13 research outputs found
Lattice Gauge Actions for Fixed Topology
We test a set of lattice gauge actions for QCD that suppress small plaquette
values and in this way also suppress transitions between topological sectors.
This is well suited for simulations in the epsilon-regime and it is expected to
help in numerical simulations with dynamical quarks.Comment: 3 pages. Talk presented at Quark Confinement and the Hadron Spectrum
VI, Villasimius, Sardinia, Italy, September 21-25, 2004. References adde
Reducing cutoff effects in maximally twisted lattice QCD close to the chiral limit
When analyzed in terms of the Symanzik expansion, lattice correlators of
multi-local (gauge-invariant) operators with non-trivial continuum limit
exhibit in maximally twisted lattice QCD ``infrared divergent'' cutoff effects
of the type a^{2k}/(m_\pi^2)^{h}, 2k\geq h\geq 1 (k,h integers), which tend to
become numerically large when the pion mass gets small. We prove that, if the
action is O(a) improved a` la Symanzik or, alternatively, the critical mass
counter-term is chosen in some ``optimal'' way, these lattice artifacts are
reduced to terms that are at worst of the order a^{2}(a^2/m_\pi^2)^{k-1}, k\geq
1. This implies that the continuum extrapolation of lattice results is smooth
at least down to values of the quark mass, m_q, satisfying the order of
magnitude inequality m_q >a^2\Lambda^3_{\rm QCD}.Comment: 23 pages, no figures. Revised version, published by JHEP. Various
sections shortened, alternative determination of the "optimal" critical mass
discussed, section about the pion decay constant inserted. Conclusions
unchange
On the renormalized scalar density in quenched QCD
We present a non-perturbative determination of the renormalization factor Z_S
of the scalar density in quenched QCD with overlap fermions. Results are
obtained at four values of the lattice spacing. By combining Z_S with results
for the low-energy constant Sigma we are able to compute the renormalization
group invariant scalar condensate in the continuum limit with a total accuracy
of 7%, excluding dynamical quark effects. Our result translates to
Sigma_msbar(2 GeV)=(285+/-9 MeV)^3 if the scale is set by the kaon decay
constant. We have also performed scaling studies of the pseudoscalar decay
constant and the vector mass. Our results indicate that quantities computed
using overlap quarks exhibit excellent scaling behaviour, with small residual
lattice artifacts.Comment: 15 pages, 7 figure
Flavour Breaking Effects of Wilson twisted mass fermions
We study the flavour breaking effects appearing in the Wilson twisted mass
formulation of lattice QCD. In this quenched study, we focus on the mass
splitting between the neutral and the charged pion, determining the neutral
pion mass with a stochastic noise method to evaluate the disconnected
contributions. We find that these disconnected contributions are significant.
Using the Osterwalder-Seiler interpretation of the connected piece of the
neutral pion correlator, we compute the corresponding neutral pion mass to
study with more precision the scaling behaviour of the mass splitting.Comment: 15 pages, 2 figure
Light hadron and diquark spectroscopy in quenched QCD with overlap quarks on a large lattice
A simulation of quenched QCD with the overlap Dirac operator has been
completed using 100 Wilson gauge configurations at beta = 6 on an 18^3 x 64
lattice and at beta = 5.85 on a 14^3 x 48 lattice, both in Landau gauge. We
present results for light meson and baryon masses, meson final state "wave
functions," and other observables, as well as some details on the numerical
techniques that were used. Our results indicate that scaling violations, if
any, are small. We also present an analysis of diquark correlations using the
quark propagators generated in our simulation.Comment: 28 LaTeX pages, 41 figures, v2: minor updates, version published in
JHE
Going chiral: overlap versus twisted mass fermions
We compare the behavior of overlap fermions, which are chirally invariant,
and of Wilson twisted mass fermions at full twist in the approach to the chiral
limit. Our quenched simulations reveal that with both formulations of lattice
fermions pion masses of O(250 MeV) can be reached in practical applications.
Our comparison is done at a fixed value of the lattice spacing a=0.123 fm. A
number of quantities are measured such as hadron masses, pseudoscalar decay
constants and quark masses obtained from Ward identities. We also determine the
axial vector renormalization constants in the case of overlap fermions.Comment: 22 pages, 10 figure
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
Quenched Scaling of Wilson twisted mass fermions
We investigate the scaling behaviour of quenched Wilson twisted mass fermions at maximal twist applying two definitions of the critical mass. The first definition uses the vanishing of the pseudoscalar meson mass m_PS while the second employs the vanishing of the PCAC quark mass m_PCAC. We confirm in both cases the expected O(a) improvement. In addition, we show that the PCAC quark mass definition leads to substantially reduced O(a^2) cut-off effects even when the pseudoscalar meson mass m_PS is as small as 270 MeV. At a fixed value of m_PS we perform continuum limits for the vector meson mass m_V and for the pseudoscalar decay constant f_PS and discuss the renormalisation constant Z_V of the vector current