44,757 research outputs found
Domain Wall Fermions with Exact Chiral Symmetry
We show how the standard domain wall action can be simply modified to allow
arbitrarily exact chiral symmetry at finite fifth dimensional extent. We note
that the method can be used for both quenched and dynamical calculations. We
test the method using smooth and thermalized gauge field configurations. We
also make comparisons of the performance (cost) of the domain wall operator for
spectroscopy compared to other methods such as the overlap-Dirac operator and
find both methods are comparable in cost.Comment: revtex, 37 pages, 11 color postscript figure
The preparation and properties of luminiscent films on silicon
The interconnection problems in solid state electroluminescent displays, due to complex addressing and memory requirements, can be minimised by making a monolithic device in which light is produced in a thin film on silicon and controlled by underlying integrated circuitry. This thesis describes the preparation and properties of some luminescent films for this application. Preliminary work was aimed at depositing epitaxial ZnS phosphor films on silicon but, due to problems of reproducibility and activation, this was not a success. Its termination, however, was prompted mainly by another reason; the discovery by the author of the phosphor willemite (Zn(_2)Si0(_4):Mn) which seemed admirably suited for deposition as a thin luminescent film on silicon integrated circuitry. The main advantage was the novel method of fabrication1which involved the conversion of an oxide layer on the silicon surface to willemite by reaction with an evaporated film of ZnF(_2):Mn. The films produced were composed of microcryetallites embedded in a matrix of unreacted oxide. They were brightly green oathodoluminescent. In an MIS structure the current was assymetrical with bias. For negative and low positive bias on the metal the films were highly insulating but with high positive bias relatively large currents flowed accompanied by weak green electroluminescence. A conduction model, based on capacitance-voltage, current-voltage and luminescence experiments, has been proposed. In this, mobile positive ions in the. film discharge only when the cathode is metal so that with positive bias, they accumulate in front of the silicon where field intensification occurs. Electrons then tunnel from the silicon to collision excite the luminescence of manganese centres in the willemite. The observation of d.c. electroluminescence i4 thin films of willemite together with the ease and reproducibility of the fabrication process and its apparent compatibility with silicon technology, is thought to be a significant step in the development of a monolithic display based on silicon
First Calculation of Hyperon Axial Couplings from Lattice QCD
In this work, we report the first lattice calculation of hyperon axial
couplings, using the 2+1-flavor MILC configurations and domain-wall fermion
valence quarks. Both the and axial couplings are computed for
the first time in lattice QCD. In particular we find that and .Comment: 5 pages, 2 figure
Mixed Meson Masses with Domain-Wall Valence and Staggered Sea Fermions
Mixed action lattice calculations allow for an additive lattice spacing
dependent mass renormalization of mesons composed of one sea and one valence
quark, regardless of the type of fermion discretization methods used in the
valence and sea sectors. The value of the mass renormalization depends upon the
lattice actions used. This mixed meson mass shift is an important lattice
artifact to determine for mixed action calculations; because it modifies the
pion mass, it plays a central role in the low energy dynamics of all hadronic
correlation functions. We determine the leading order, , and
next to leading order, , additive mass shift of
\textit{valence-sea} mesons for a mixed lattice action with domain-wall valence
fermions and rooted staggered sea fermions, relevant to the majority of current
large scale mixed action lattice efforts. We find that on the asqtad improved
coarse MILC lattices, this additive mass shift is well parameterized in lattice
units by , which in physical
units, using fm, corresponds to . In terms of the mixed action effective field
theory parameters, the corresponding mass shift is given by at leading order plus
next-to-leading order corrections including the necessary chiral logarithms for
this mixed action calculation, determined in this work. Within the precision of
our calculation, one can not distinguish between the full next-to-leading order
effective field theory analysis of this additive mixed meson mass shift and the
parameterization given above.Comment: 28 pages, 3 figures, 5 table
Radiative Transitions in Charmonium from Lattice QCD
Radiative transitions between charmonium states offer an insight into the
internal structure of heavy-quark bound states within QCD. We compute, for the
first time within lattice QCD, the transition form-factors of various
multipolarities between the lightest few charmonium states. In addition, we
compute the experimentally unobservable, but physically interesting vector
form-factors of the and .
To this end we apply an ambitious combination of lattice techniques,
computing three-point functions with heavy domain wall fermions on an
anisotropic lattice within the quenched approximation. With an anisotropy
at we find a reasonable gross spectrum and a
hyperfine splitting , which compares favourably with
other improved actions.
In general, after extrapolation of lattice data at non-zero to the
photopoint, our results agree within errors with all well measured experimental
values. Furthermore, results are compared with the expectations of simple quark
models where we find that many features are in agreement; beyond this we
propose the possibility of constraining such models using our extracted values
of physically unobservable quantities such as the quadrupole moment.
We conclude that our methods are successful and propose to apply them to the
problem of radiative transitions involving hybrid mesons, with the eventual
goal of predicting hybrid meson photoproduction rates at the GlueX experiment.Comment: modified version as publishe
Approach to the Continuum Limit of the Quenched Hermitian Wilson-Dirac Operator
We investigate the approach to the continuum limit of the spectrum of the
Hermitian Wilson-Dirac operator in the supercritical mass region for pure gauge
SU(2) and SU(3) backgrounds. For this we study the spectral flow of the
Hermitian Wilson-Dirac operator in the range . We find that the
spectrum has a gap for and that the spectral density at zero,
, is non-zero for . We find that and, for
(exponential in the lattice spacing) as one goes to
the continuum limit. We also compute the topological susceptibility and the
size distribution of the zero modes. The topological susceptibility scales well
in the lattice spacing for both SU(2) and SU(3). The size distribution of the
zero modes does not appear to show a peak at a physical scale.Comment: 19 pages revtex with 9 postscript figures included by eps
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