110 research outputs found
On the spectral density of the Wilson operator
We summarize our recent determination [1] of the spectral density of the
Wilson operator in the p-regime of Wilson chiral perturbation theory. We
discuss the range of validity of our formula and a possible extension to our
computation in order to better understand the behaviour of the spectral density
in a finite volume close to the threshold.Comment: 7 pages, 2 figures, Proceedings for the XXIX International Symposium
on Lattice Field Theor
Corrections to the Banks-Casher relation with Wilson quarks
The Banks-Casher relation links the spectral density of the Dirac operator
with the existence of a chiral condensate and spontaneous breaking of chiral
symmetry. This relation receives corrections from a finite value of the quark
mass, a finite space-time volume and, if evaluated on a discrete lattice, from
the finite value of the lattice spacing a. We present a status report of a
determination of these corrections for Wilson quarks.Comment: 6 pages, 4 figures, Chiral Dynamics 2012 proceedin
Thermal operators and cluster topology in q-state Potts Model
We discuss a new class of identities between correlation functions which
arise from a local Z_2 invariance of the partition function of the q-state
Potts model on general graphs or lattices. Their common feature is to relate
the thermal operators of the Potts model to some topological properties of the
Fortuin-Kasteleyn clusters. In particular it turns out that any even
correlation function can be expressed in terms of observables which probe the
linking properties of these clusters. This generalises a class of analogous
relations recently found in the Ising model.Comment: 6 pages, latex, enlarged version, accepted for publication in Journal
of Physics
The epsilon regime with twisted mass Wilson fermions
We investigate the leading lattice spacing effects in mesonic two-point
correlators computed with twisted mass Wilson fermions in the epsilon-regime.
By generalizing the procedure already introduced for the untwisted Wilson
chiral effective theory, we extend the continuum chiral epsilon expansion to
twisted mass WChPT. We define different regimes, depending on the relative
power counting for the quark masses and the lattice spacing. We explicitly
compute, for arbitrary twist angle, the leading O(a^2) corrections appearing at
NLO in the so-called GSM^* regime. As in untwisted WChPT, we find that in this
situation the impact of explicit chiral symmetry breaking due to lattice
artefacts is strongly suppressed. Of particular interest is the case of maximal
twist, which corresponds to the setup usually adopted in lattice simulations
with twisted mass Wilson fermions. The formulae we obtain can be matched to
lattice data to extract physical low energy couplings, and to estimate
systematic uncertainties coming from discretization errors.Comment: 26 pages, 3 figure
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
Spectral density of the Hermitean Wilson Dirac operator: a NLO computation in chiral perturbation theory
We compute the lattice spacing corrections to the spectral density of the
Hermitean Wilson Dirac operator using Wilson Chiral Perturbation Theory at NLO.
We consider a regime where the quark mass and the lattice spacing obey
the relative power counting : in this situation
discretisation effects can be treated as perturbation of the continuum
behaviour. While this framework fails to describe lattice spectral density
close to the threshold, it allows nevertheless to investigate important
properties of the spectrum of the Wilson Dirac operator. We discuss the range
of validity of our results and the possible implications in understanding the
phase diagram of Wilson fermions.Comment: 27 pages, 4 figures; few typos corrected, added footnote, published
versio
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
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
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