1,187 research outputs found
Topology of SU(N) gauge theories at T=0 and T=Tc
We calculate the topological charge density of SU(N) lattice gauge fields for
values of N up to N=8. Our T=0 topological susceptibility appears to approach a
finite non-zero limit at N=infinity that is consistent with earlier
extrapolations from smaller values of N. Near the deconfining temperature Tc we
are able to investigate separately the confined and deconfined phases, since
the transition is quite strongly first order. We find that the topological
susceptibility of the confined phase is always very similar to that at T=0. By
contrast, in the deconfined phase at larger N there are no topological
fluctuations except for rare, isolated and small instantons. This shows that as
N->infinity the large-T suppression of large instantons and the large-N
suppression of small instantons overlap, even at T=Tc, so as to suppress all
topological fluctuations in the deconfined phase. In the confined phase by
contrast, the size distribution is much the same at all T, becoming more peaked
as N grows, suggesting that D(rho) is proportional to a delta function at
N=infinity, centered on rho close to 1/Tc.Comment: 31 page
Quantifying innovation in surgery
Objectives: The objectives of this study were to assess the applicability of patents and publications as metrics of surgical technology and innovation; evaluate the historical relationship between patents and publications; develop a methodology that can be used to determine the rate of innovation growth in any given health care technology. Background: The study of health care innovation represents an emerging academic field, yet it is limited by a lack of valid scientific methods for quantitative analysis. This article explores and cross-validates 2 innovation metrics using surgical technology as an exemplar. Methods: Electronic patenting databases and the MEDLINE database were searched between 1980 and 2010 for âsurgeonâ OR âsurgicalâ OR âsurgery.â Resulting patent codes were grouped into technology clusters. Growth curves were plotted for these technology clusters to establish the rate and characteristics of growth. Results: The initial search retrieved 52,046 patents and 1,801,075 publications. The top performing technology cluster of the last 30 years was minimally invasive surgery. Robotic surgery, surgical staplers, and image guidance were the most emergent technology clusters. When examining the growth curves for these clusters they were found to follow an S-shaped pattern of growth, with the emergent technologies lying on the exponential phases of their respective growth curves. In addition, publication and patent counts were closely correlated in areas of technology expansion. Conclusions: This article demonstrates the utility of publically available patent and publication data to quantify innovations within surgical technology and proposes a novel methodology for assessing and forecasting areas of technological innovation
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
The deconfinement transition in SU(N) gauge theories
We investigate the properties of the deconfinement transition in SU(4) and
SU(6) gauge theories. We find that it is a `normal' first order transition in
both cases, from which we conclude that the transition is first order in the
N->infinity limit. Comparing our preliminary estimates of the continuum values
of Tc/sqrt(K) with existing values for SU(2) and SU(3) demonstrates a weak
dependence on N for all values of N.Comment: 18 page
Non-perturbative improvement of stout-smeared three flavour clover fermions
We discuss a 3-flavour lattice QCD action with clover improvement in which
the fermion matrix has single level stout smearing for the hopping terms
together with unsmeared links for the clover term. With the (tree-level)
Symanzik improved gluon action this constitutes the Stout Link Non-perturbative
Clover or SLiNC action. To cancel O(a) terms the clover term coefficient has to
be tuned. We present here results of a non-perturbative determination of this
coefficient using the Schroedinger functional and as a by-product a
determination of the critical hopping parameter. Comparisons of the results are
made with lowest order perturbation theory.Comment: 30 pages, 13 figures, minor changes, published versio
Low-Dimensional Long-Range Topological Charge Structure in the QCD Vacuum
While sign-coherent 4-dimensional structures cannot dominate topological
charge fluctuations in the QCD vacuum at all scales due to reflection
positivity, it is possible that enhanced coherence exists over extended
space-time regions of lower dimension. Using the overlap Dirac operator to
calculate topological charge density, we present evidence for such structure in
pure-glue SU(3) lattice gauge theory. It is found that a typical equilibrium
configuration is dominated by two oppositely-charged sign-coherent connected
structures (``sheets'') covering about 80% of space-time. Each sheet is built
from elementary 3-d cubes connected through 2-d faces, and approximates a
low-dimensional curved manifold (or possibly a fractal structure) embedded in
the 4-d space. At the heart of the sheet is a ``skeleton'' formed by about 18%
of the most intense space-time points organized into a global long-range
structure, involving connected parts spreading over maximal possible distances.
We find that the skeleton is locally 1-dimensional and propose that its
geometrical properties might be relevant for understanding the possible role of
topological charge fluctuations in the physics of chiral symmetry breaking.Comment: 4 pages RevTeX, 4 figures; v2: 6 pages, 5 figures, more explanations
provided, figure and references added, published versio
Filtered overlap: speedup, locality, kernel non-normality and Z_A~1
We investigate the overlap operator with a UV filtered Wilson kernel. The
filtering leads to a better localization of the operator even on coarse
lattices and with the untuned choice . Furthermore, the axial-vector
renormalization constant is much closer to 1, reducing the mismatch with
perturbation theory. We show that all these features persist over a wide range
of couplings and that the details of filtering prove immaterial. We investigate
the properties of the kernel spectrum and find that the kernel non-normality is
reduced. As a side effect we observe that for certain applications of the
filtered overlap a speed-up factor of 2-4 can be achieved.Comment: 30 pp, 23 fig
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