3,573 research outputs found
Short distance singularities and automatic O() improvement: the cases of the chiral condensate and the topological susceptibility
Short-distance singularities in lattice correlators can modify their Symanzik
expansion by leading to additional O() lattice artifacts. At the example of
the chiral condensate and the topological susceptibility, we show how to
account for these lattice artifacts for Wilson twisted mass fermions and show
that the property of automatic O() improvement is preserved at maximal
twist.Comment: 12 pages, corrected proof for topological susceptibility, version
published in JHE
Topological susceptibility from twisted mass fermions using spectral projectors
We discuss the computation of the topological susceptibility using the method
of spectral projectors and dynamical twisted mass fermions. We present our
analysis concerning the O(a)-improvement of the topological susceptibility and
we show numerical results for Nf=2 and Nf=2+1+1 flavours, performing a study of
the quark mass dependence in terms of leading order chiral perturbation theory.Comment: 7 pages, 3 figures; presented at the 31st International Symposium on
Lattice Field Theory (Lattice 2013), 29 July - 3 August 2013, Mainz, German
Computation of the chiral condensate using and dynamical flavors of twisted mass fermions
We apply the spectral projector method, recently introduced by Giusti and
L\"uscher, to compute the chiral condensate using and
dynamical flavors of maximally twisted mass fermions. We present our results
for several quark masses at three different lattice spacings which allows us to
perform the chiral and continuum extrapolations. In addition we report our
analysis on the improvement of the chiral condensate for twisted mass
fermions. We also study the effect of the dynamical strange and charm quarks by
comparing our results for and dynamical flavors.Comment: 7 pages, 3 figures; presented at the 31st International Symposium on
Lattice Field Theory (Lattice 2013), 29 July - 3 August 2013, Mainz, German
Testing the Witten-Veneziano Formula on the Lattice
In this proceeding contribution we report on a test of the famous
Witten-Veneziano formula using lattice techniques. We perform dedicated
quenched simulations and apply the spectral projector method to determine the
topological susceptibility in pure Yang-Mills theory. In order to compute the
relevant meson masses and the flavor singlet decay constant we employ lattice
QCD with dynamical Wilson twisted mass fermions. Taking the
continuum and the chiral limits we find good agreement within
uncertainties for both sides of the formula.Comment: 7 pages, 4 figures, presented at the 33rd International Symposium on
Lattice Field Theory, 14 -18 July 2015, Kobe International Conference Center,
Kobe, Japa
Comparison of different lattice definitions of the topological charge
We present a comparison of different definitions of the topological charge on
the lattice, using a small-volume ensemble with 2 flavours of dynamical twisted
mass fermions. The investigated definitions are: index of the overlap Dirac
operator, spectral projectors, spectral flow of the Hermitian Wilson-Dirac
operator and field theoretic with different kinds of smoothing of gauge fields
(HYP and APE smearings, gradient flow, cooling). We also show some results on
the topological susceptibility.Comment: 7 pages, 2 figures, presented at the 32nd International Symposium on
Lattice Field Theory (Lattice 2014), 23-28 June 2014, Columbia University,
New York, NY, US
First results with twisted mass fermions towards the computation of parton distribution functions on the lattice
We report on our exploratory study for the evaluation of the parton
distribution functions from lattice QCD, based on a new method proposed in
Ref.~arXiv:1305.1539. Using the example of the nucleon, we compare two
different methods to compute the matrix elements needed, and investigate the
application of gauge link smearing. We also present first results from a large
production ensemble and discuss the future challenges related to this method.Comment: 7 pages, 4 figures, talk given at the 32nd International Symposium on
Lattice Field Theory (Lattice 2014), June 23-28 2014, New York, US
Current Treatment for Carpal Tunnel Syndrome
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The influence of breeding colony and sex on levels of mercury, selenium and lead levels and carbon and nitrogen stable isotope signatures in summer and winter feathers of Calonectris shearwaters
Contamination in marine foodwebs is nowadays of great environmental concern owing to the increasing levels of pollution in marine ecosystems from different anthropogenic sources. Seabirds can be used as indicators of regional contaminant patterns across large temporal and spatial scales. We analysed Hg, Se and Pb levels as well as stable isotope ratios of C (13C/12C, δ13C) and N (15N/14N, δ15N) in breeding- and winter-season feathers on males and females of two related shearwater species, providing information on spatiotemporal patterns of contaminants as well as the influence of the trophic ecology of these seabirds on contaminant levels. During the breeding season, Se and Pb concentrations were highest at the Cape Verde archipelago, showing no differences among the other colonies or between the sexes. However, Hg levels varied among colonies, being highest in the Mediterranean, probably resulting from the larger emissions and fallout of this pollutant in Europe. Feathers grown during breeding also showed sexual differences in Hg concentrations and δ13C. Differences in Hg concentration between sexes are mainly due to egg-laying decontamination in females. In contrast, differences in Hg among colonies are probably related to differences in trophic ecology, as indicated by δ13C and δ15N measurements. Contaminant concentrations in winter-grown feathers did not show any relationship with stable isotope values but were affected by contaminant loads associated with the breeding season. These findings suggest that the interpretation of contaminant levels of migratory species from feathers moulted out of the breeding season should be made with caution because those values could reflect exposures to contaminants acquired during the breeding season. We conclude that factors other than feeding ecology may play an important role in the interpretation of contaminant levels and their annual dynamics at several spatial scales. Consideration of the relevant temporal context provided by isotopic signatures and contaminant concentrations is important in deciphering contaminant information based on various tissues
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