1,054 research outputs found
Top asymmetry and the search for a light hadronic resonance in association with single top
The exchange of a light -channel flavor-changing gauge boson, \Vp, with
mass remains a leading explanation for the anomalous forward
backward asymmetry in top quark production at the Tevatron. Unlike other ideas,
including heavier -channel mediators, the light \Vp model is not easily
seen in the \mtt distribution. We advocate a more promising strategy. While
current analyses at hadron colliders may not be sensitive, we propose searching
for a resonance in association with single top that may allow discovery in
existing data. Deviations in the lepton charge asymmetry in this sample should
also be present.Comment: 5 pages, 2 figur
Top quark asymmetry and dijet resonances
CDF recently reported an anomaly in the distribution of dijet events
produced in association with a boson. If this anomaly is associated with a
new flavor conserving vector resonance, , one might have expected to observe
effects in the analogous distribution produced in association with a
. No such excess is observed. A single flavor changing
coupling, however, can contribute to the anomaly while being
consistent with other resonance searches. Furthermore, it gives a potential
explanation of the observed forward-backward asymmetry in top quark production.Comment: 4 pages, 1 figur
Top quark forward-backward asymmetry from new t-channel physics
Motivated by recent measurements of the top quark forward-backward asymmetry
at the Tevatron, we study how t-channel new physics can contribute to a large
value. We concentrate on a theory with an abelian gauge boson possessing flavor
changing couplings between up and top quarks, but satisfies flavor physics
constraints. Collider constraints are strong, but can be consistent with the
aid of small flavor diagonal couplings. We find that M_Z' ~ 160 GeV can yield a
total lab-frame asymmetry of ~18% without being in conflict with other
observables. There are implications for future collider searches, including
exotic top quark decays, like-sign top quark production, and detailed
measurements of the top production cross section. An alternate model with a
gauged non-Abelian flavor symmetry would have similar phenomenology, but lacks
the like-sign top signal.Comment: 5 pages, 4 figure
Top quark asymmetry from a non-Abelian horizontal symmetry
Motivated by the persistence of a large measured top quark forward-backward
asymmetry at the Tevatron, we examine a model of non-Abelian flavor gauge
symmetry. The exchange of the gauge bosons in the -channel can give a large
asymmetry due to the forward Rutherford scattering peak. We address generic
constraints on non-Abelian -channel physics models including flavor diagonal
resonances and potentially dangerous contributions to inclusive top pair cross
sections. We caution on the general difficulty of comparing theoretical
predictions for top quark signals to the existing experimental results due to
potentially important acceptance effects. The first signature at the Large
Hadron Collider can be a large inclusive top pair cross section, or like-sign
dilepton events, although the latter signal is much smaller than in Abelian
models. Deviations of the invariant mass distributions at the LHC will also be
promising signatures. A more direct consistency check of the Tevatron asymmetry
through the LHC asymmetry is more likely to be relevant at a later stage.Comment: 21 pages, 7 figure
Sound propagation over uneven ground and irregular topography
The goal of this research is to develop theoretical, computational, and experimental techniques for predicting the effects of irregular topography on long range sound propagation in the atmosphere. Irregular topography here is understood to imply a ground surface that is not idealizable as being perfectly flat or that is not idealizable as having a constant specific acoustic impedance. The interest of this study focuses on circumstances where the propagation is similar to what might be expected for noise from low-attitude air vehicles flying over suburban or rural terrain, such that rays from the source arrive at angles close to grazing incidence. The activities and developments that have resulted during the period, August 1986 through February 1987, are discussed
Reexamining Student-Athlete GPA: Traditional vs. Athletic Variables
A sample of 674 first-year student-athletes at a midsize Midwestern university were examined each year over a five-year period (2004–2008) to determine if athletic variables were powerful enough to be used in conjunction with traditional predictors of college success to predict GPA. The four specific athletic variables unique to student-athletes (i.e., sport, coaching change, playing time, team winning percentage), were hypothesized to be as predictive as traditional variables. Pearson correlations revealed student-athletes were more likely to earn a high first-year GPA if they were female (r = .35), Caucasian (r = -.33), scored well on standardized tests (r = -.47), had a respectable high school GPA (r = .64), were ranked high in their graduating high school class (r = -.58), had a relatively large high school graduating class (r = .15) were not undecided about major (r = -.11), were not a member of a revenue sport (r = .33), and earned a considerable amount of playing time in their first year (r = -.15). Least squares linear regression demonstrated the traditional variables of gender (B = .16), race (B = -.26), standardized test scores (B = .03), high school GPA (B = .41), high school rank (B < -.01), and size of high school graduating class (B < .01) were most influential in predicting first-year student-athlete GPA
Vascular regeneration in a basal chordate is due to the presence of immobile, bi-functional cells.
The source of tissue turnover during homeostasis or following injury is usually due to proliferation of a small number of resident, lineage-restricted stem cells that have the ability to amplify and differentiate into mature cell types. We are studying vascular regeneration in a chordate model organism, Botryllus schlosseri, and have previously found that following surgical ablation of the extracorporeal vasculature, new tissue will regenerate in a VEGF-dependent process within 48 hrs. Here we use a novel vascular cell lineage tracing methodology to assess regeneration in parabiosed individuals and demonstrate that the source of regenerated vasculature is due to the proliferation of pre-existing vascular resident cells and not a mobile progenitor. We also show that these cells are bi-potential, and can reversibly adopt two fates, that of the newly forming vessels or the differentiated vascular tissue at the terminus of the vasculature, known as ampullae. In addition, we show that pre-existing vascular resident cells differentially express progenitor and differentiated cell markers including the Botryllus homologs of CD133, VEGFR-2, and Cadherin during the regenerative process
Sound propagation over uneven ground and irregular topography
Theoretical, computational, and experimental techniques were developed for predicting the effects of irregular topography on long range sound propagation in the atmosphere. Irregular topography is understood to imply a ground surface that: (1) is not idealizable as being perfectly flat, or (2) that is not idealizable as having a constant specific acoustic impedance. The focus is on circumstances where the propagation is similar to what might be expected for noise from low altitude air vehicles flying over suburban or rural terrain, such that rays from the source arrive at angles close to grazing incidence
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