793 research outputs found
Light Stop Decays: Implications for LHC Searches
We investigate the flavour-changing neutral current decay of the lightest
stop into a charm quark and the lightest neutralino and its four-body decay
into the lightest neutralino, a down-type quark and a fermion pair. These are
the relevant stop search channels in the low-mass region. The SUSY-QCD
corrections to the two-body decay have been calculated for the first time and
turn out to be sizeable. In the four-body decay both the contributions from
diagrams with flavour-changing neutral current (FCNC) couplings and the mass
effects of final state bottom quarks and leptons have been taken into
account, which are not available in the literature so far. The resulting
branching ratios are investigated in detail. We find that in either of the
decay channels the branching ratios can deviate significantly from one in large
parts of the allowed parameter range. Taking this into account, the
experimental exclusion limits on the stop, which are based on the assumption of
branching ratios equal to one, are considerably weakened. This should be taken
into account in future searches for light stops at the next run of the LHC,
where the probed low stop mass region will be extended
The measurement of the Higgs self-coupling at the LHC: theoretical status
Now that the Higgs boson has been observed by the ATLAS and CMS experiments
at the LHC, the next important step would be to measure accurately its
properties to establish the details of the electroweak symmetry breaking
mechanism. Among the measurements which need to be performed, the determination
of the Higgs self-coupling in processes where the Higgs boson is produced in
pairs is of utmost importance. In this paper, we discuss the various processes
which allow for the measurement of the trilinear Higgs coupling: double Higgs
production in the gluon fusion, vector boson fusion, double Higgs-strahlung and
associated production with a top quark pair. We first evaluate the production
cross sections for these processes at the LHC with center-of-mass energies
ranging from the present TeV to TeV, and discuss
their sensitivity to the trilinear Higgs coupling. We include the various
higher order QCD radiative corrections, at next-to-leading order for gluon and
vector boson fusion and at next-to-next-to-leading order for associated double
Higgs production with a gauge boson. The theoretical uncertainties on these
cross sections are estimated. Finally, we discuss the various channels which
could allow for the detection of the double Higgs production signal at the LHC
and the accuracy on the self-coupling that could be ultimately achieved.Comment: 37 pages, 10 tables, 17 figures. Typos corrected, matches the journal
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Doping-dependent evolution of low-energy excitations and quantum phase transitions within effective model for High-Tc copper oxides
In this paper a mean-field theory for the spin-liquid paramagnetic
non-superconducting phase of the p- and n-type High- cuprates is
developed. This theory applied to the effective model with the
{\it ab initio} calculated parameters and with the three-site correlated
hoppings. The static spin-spin and kinematic correlation functions beyond
Hubbard-I approximation are calculated self-consistently. The evolution of the
Fermi surface and band dispersion is obtained for the wide range of doping
concentrations . For p-type systems the three different types of behavior
are found and the transitions between these types are accompanied by the
changes in the Fermi surface topology. Thus a quantum phase transitions take
place at and at . Due to the different Fermi surface topology
we found for n-type cuprates only one quantum critical concentration, .
The calculated doping dependence of the nodal Fermi velocity and the effective
mass are in good agreement with the experimental data.Comment: 8 page
Time-course analysis of genome-wide gene expression data from hormone-responsive human breast cancer cells
<p>Abstract</p> <p>Background</p> <p>Microarray experiments enable simultaneous measurement of the expression levels of virtually all transcripts present in cells, thereby providing a âmolecular pictureâ of the cell state. On the other hand, the genomic responses to a pharmacological or hormonal stimulus are dynamic molecular processes, where time influences gene activity and expression. The potential use of the statistical analysis of microarray data in time series has not been fully exploited so far, due to the fact that only few methods are available which take into proper account temporal relationships between samples.</p> <p>Results</p> <p>We compared here four different methods to analyze data derived from a time course mRNA expression profiling experiment which consisted in the study of the effects of estrogen on hormone-responsive human breast cancer cells. Gene expression was monitored with the innovative Illumina BeadArray platform, which includes an average of 30-40 replicates for each probe sequence randomly distributed on the chip surface. We present and discuss the results obtained by applying to these datasets different statistical methods for serial gene expression analysis. The influence of the normalization algorithm applied on data and of different parameter or threshold choices for the selection of differentially expressed transcripts has also been evaluated. In most cases, the selection was found fairly robust with respect to changes in parameters and type of normalization. We then identified which genes showed an expression profile significantly affected by the hormonal treatment over time. The final list of differentially expressed genes underwent cluster analysis of functional type, to identify groups of genes with similar regulation dynamics.</p> <p>Conclusions</p> <p>Several methods for processing time series gene expression data are presented, including evaluation of benefits and drawbacks of the different methods applied. The resulting protocol for data analysis was applied to characterization of the gene expression changes induced by estrogen in human breast cancer ZR-75.1 cells over an entire cell cycle.</p
Quantitative expression profiling of highly degraded RNA from formalin-fixed, paraffin-embedded breast tumor biopsies by oligonucleotide microarrays.
Microarray-based gene expression profiling is well suited for parallel quantitative analysis of large numbers of RNAs, but its application to cancer biopsies, particularly formalin-fixed, paraffin-embedded (FFPE) archived tissues, is limited by the poor quality of the RNA recovered. This represents a serious drawback, as FFPE tumor tissue banks are available with clinical and prognostic annotations, which could be exploited for molecular profiling studies, provided that reliable analytical technologies are found. We applied and evaluated here a microarray-based cDNA-mediated annealing, selection, extension and ligation (DASL) assay for analysis of 502 mRNAs in highly degraded total RNA extracted from cultured cells or FFPE breast cancer (MT) biopsies. The study included quantitative and qualitative comparison of data obtained by analysis of the same RNAs with genome-wide oligonucleotide microarrays vs DASL arrays and, by DASL, before and after extensive in vitro RNA fragmentation. The DASL-based expression profiling assay applied to RNA extracted from MCF-7 cells, before or after 24 h stimulation with a mitogenic dose of 17b-estradiol, consistently allowed to detect hormone-induced gene expression changes following extensive RNA degradation in vitro. Comparable results where obtained with tumor RNA extracted from FFPE MT biopsies (6 to 19 years old). The method proved itself sensitive, reproducible and accurate, when compared to results obtained by microarray analysis of RNA extracted from snap-frozen tissue of the same tumor
Probing for Invisible Higgs Decays with Global Fits
We demonstrate by performing a global fit on Higgs signal strength data that
large invisible branching ratios Br_{inv} for a Standard Model (SM) Higgs
particle are currently consistent with the experimental hints of a scalar
resonance at the mass scale m_h ~ 124 GeV. For this mass scale, we find
Br_{inv} < 0.64 (95 % CL) from a global fit to individual channel signal
strengths supplied by ATLAS, CMS and the Tevatron collaborations. Novel tests
that can be used to improve the prospects of experimentally discovering the
existence of a Br_{inv} with future data are proposed. These tests are based on
the combination of all visible channel Higgs signal strengths, and allow us to
examine the required reduction in experimental and theoretical errors in this
data that would allow a more significantly bounded invisible branching ratio to
be experimentally supported. We examine in some detail how our conclusions and
method are affected when a scalar resonance at this mass scale has couplings
deviating from the SM ones.Comment: 32pp, 15 figures v2: JHEP version, ref added & comment added after
Eq.
Theory of imaging a photonic crystal with transmission near-field optical microscopy
While near-field scanning optical microscopy (NSOM) can provide optical
images with resolution much better than the diffraction limit, analysis and
interpretation of these images is often difficult. We present a theory of
imaging with transmission NSOM that includes the effects of tip field,
tip/sample coupling, light propagation through the sample and light collection.
We apply this theory to analyze experimental NSOM images of a nanochannel glass
(NCG) array obtained in transmission mode. The NCG is a triangular array of
dielectric rods in a dielectric glass matrix with a two-dimensional photonic
band structure. We determine the modes for the NCG photonic crystal and
simulate the observed data. The calculations show large contrast at low
numerical aperture (NA) of the collection optics and detailed structure at high
NA consistent with the observed images. We present calculations as a function
of NA to identify how the NCG photonic modes contribute to and determine the
spatial structure in these images. Calculations are presented as a function of
tip/sample position, sample index contrast and geometry, and aperture size to
identify the factors that determine image formation with transmission NSOM in
this experiment.Comment: 28 pages of ReVTex, 14 ps figures, submitted to Phys. Rev.
Relation of Diabetes to Cognitive Function in Hispanics/Latinos of Diverse Backgrounds in the United States
Objectives:To examine the association between diabetes and cognitive function within U.S. Hispanics/Latinos of Central American, Cuban, Dominican, Mexican, Puerto Rican, and South American background. Method: This cross-sectional study included 9,609 men and women (mean age = 56.5 years), who are members of the Hispanic Community Health Study/Study of Latinos. We classified participants as having diabetes, prediabetes, or normal glucose regulation. Participants underwent a neurocognitive battery consisting of tests of verbal fluency, delayed recall, and processing speed. Analyses were stratified by Hispanic/Latino subgroup. Results: From fully adjusted linear regression models, compared with having normal glucose regulation, having diabetes was associated with worse processing speed among Cubans (ÎČ = â1.99; 95% CI [confidence interval] = [â3.80, â0.19]) and Mexicans (ÎČ = â2.26; 95% CI = [â4.02, â0.51]). Compared with having normal glucose regulation, having prediabetes or diabetes was associated with worse delayed recall only among Mexicans (prediabetes: ÎČ = â0.34; 95% CI = [â0.63, â0.05] and diabetes: ÎČ = â0.41; 95% CI = [â0.79, â0.04]). No associations with verbal fluency. Discussion: The relationship between diabetes and cognitive function varied across Hispanic/Latino subgroup
Fellows as teachers: a model to enhance pediatric resident education
Pressures on academic faculty to perform beyond their role as educators has stimulated interest in complementary approaches in resident medical education. While fellows are often believed to detract from resident learning and experience, we describe our preliminary investigations utilizing clinical fellows as a positive force in pediatric resident education. Our objectives were to implement a practical approach to engage fellows in resident education, evaluate the impact of a fellow-led education program on pediatric resident and fellow experience, and investigate if growth of a fellowship program detracts from resident procedural experience.This study was conducted in a neonatal intensive care unit (NICU) where fellows designed and implemented an education program consisting of daily didactic teaching sessions before morning clinical rounds. The impact of a fellow-led education program on resident satisfaction with their NICU experience was assessed via anonymous student evaluations. The potential value of the program for participating fellows was also evaluated using an anonymous survey.The online evaluation was completed by 105 residents. Scores were markedly higher after the program was implemented in areas of teaching excellence (4.44 out of 5 versus 4.67, p<0.05) and overall resident learning (3.60 out of 5 versus 4.61, p<0.001). Fellows rated the acquisition of teaching skills and enhanced knowledge of neonatal pathophysiology as the most valuable aspects of their participation in the education program. The anonymous survey revealed that 87.5% of participating residents believed that NICU fellows were very important to their overall training and education.While fellows are often believed to be a detracting factor to residency training, we found that pediatric resident attitudes toward the fellows were generally positive. In our experience, in the specialty of neonatology a fellow-led education program can positively contribute to both resident and fellow learning and satisfaction. Further investigation into the value of utilizing fellows as a positive force in resident education in other medical specialties appears warranted
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