1,536 research outputs found
Chiral symmetry breaking and topology for all N
We investigate spontaneous chiral symmetry breaking in SU(N) gauge theories
at large N using overlap fermions. The exact zero modes and the low-lying modes
of the Dirac operator provide the tools to gain insight into the interplay
between chiral symmetry breaking and topology. We find that topology indeed
drives chiral symmetry breaking at N=3 as well as at large N. By comparing the
results on various volumes and at different lattice spacings we are able to
show that our conclusions are not affected by finite volume effects and also
hold in the continuum limit. We then address the question whether the topology
can be usefully described in terms of instantons.Comment: Talk at Lattice 2003 (chiral); 3 pages, 2 figures, espcrc2.st
The static quark potential from the gauge invariant Abelian decomposition
We investigate the relationship between colour confinement and topological
structures derived from the gauge invariant Abelian (Cho-Duan-Ge)
decomposition. This Abelian decomposition is made imposing an isometry on a
colour field which selects the Abelian direction; the principle novelty of
our study is that we have defined this field in terms of the eigenvectors of
the Wilson Loop. This allows us to establish an equivalence between the path
ordered integral of the non-Abelian gauge fields with an integral over an
Abelian restricted gauge field which is tractable both theoretically and
numerically in lattice QCD. By using Stokes' theorem, we can relate the Wilson
Loop in terms of a surface integral over a restricted field strength, and show
that the restricted field strength may be dominated by topological structures,
which occur when one of the parameters parametrising the colour field winds
itself around a non-analyticity in the colour field. If they exist, these
objects will lead to an area law scaling for the Wilson Loop and provide a
mechanism for quark confinement. We search for these structures in quenched
lattice QCD. We perform the Abelian decomposition, and find that the restricted
field strength is dominated by peaks on the lattice. Wilson Loops containing
these peaks show a stronger area-Law and thus provide the dominant contribution
to the string tension.Comment: 8 pages, 3 figures; v2 some minor changes (including updated
numerical results), accepted for publication in Physics Letter
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Sediment structure and physicochemical changes following tidal inundation at a large open coast managed realignment site
Managed realignment (MR) schemes are being implemented to compensate for the loss of intertidal saltmarsh habitats by breaching flood defences and inundating the formerly defended coastal hinterland. However, studies have shown that MR sites have lower biodiversity than anticipated, which has been linked with anoxia and poor drainage resulting from compaction and the collapse of sediment pore space caused by the site's former terrestrial land use. Despite this proposed link between biodiversity and soil structure, the evolution of the sediment sub-surface following site inundation has rarely been examined, particularly over the early stages of the terrestrial to marine or estuarine transition. This paper presents a novel combination of broad- and intensive-scale analysis of the sub-surface evolution of the Medmerry Managed Realignment Site (West Sussex, UK) in the three years following site inundation. Repeated broad-scale sediment physiochemical datasets are analysed to assess the early changes in the sediment subsurface and the preservation of the former terrestrial surface, comparing four locations of different former land uses. Additionally, for two of these locations, high-intensity 3D-computed X-ray microtomography and Itrax micro-X-ray fluorescence spectrometry analyses are presented. Results provide new data on differences in sediment properties and structure related to the former land use, indicating that increased agricultural activity leads to increased compaction and reduced porosity. The presence of anoxic conditions, indicative of poor hydrological connectivity between the terrestrial and post-inundation intertidal sediment facies, was only detected at one site. This site has experienced the highest rate of accretion over the terrestrial surface (ca. 7 cm over 36 months), suggesting that poor drainage is caused by the interaction (or lack of) between sediment facies rather than the former land use. This has significant implications for the design of future MR sites in terms of preparing sites, their anticipated evolution, and the delivery of ecosystem services
The operator product expansion on the lattice
We investigate the Operator Product Expansion (OPE) on the lattice by
directly measuring the product (where J is the vector current) and
comparing it with the expectation values of bilinear operators. This will
determine the Wilson coefficients in the OPE from lattice data, and so give an
alternative to the conventional methods of renormalising lattice structure
function calculations. It could also give us access to higher twist quantities
such as the longitudinal structure function F_L = F_2 - 2 x F_1. We use overlap
fermions because of their improved chiral properties, which reduces the number
of possible operator mixing coefficients.Comment: 7 pages, 4 postscript figures. Contribution to Lattice 2007,
Regensbur
Hadron Spectroscopy with Dynamical Chirally Improved Fermions
We simulate two dynamical, mass degenerate light quarks on 16^3x32 lattices
with a spatial extent of 2.4 fm using the Chirally Improved Dirac operator. The
simulation method, the implementation of the action and signals of
equilibration are discussed in detail. Based on the eigenvalues of the Dirac
operator we discuss some qualitative features of our approach. Results for
ground state masses of pseudoscalar and vector mesons as well as for the
nucleon and delta baryons are presented.Comment: 26 pages, 17 figures, 10 table
Quark structure from the lattice Operator Product Expansion
We have reported elsewhere in this conference on our continuing project to
determine non-perturbative Wilson coefficients on the lattice, as a step
towards a completely non-perturbative determination of the nucleon structure.
In this talk we discuss how these Wilson coefficients can be used to extract
Nachtmann moments of structure functions, using the case of off-shell
Landau-gauge quarks as a first simple example. This work is done using overlap
fermions, because their improved chiral properties reduce the difficulties due
to operator mixing.Comment: 7 pages, 3 figures. Talk given at the XXVII International Symposium
on Lattice Field Theory, July 26-31 2009, Peking University, Beijing, Chin
Gap Domain Wall Fermions
I demonstrate that the chiral properties of Domain Wall Fermions (DWF) in the
large to intermediate lattice spacing regime of QCD, 1 to 2 GeV, are
significantly improved by adding to the action two standard Wilson fermions
with supercritical mass equal to the negative DWF five dimensional mass. Using
quenched DWF simulations I show that the eigenvalue spectrum of the transfer
matrix Hamiltonian develops a substantial gap and that the residual mass
decreases appreciatively. Furthermore, I confirm that topology changing remains
active and that the hadron spectrum of the added Wilson fermions is above the
lattice cutoff and therefore is irrelevant. I argue that this result should
also hold for dynamical DWF and furthermore that it should improve the chiral
properties of related fermion methods.Comment: 12 pages of text, 14 figures, added sect.6 on topology and reference
Patient Safety and Quality Improvement Education for Paramedics: Peacticing What We Preach
Our patients expect and deserve safe, high-quality care. Paramedics have a personal responsibility for providing safe care, regardless of previous education or regulatory framework. The onus is on us all to ensure that paramedics are adequately prepared to address this responsibility
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