105 research outputs found
Diabetic Retinopathy Screening Using Computer Vision
6-pagesDiabetic Retinopathy (DR) is one of the main causes of blindness and visual impairment in
developed countries, stemming solely from diabetes mellitus. Current screening methods using fundus
images rely on the experience of the operator as they are manually examined. Automated methods based
on neural networks and other approaches have not provided sensitivity or specificity above 85%. This
work presents a computer vision based method that directly identifies hard exudates and dot
haemorrhages (DH) from 100 digital fundus images from a graded database of images using standard
computer vision techniques, and clinical observation and knowledge. Sensitivity and specificity in
diagnosis are 95-100% in both cases. Positive and negative prediction values (PPV, NPV) were 95-100%
for both cases. The overall method is general, computationally efficient and suitable for further clinical
trials to test both accuracy and the ability to the track DR status over time
Constraints on the pMSSM from LAT Observations of Dwarf Spheroidal Galaxies
We examine the ability for the Large Area Telescope (LAT) to constrain
Minimal Supersymmetric Standard Model (MSSM) dark matter through a combined
analysis of Milky Way dwarf spheroidal galaxies. We examine the Lightest
Supersymmetric Particles (LSPs) for a set of ~71k experimentally valid
supersymmetric models derived from the phenomenological-MSSM (pMSSM). We find
that none of these models can be excluded at 95% confidence by the current
analysis; nevertheless, many lie within the predicted reach of future LAT
analyses. With two years of data, we find that the LAT is currently most
sensitive to light LSPs (m_LSP < 50 GeV) annihilating into tau-pairs and
heavier LSPs annihilating into b-bbar. Additionally, we find that future LAT
analyses will be able to probe some LSPs that form a sub-dominant component of
dark matter. We directly compare the LAT results to direct detection
experiments and show the complementarity of these search methods.Comment: 24 pages, 9 figures, submitted to JCA
Rare top decays t -> c gamma, t -> c g and CKM unitarity
Top flavour-changing neutral decays are extremely suppressed within the
Standard Model (SM) by the GIM mechanism, but can reach observable rates in
some of its extensions. We compute the branching ratios for t -> c gamma and t
-> c g in minimal SM extensions where the addition of a vector-like up or down
quark singlet breaks the unitarity of the 3 x 3 Cabibbo-Kobayashi-Maskawa (CKM)
matrix. The maximum rates obtained indicate to what extent present experimental
data allow 3 x 3 CKM unitarity to be broken in these models, and are too small
to be observed in the near future. As a by-product, we reproduce the
calculation of these branching ratios in the SM, and with an improved set of
parameters we obtain values one order of magnitude smaller than the ones
usually quoted in the literature. We study the CP asymmetries between the decay
rates of the top quark and antiquark, which can be much larger than in the SM,
also as a consequence of the partial breaking of 3 x 3 CKM unitarity.Comment: LaTeX, 15 pages, 12 PS figures, minor changes. To be published in PL
Constraining Supergravity Scenarios through the Decay.
We evaluate the branching ratio BR() in the minimal
supersymmetric standard model (MSSM), determining the corresponding
phenomenological restrictions on two attractive supergravity scenarios, namely
minimal supergravity and a class of models with a natural solution to the
problem. We have included in the calculation some one--loop refinements that
have a substantial impact on the results. The numerical results show some
disagreements with part of the previous results in the literature, while they
are in agreement with others. For minimal supergravity the CLEO upper and lower
bounds put important restrictions on the scalar and gaugino masses in both
cases . For the other supergravity scenarios the relevant
CLEO bound is the upper one. It is stressed the fact that an eventual
improvement of the experimental bounds of order would strengthen the
restrictions on the MSSM dramatically. This would be enough to discard these
supergravity scenarios with if no discrepancy is found with the
standard model prediction, while for there will remain low-energy
windows.Comment: 13 pages + 8 figures included in a separate file, Latex, requires
psfig.sty. We have corrected a mistake affecting some figures and their
corresponding quotations in the text, as well as several misprints
The Intermediate Higgs
Two paradigms for the origin of electroweak superconductivity are a weakly
coupled scalar condensate, and a strongly coupled fermion condensate. The
former suffers from a finetuning problem unless there are cancelations to
radiative corrections, while the latter presents potential discrepancies with
precision electroweak physics. Here we present a framework for electroweak
symmetry breaking which interpolates between these two paradigms, and mitigates
their faults. As in Little Higgs theories, the Higgs is a pseudo-Nambu
Goldstone boson, potentially composite. The cutoff sensitivity of the one loop
top quark contribution to the effective potential is canceled by contributions
from additional vector-like quarks, and the cutoff can naturally be higher than
in the minimal Standard Model. Unlike the Little Higgs models, the cutoff
sensitivity from one loop gauge contributions is not canceled. However, such
gauge contributions are naturally small as long as the cutoff is below 6 TeV.
Precision electroweak corrections are suppressed relative to those of
Technicolor or generic Little Higgs theories. In some versions of the
intermediate scenario, the Higgs mass is computable in terms of the masses of
these additional fermions and the Nambu-Goldstone Boson decay constant. In
addition to the Higgs, new scalar and pseudoscalar particles are typically
present at the weak scale
The littlest Higgs model and Higgs boson associated production with top quark pair at high energy linear collider
In the parameter space allowed by the electroweak precision measurement data,
we consider the contributions of the new particles predicted by the littlest
Higgs() model to the Higgs boson associated production with top quark pair
in the future high energy linear collider(). We find that the
contributions mainly come from the new gauge bosons and . For
reasonable values of the free parameters, the absolute value of the relative
correction parameter can be significanly large,
which might be observed in the future experiment with .Comment: latex files, 13 pages, 3 figure
Chromomagnetic Dipole Moment of the Top Quark Revisited
We study the complete one-loop contributions to the chromagnetic dipole
moment of the top quark in the Standard Model, two Higgs doublet
models, topcolor assited technicolor models (TC2), 331 models and extended
models with a single extra dimension. We find that the SM predicts
and that the predictions of the other models are also
consitent with the constraints imposed on by low-energy
precision measurements.Comment: 20 pages, 5 figures, Updat
Combined analysis of Z' -> t tbar and Z' -> t tbar j production for vector resonance searches at LHC
We have implemented a code for Z' + n jets production in ALPGEN, with Z'
decays into several final states, including l+ l- and t tbar. The MLM
prescription is used for matching the matrix element with the parton shower,
including in this way the leading soft and collinear corrections. In order to
demonstrate its capabilities, we perform a combined analysis of Z' -> t tbar
and Z' -> t tbar j production for a heavy leptophobic gauge boson. It is found
that the effect of the extra jet cannot only be accounted for by a K factor
multiplying the leading-order cross section. In fact, the combined analysis for
Z' -> t tbar and Z' -> t tbar j presented improves the statistical significance
of the signal by 25% (8.55 sigma versus 6.77 sigma for a Z' mass of 1 TeV),
compared with the results of an inclusive analysis carried out on the same
sample of t tbar + t tbar j events.Comment: LaTeX 17 pages, 13 PS figure
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