335 research outputs found
Electroweak Fits and Constraints on the Higgs Mass
The current status of the quantities entering into the global electroweak
fits is reviewed, highlighting changes since Summer 2003. These data include
the precision electroweak properties of the Z and W bosons, the top-quark mass
and the value of the electromagnetic coupling constant, at the scale of the Z
boson mass. Using these Z and W (high Q^2) data, the value of the Higss mass is
extracted, within the context of the Standard Model (SM). The consistency of
the data, and the overall agreement with the SM, are discussed.Comment: 8 pages, 5 postscript figure
Are there anomalous Z fermion couplings ?
The couplings of the fermions to the Z boson are of great importance in
establishing the validity of the Standard Model and in looking for physics
beyond it.
The couplings of the b-quark to the Z boson have been the subject of much
experimental study and theoretical interpretation. The apparent excess in the
value of \Rbbz, the ratio of the partial width of the Z boson to \bbbar to
its total hadronic width, above the Standard Model expectation reported a few
years ago has now become much less significant. However, the measurements of
the pole forward-backward asymmetry \Afbzb for b-quarks at the Z pole and of
the {\it polarisation parameter} \Ab, obtained using a polarised electron
beam, have improved considerably in accuracy.
The latest data are examined and values of the vector and axial-vector
b-quark and c-quark couplings to the Z are extracted. The left and right handed
couplings are also extracted. It is found that whereas the c-quark couplings
are compatible with the Standard Model, those of the b-quark data are only
compatible with the Standard Model at about the 1% level. In addition, the
individual lepton couplings are extracted and the hypothesis of {\it lepton
universality} is examined.
The sensitivity of the limits from electroweak fits to the Higgs boson mass
to these data is examined.Comment: 16 pages, 6 figures. Figure captions correcte
Precise bounds on the Higgs boson mass
We study the renormalization group evolution of the Higgs quartic coupling
and the Higgs mass in the Standard Model. The one loop
equation for is non linear and it is of the Riccati type which we
numerically and analytically solve in the energy range where
is the mass of the top quark and GeV. We find that
depending on the value of the solution for
may have singularities or zeros and become negative in the
former energy range so the ultra violet cut off of the standard model should be
below the energy where the zero or singularity of occurs. We find
that for the Standard Model is valid in
the whole range . We consider two cases of the Higgs mass
relation to the parameters of the standard model: (a) the effective potential
method and (b) the tree level mass relations. The limits for
correspond to the following Higgs mass relation GeV. We also plot the dependence of the ultra violet cut
off on the value of the Higgs mass. We analyze the evolution of the vacuum
expectation value of the Higgs field and show that it depends on the value of
the Higgs mass. The pattern of the energy behavior of the VEV is different for
the cases (a) and (b). The behavior of , and
indicates the existence of a phase transition in the standard model. For the
effective potential this phase transition occurs at the mass range
GeV and for the tree level mass relations at GeV.Comment: 14 pages, 7 figures. Expanded the discussion of the Higgs mass
relation between the parameters of the Standard Model. Included the method of
the Higgs effective potentia
Precision Electroweak Tests of the Standard Model
The present status of precision electroweak data is reviewed. These data
include measurements of e+e- -> f+fbar, taken at the Z resonance at LEP, which
are used to determine the mass and width of the Z boson. In addition,
measurements have also been made of the forward-backward asymmetries for
leptons and heavy quarks, and also the final state polarisation of the
tau-lepton. At SLAC, where the electron beam was polarised, measurements were
made of the left-right polarised asymmetry, A_LR, and the left-right
forward-backward asymmetries for b and c quarks.
The mass, MW, and width, GW, of the W boson have been measured at the
Tevatron and at LEP, and the mass of the top quark, Mt, has been measured at
the Tevatron. These data, plus other electroweak data, are used in global
electroweak fits in which various Standard Model parameters are determined. A
comparison is made between the results of the direct measurements of MW and Mt
with the indirect results coming from electroweak radiative corrections. Using
all precision electroweak data fits are also made to determine limits on the
mass of the Higgs boson. The influence on these limits of specific
measurements, particularly those which are somewhat inconsistent with the
Standard Model, is explored. The data are also analysed in terms of the quasi
model-independent epsilon variables.
Finally, the impact on the electroweak fits of the improvements in the
determination of the W-boson and top-quark masses, expected from the Tevatron
Run 2, is examined.Comment: 80 pages, 36 Figures, Late
Measurement of the Bottom-Strange Meson Mixing Phase in the Full CDF Data Set
We report a measurement of the bottom-strange meson mixing phase \beta_s
using the time evolution of B0_s -> J/\psi (->\mu+\mu-) \phi (-> K+ K-) decays
in which the quark-flavor content of the bottom-strange meson is identified at
production. This measurement uses the full data set of proton-antiproton
collisions at sqrt(s)= 1.96 TeV collected by the Collider Detector experiment
at the Fermilab Tevatron, corresponding to 9.6 fb-1 of integrated luminosity.
We report confidence regions in the two-dimensional space of \beta_s and the
B0_s decay-width difference \Delta\Gamma_s, and measure \beta_s in [-\pi/2,
-1.51] U [-0.06, 0.30] U [1.26, \pi/2] at the 68% confidence level, in
agreement with the standard model expectation. Assuming the standard model
value of \beta_s, we also determine \Delta\Gamma_s = 0.068 +- 0.026 (stat) +-
0.009 (syst) ps-1 and the mean B0_s lifetime, \tau_s = 1.528 +- 0.019 (stat) +-
0.009 (syst) ps, which are consistent and competitive with determinations by
other experiments.Comment: 8 pages, 2 figures, Phys. Rev. Lett 109, 171802 (2012
Genetic epidemiology of motor neuron disease-associated variants in the Scottish population
Genetic understanding of motor neuron disease (MND) has evolved greatly in the past 10Â years, including the recent identification of association between MND and variants in TBK1 and NEK1. Our aim was to determine the frequency of pathogenic variants in known MND genes and to assess whether variants in TBK1 and NEK1 contribute to the burden of MND in the Scottish population. SOD1, TARDBP, OPTN, TBK1, and NEK1 were sequenced in 441 cases and 400 controls. In addition to 44 cases known to carry a C9orf72 hexanucleotide repeat expansion, we identified 31 cases and 2 controls that carried a loss-of-function or pathogenic variant. Loss-of-function variants were found in TBK1 in 3 cases and no controls and, separately, in NEK1 in 3 cases and no controls. This study provides an accurate description of the genetic epidemiology of MND in Scotland and provides support for the contribution of both TBK1 and NEK1 to MND susceptibility in the Scottish population
In pursuit of visual attention: SSVEP frequency-tagging moving targets.
Previous research has shown that visual attention does not always exactly follow gaze direction, leading to the concepts of overt and covert attention. However, it is not yet clear how such covert shifts of visual attention to peripheral regions impact the processing of the targets we directly foveate as they move in our visual field. The current study utilised the co-registration of eye-position and EEG recordings while participants tracked moving targets that were embedded with a 30 Hz frequency tag in a Steady State Visually Evoked Potentials (SSVEP) paradigm. When the task required attention to be divided between the moving target (overt attention) and a peripheral region where a second target might appear (covert attention), the SSVEPs elicited by the tracked target at the 30 Hz frequency band were significantly, but transiently, lower than when participants did not have to covertly monitor for a second target. Our findings suggest that neural responses of overt attention are only briefly reduced when attention is divided between covert and overt areas. This neural evidence is in line with theoretical accounts describing attention as a pool of finite resources, such as the perceptual load theory. Altogether, these results have practical implications for many real-world situations where covert shifts of attention may discretely reduce visual processing of objects even when they are directly being tracked with the eyes
NEK1 variants confer susceptibility to amyotrophic lateral sclerosis
To identify genetic factors contributing to amyotrophic lateral sclerosis (ALS), we conducted whole-exome analyses of 1,022 index familial ALS (FALS) cases and 7,315 controls. In a new screening strategy, we performed gene-burden analyses trained with established ALS genes and identified a significant association between loss-of-function (LOF) NEK1 variants and FALS risk. Independently, autozygosity mapping for an isolated community in the Netherlands identified a NEK1 p.Arg261His variant as a candidate risk factor. Replication analyses of sporadic ALS (SALS) cases and independent control cohorts confirmed significant disease association for both p.Arg261His (10,589 samples analyzed) and NEK1 LOF variants (3,362 samples analyzed). In total, we observed NEK1 risk variants in nearly 3% of ALS cases. NEK1 has been linked to several cellular functions, including cilia formation, DNA-damage response, microtubule stability, neuronal morphology and axonal polarity. Our results provide new and important insights into ALS etiopathogenesis and genetic etiology
The Prevalence of Sexually Transmitted Infections in Papua New Guinea: A Systematic Review and Meta-Analysis
Patellofemoral osteoarthritis (PF OA) is more prevalent than previously thought and contributes to patient's suffering from knee OA. Synthesis of prevalence data can provide estimates of the burden of PF OA
TMEM106B is a genetic modifier of frontotemporal lobar degeneration with C9orf72 hexanucleotide repeat expansions
Hexanucleotide repeat expansions in chromosome 9 open reading frame 72 (C9orf72) have recently been linked to frontotemporal lobar degeneration (FTLD) and amyotrophic lateral sclerosis, and may be the most common genetic cause of both neurodegenerative diseases. Genetic variants at TMEM106B influence risk for the most common neuropathological subtype of FTLD, characterized by inclusions of TAR DNA-binding protein of 43 kDa (FTLD-TDP). Previous reports have shown that TMEM106B is a genetic modifier of FTLD-TDP caused by progranulin (GRN) mutations, with the major (risk) allele of rs1990622 associating with earlier age at onset of disease. Here, we report that rs1990622 genotype affects age at death in a single-site discovery cohort of FTLD patients with C9orf72 expansions (n = 14), with the major allele correlated with later age at death (p = 0.024). We replicate this modifier effect in a 30-site international neuropathological cohort of FTLD-TDP patients with C9orf72 expansions (n = 75), again finding that the major allele associates with later age at death (p = 0.016), as well as later age at onset (p = 0.019). In contrast, TMEM106B genotype does not affect age at onset or death in 241 FTLD-TDP cases negative for GRN mutations or C9orf72 expansions. Thus, TMEM106B is a genetic modifier of FTLD with C9orf72 expansions. Intriguingly, the genotype that confers increased risk for developing FTLD-TDP (major, or T, allele of rs1990622) is associated with later age at onset and death in C9orf72 expansion carriers, providing an example of sign epistasis in human neurodegenerative disease
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