sea quark flavours at corresponding to the range are investigated. For reference we also ran a quenched simulation at , which is the point of equal lattice spacing, . In the light sector, we find the chiral extrapolation to physical u- and d- masses to present a major source of uncertainty, comparable to the expected size of unquenching effects. From linear and quadratic fits we can estimate the errors on the hadron masses made from light quarks to be on a 15 % level prior to the continuum extrapolation. For the hadrons with strange valence quark content, the approximation to QCD appears not to cure the well-known failure of quenched QCD to reproduce the physical splitting
Flavor Singlet Meson Mass in the Continuum Limit in Two-Flavor Lattice QCD
We present results for the mass of the eta-prime meson in the continuum limit
for two-flavor lattice QCD, calculated on the CP-PACS computer, using a
renormalization-group improved gauge action, and Sheikholeslami and Wohlert's
fermion action with tadpole-improved csw. Correlation functions are measured at
three values of the coupling constant beta corresponding to the lattice spacing
a approx. 0.22, 0.16, 0.11 fm and for four values of the quark mass parameter
kappa corresponding to mpi over mrho approx. 0.8, 0.75, 0.7 and 0.6. For each
beta, kappa pair, 400-800 gauge configurations are used. The two-loop diagrams
are evaluated using a noisy source method. We calculate eta-prime propagators
using local sources, and find that excited state contributions are much reduced
by smearing. A full analysis for the smeared propagators gives
metaprime=0.960(87)+0.036-0.248 GeV, in the continuum limit, where the second
error represents the systematic uncertainty coming from varying the functional
form for chiral and continuum extrapolations.Comment: 9 pages, 19 figures, 4 table
On the low fermionic eigenmode dominance in QCD on the lattice
We demonstrate the utility of a spectral approximation to fermion loop
operators using low-lying eigenmodes of the hermitian Dirac-Wilson matrix, Q.
The investigation is based on a total of 400 full QCD vacuum configurations,
with two degenerate flavors of dynamical Wilson fermions at beta =5.6, at two
different sea quark masses. The spectral approach is highly competitive for
accessing both topological charge and disconnected diagrams, on large lattices
and small quark masses. We propose suitable partial summation techniques that
provide sufficient saturation for estimating Tr Q^{-1}, which is related to the
topological charge. In the effective mass plot of the eta' meson we achieved a
consistent early plateau formation, by ground state projecting the connected
piece of its propagator.Comment: 15 pages, 25 figures, citations adde
- …