90 research outputs found
Volume behaviour of quark condensate, pion mass and decay constant from Dyson-Schwinger equations
We solve the coupled system of Dyson-Schwinger and Bethe-Salpeter equations
for the quark propagator and the pion Bethe-Salpeter amplitude on a finite
volume. To this end we use a truncation scheme that includes pion cloud effects
in the quark propagator and light mesons. We study volume effects in the quark
condensate, the pion mass and the pion decay constant and compare to
corresponding results in other approaches. In general we find large effects for
volumes below V=(1.8 fm)^4.Comment: 10 pages, 9 figures, v2: minor clarifications, version accepted by
PR
Mixed action computations on fine dynamical lattices
We report on our first experiences in simulating Neuberger valence fermions
on CLS configurations with light sea quark masses and small lattice
spacings. Valence quark masses are considered that allow to explore the
matching to (partially quenched) chiral perturbation theory both in the
- and -regimes. The setup is discussed, and first results are
presented for spectral observables.Comment: 7 pages. Presented at the XXVII International Symposium on Lattice
Field Theory, July 26-31, 2009, Peking University, Beijing, Chin
Comparing the QCD potential in Perturbative QCD and Lattice QCD at large distances
We compare the perturbatively calculated QCD potential to that obtained from
lattice calculations in the theory without light quark flavours. We examine
E_tot(r) = 2 m_pole + V_QCD(r) by re-expressing it in the MSbar mass m =
m^MSbar(m^MSbar) and by choosing specific prescriptions for fixing the scale mu
(dependent on r and m). By adjusting m so as to maximise the range of
convergence, we show that perturbative and lattice calculations agree up to
3*r_0 ~ 7.5 GeV^-1 (r_0 is the Sommer scale) within the uncertainty of order
Lambda^3 r^2.Comment: Version to appear in Eur.J.Phys; 16 pages, 7 figure
Reweighting towards the chiral limit
We propose to perform fully dynamical simulations at small quark masses by
reweighting in the quark mass. This approach avoids some of the technical
difficulties associated with direct simulations at very small quark masses. We
calculate the weight factors stochastically, using determinant breakup and low
mode projection to reduce the statistical fluctuations. We find that the weight
factors fluctuate only moderately on nHYP smeared dynamical Wilson-clover
ensembles, and we could successfully reweight 16^4, (1.85fm)^4 volume
configurations from m_q = 20MeV to m_q = 5MeV quark masses, reaching the
epsilon-regime. We illustrate the strength of the method by calculating the low
energy constant F from the epsilon-regime pseudo-scalar correlator.Comment: 17 pages, 8 figure
Testing a Topology Conserving Gauge Action in QCD
We study lattice QCD with a gauge action, which suppresses small plaquette
values. Thus the MC history is confined to a single topological sector over a
significant time, while other observables are decorrelated. This enables the
cumulation of statistics with a specific topological charge, which is needed
for simulations of QCD in the -regime. The same action may also be
useful for simulations with dynamical quarks. The update is performed with a
local HMC algorithm.Comment: 3 pages, 3 figures, poster presented by S. Shcheredin at
Lattice2004(theory
Exploring Topology Conserving Gauge Actions for Lattice QCD
We explore gauge actions for lattice QCD, which are constructed such that the
occurrence of small plaquette values is strongly suppressed. By choosing strong
bare gauge couplings we arrive at values for the physical lattice spacings of
O(0.1 fm). Such gauge actions tend to confine the Monte Carlo history to a
single topological sector. This topological stability facilitates the
collection of a large set of configurations in a specific sector, which is
profitable for numerical studies in the epsilon-regime. The suppression of
small plaquette values is also expected to be favourable for simulations with
dynamical quarks. We use a local Hybrid Monte Carlo algorithm to simulate such
actions, and we present numerical results for the static potential, the
physical scale, the topological stability and the kernel condition number of
the overlap Dirac operator. In addition we discuss the question of reflection
positivity for a class of such gauge actions.Comment: 28 pages, 8 figure
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