7,960 research outputs found
Low-dimensional long-range topological structure in the QCD vacuum
Lattice topological charge associated with Ginsparg-Wilson fermions exhibits
generic topological stability over quantum ensemble of configurations
contributing to the QCD path integral. Moreover, the underlying chiral symmetry
leads to the suppression of ultraviolet noise in the associated topological
charge densities ("chiral smoothing"). This provides a solid foundation for the
direct study of the role of topological charge fluctuations in the physics of
QCD vacuum. Using these tools it was recently demonstrated that: (a) there is a
well-defined space-time structure (order) in topological charge density
(defined through overlap fermions) for typical configurations contributing to
QCD path integral; (b) this fundamental structure is low-dimensional,
exhibiting sign-coherent behavior on subsets of dimension less than four and
not less than one; (c) the structure has a long-range global character
(spreading over maximal space-time distances) and is built around the locally
one-dimensional network of strong fields (skeleton). In this talk we elaborate
on certain aspects and implications of these results.Comment: 3 pages, 1 figure; Lattice2003(topology
Advanced Very High Resolution Radiometer (AVHRR) data evaluation for use in monitoring vegetation. Volume 1: Channels 1 and 2
Data from the National Oceanic and Atmospheric Administration satellite system (NOAA-6 satellite) were analyzed to study their nonmeteorological uses. A file of charts, graphs, and tables was created form the products generated. It was found that the most useful data lie between pixel numbers 400 and 2000 on a given scan line. The analysis of the generated products indicates that the Gray-McCrary Index can discern vegetation and associated daily and seasonal changes. The solar zenith-angle correction used in previous studies was found to be a useful adjustment to the index. The METSAT system seems best suited for providing large-area analyses of surface features on a daily basis
Pion Decay Constant, and Chiral Log from Overlap Fermions
We report our calculation of the pion decay constant , the axial
renormalization constant , and the quenched chiral logarithms from the
overlap fermions. The calculation is done on a quenched lattice at
fm using tree level tadpole improved gauge action. The smallest pion
mass we reach is about 280 MeV. The lattice size is about 4 times the Compton
wavelength of the lowest mass pion.Comment: Lattice2001(Hadronic Matrix Elements), 3pages, 5figure
Coherent Topological Charge Structure in Models and QCD
In an effort to clarify the significance of the recent observation of
long-range topological charge coherence in QCD gauge configurations, we study
the local topological charge distributions in two-dimensional sigma
models, using the overlap Dirac operator to construct the lattice topological
charge. We find long-range sign coherence of topological charge along extended
one-dimensional structures in two-dimensional spacetime. We discuss the
connection between the long range topological structure found in and
the observed sign coherence along three-dimensional sheets in four-dimensional
QCD gauge configurations. In both cases, coherent regions of topological charge
form along membrane-like surfaces of codimension one. We show that the Monte
Carlo results, for both two-dimensional and four-dimensional gauge theory,
support a view of topological charge fluctuations suggested by Luscher and
Witten. In this framework, the observed membranes are associated with
boundaries between ``k-vacua,'' characterized by an effective local value of
which jumps by across the boundary.Comment: 26 page
Influence of an Internal Magnetar on Supernova Remnant Expansion
Most of the proposed associations between magnetars and supernova remnant
suffer from age problems. Usually, supernova remnants ages are determined from
an approximation of the Sedov-Taylor phase relation between radius and age, for
a fixed energy of the explosion ~ 10^{51} erg. Those ages do not generally
agree with the characteristic ages of the (proposed) associated magnetars. We
show quantitatively that, by taking into account the energy injected on the
supernova remnant by magnetar spin-down, a faster expansion results, improving
matches between characteristic ages and supernova remnants ages. However, the
magnetar velocities inferred from observations would inviabilize some
associations. Since characteristic ages may not be good age estimators, their
influence on the likelihood of the association may not be as important.
In this work we present simple numerical simulations of supernova remnants
expansion with internal magnetars, and apply it to the observed objects. A
short initial spin period, thought to be important for the very generation of
the magnetic field, is also relevant for the modified expansion of the remnant.
We next analyze all proposed associations case-by-case, addressing the
likelyhood of each one, according to this perspective. We consider a larger
explosion energy and reasses the characteristic age issue, and conclude that
about 50% of the associations can be true ones, provided SGRs and AXPs are
magnetars.Comment: 30 pages, AAStex, 5 figures, format fixe
Chiral Properties of Pseudoscalar Mesons on a Quenched Lattice with Overlap Fermions
The chiral properties of the pseudoscalar mesons are studied numerically on a
quenched lattice with the overlap fermion. We elucidate the role of the
zero modes in the meson propagators, particularly that of the pseudoscalar
meson. The non-perturbative renormalization constant is determined from
the axial Ward identity and is found to be almost independent of the quark mass
for the range of quark masses we study; this implies that the error is
small. The pion decay constant, , is calculated from which we
determine the lattice spacing to be 0.148 fm. We look for quenched chiral log
in the pseudoscalar decay constants and the pseudoscalar masses and we find
clear evidence for its presence. The chiral log parameter is
determined to be in the range 0.15 -- 0.4 which is consistent with that
predicted from quenched chiral perturbation theory.Comment: Version accepted for publication by PRD. A few minor typographical
errors have been corrected. 24 pages, 11 figure
Independent sexual violence advisers (ISVAs) in England, Wales and Northern Ireland: a study of impacts, effects, coping mechanisms and effective support systems for people working as ISVAs and ISVA Managers
This study is the first of its kind in England, Wales and Northern Ireland and was carried out to gather information about the impact of working as Independent Sexual Violence Advisers (ISVAs) or ISVA Managers. The ISVA role is relatively new, and as such, little is known about this difficult and emotionally charged work. Although some literature looks at the impact of working in the sexual violence field, there is little from England, Wales or Northern Ireland, and even less focused on the direct, ongoing, face-to-face work ISVAs do. This report focuses on the impacts, effects, coping mechanisms and effective support systems for people working as ISVAs and ISVA Managers in supporting victim-survivors of sexual violence across England, Wales and Northern Ireland. Since its introduction in 2005, the ISVA role has been invaluable in providing continuous support to victim-survivors of sexual violence and working to meet their emotional and practical needs during the criminal justice process. As conviction rates are at an all-time low, ISVAs can also provide support to people who may otherwise feel let down by the Criminal Justice System. ISVAs can also support people who do not want to report the crime to the police – helping people at, potentially, the lowest point of their life. This survey focused on providing an overview of the ISVA role (e.g. context they work in, caseloads, supervision and support available) and determining which factors predict the likelihood of experiencing negative and positive impacts as a result of the work they do
Uncovering Low-Dimensional Topological Structure in the QCD Vacuum
Recently, we have pointed out that sign-coherent 4-dimensional structures can
not dominate topological charge fluctuations in QCD vacuum at all scales. Here
we show that an enhanced lower-dimensional coherence is possible. In pure SU(3)
lattice gauge theory we find that in a typical equilibrium configuration about
80% of space-time points are covered by two oppositely-charged connected
structures built of elementary 3-dimensional coherent hypercubes. The
hypercubes within the structure are connected through 2-dimensional common
faces. We suggest that this coherence is a manifestation of a low-dimensional
order present in the QCD vacuum. The use of a topological charge density
associated with Ginsparg-Wilson fermions ("chiral smoothing") is crucial for
observing this structure.Comment: 3 pages, 1 figure; Proceedings of the "Confinement V" Conference,
Gargnano, Italy, Sep 10-14, 200
Topological Charge Correlators, Spectral Bounds, and Contact Terms
The structure of topological charge fluctuations in the QCD vacuum is
strongly restricted by the spectral negativity of the Euclidean 2-point
correlator for and the presence of a positive contact term. Some
examples are considered which illustrate the physical origin of these
properties.Comment: Lattice 2002 Conference Proceeding
Locality and topology with fat link overlap actions
We study the locality and topological properties of fat link clover overlap
(FCO) actions. We find that a small amount of fattening (2-4 steps of APE or 1
step of HYP) already results in greatly improved properties compared to the
Wilson overlap (WO). We present a detailed study of the localisation of the FCO
and its connection to the density of low modes of . In contrast to
the Wilson overlap, on quenched gauge backgrounds we do not find any dependence
of the localization of the FCO on the gauge coupling. This suggests that the
FCO remains local in the continuum limit. The FCO also faithfully reproduces
the zero mode wave functions of typical lattice instantons, not like the Wilson
overlap. After a general discussion of different lattice definitions of the
topological charge we also show that the FCO together with the Boulder charge
are likely to satisfy the index theorem in the continuum limit. Finally, we
present a high statistics computation of the quenched topological
susceptibility with the FCO action.Comment: 19 pages, LaTe
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