4,423 research outputs found
Sum rules for helicity amplitudes from BRS invariance
The BRS invariance of the electroweak gauge theory leads to relationships
between amplitudes with external massive gauge bosons and amplitudes where some
of these gauge bosons are replaced with their corresponding Nambu-Goldstone
bosons. Unlike the equivalence theorem, these identities are exact at all
energies. In this paper we discuss such identities which relate the process
to and production. By using
a general form-factor decomposition for , and amplitudes, these identities are
expressed as sum rules among scalar form factors. Because these sum rules may
be applied order by order in perturbation theory, they provide a powerful test
of higher order calculations. By using additional Ward-Takahashi identities we
find that the various contributions are divided into separately gauge-invariant
subsets, the sum rules applying independently to each subset. After a general
discussion of the application of the sum rules we consider the one-loop
contributions of scalar-fermions in the Minimal Supersymmetric Standard Model
as an illustration.Comment: 37 pages, including 16 figure
Probing the Weak Boson Sector in
We study possible deviations from the standard model in the reaction at a 500 GeV collider. As a photon source we use a
laser backscattered photon beam. We investigate the most general and vertices including operators up to
energy-dimension-six which are Lorentz invariant. These vertices require four
extra parameters; two are CP-conserving, and , and two are
CP-violating, and . We present analytical expressions of
the helicity amplitudes for the process for arbitrary
values of anomalous couplings. Assuming Standard Model values are actually
measured we present the allowed region in the () plane at the
90\% confidence level. We then show how the angular correlation of the
decay products can be used to extract detailed information on the anomalous
(especially CP-violating) and couplings.Comment: Latex, 25 pages, 12 figures (not included). One compressed postscript
file including all the figures available at
ftp://ftp.kek.jp/kek/preprints/TH/TH-420/kekth420.ps.g
Regge description of high energy pion pion total cross sections
We have recently presented a Regge description of pion-pion total cross
sections valid above 1.4 GeV, consistent with the few existing experiments,
factorization and crossing symmetry. In this note we show how it also describes
a further large data sample obtained from an analysis of experiments on
and .Comment: 3 pages. To appear in the proceedings of the MESON 2004 workshop,
Krakow, July 2004, to be published in Int. J. Mod. Phys.
Triviality and the Precision Bound on the Higgs Mass
The triviality of the scalar sector of the standard one-doublet Higgs model
implies that this model is only an effective low-energy theory valid below some
cut-off scale Lambda. For a heavy higgs this scale must be relatively low (10
TeV or less). Additional interactions coming from the underlying theory, and
suppressed by the scale Lambda, give rise to model-dependent corrections to
precisely measured electroweak quantities. Dimension six operators arising from
the underlying physics naturally contribute to the S and T parameters, and
their effects should be included in a global fit to the precision data that
determines any limit on the Higgs mass. Using dimensional analysis, we estimate
the expected size of these corrections in a custodially-symmetric
strongly-interacting underlying theory. Taking these operators' coefficients to
be of natural size gives sufficiently large contributions to the T parameter to
reconcile Higgs masses as large as 400-500 GeV with the precision data.Comment: 9 pages, 3 epsf figures include
Preliminary Results on gamma gamma -> Ks K pi from CLEO
We analyzed 13.8 fb^{-1} of the integrated e+e- luminosity collected at 10.6
GeV center-of-mass energy with the CLEO II and II.V detectors to study
exclusive two-photon production of single hadronic resonances. We searched for
hadrons decaying into Ks K pi when both leptons remain undetected. In this
analysis we studied the detection efficiency and evaluated systematic errors
using independent data samples. We estimated 90% CL upper limits on the
products of the two-photon partial widths of (pseudo)scalar hadrons with masses
below 1.7 GeV/c2 and their branching fractions into Ks K pi. Our preliminary
results are marginally consistent with the first observation of eta(1440) in
two-photon collisions by the L3 experiment.Comment: 4 pages, 1 figure, proceedings contribution for PANIC'0
Study Protocol for Investigating Physician Communication Behaviours that Link Physician Implicit Racial Bias and Patient Outcomes in Black Patients with Type 2 Diabetes Using an Exploratory Sequential Mixed Methods Design
Introduction Patient-physician racial discordance is associated with Black patient reports of dissatisfaction and mistrust, which in turn are associated with poor adherence to treatment recommendations and underutilisation of healthcare. Research further has shown that patient dissatisfaction and mistrust are magnified particularly when physicians hold high levels of implicit racial bias. This suggests that physician implicit racial bias manifests in their communication behaviours during medical interactions. The overall goal of this research is to identify physician communication behaviours that link physician implicit racial bias and Black patient immediate (patient-reported satisfaction and trust) and long-term outcomes (eg, medication adherence, self-management and healthcare utilisation) as well as clinical indicators of diabetes control (eg, blood pressure, HbA1c and history of diabetes complication). Methods and analysis Using an exploratory sequential mixed methods research design, we will collect data from approximately 30 family medicine physicians and 300 Black patients with type 2 diabetes mellitus. The data sources will include one physician survey, three patient surveys, medical interaction videos, video elicitation interviews and medical chart reviews. Physician implicit racial bias will be assessed with the physician survey, and patient outcomes will be assessed with the patient surveys and medical chart reviews. In video elicitation interviews, a subset of patients (approximately 20–40) will watch their own interactions while being monitored physiologically to identify evocative physician behaviours. Information from the interview will determine which physician communication behaviours will be coded from medical interactions videos. Coding will be done independently by two trained coders. A series of statistical analyses (zero-order correlations, partial correlations, regressions) will be conducted to identify physician behaviours that are associated significantly with both physician implicit racial bias and patient outcomes
Articulatory Tradeoffs Reduce Acoustic Variability During American English /r/ Production
Acoustic and articulatory recordings reveal that speakers utilize systematic articulatory tradeoffs to maintain acoustic stability when producing the phoneme /r/. Distinct articulator configurations used to produce /r/ in various phonetic contexts show systematic tradeoffs between the cross-sectional areas of different vocal tract sections. Analysis of acoustic and articulatory variabilities reveals that these tradeoffs act to reduce acoustic variability, thus allowing large contextual variations in vocal tract shape; these contextual variations in turn apparently reduce the amount of articulatory movement required. These findings contrast with the widely held view that speaking involves a canonical vocal tract shape target for each phoneme.National Institute on Deafness and Other Communication Disorders (1R29-DC02852-02, 5R01-DC01925-04, 1R03-C2576-0l); National Science Foundation (IRI-9310518
Powerful Water Masers in Active Galactic Nuclei
Luminous water maser emission in the 6_(16)-5_(23) line at 22 GHz has been
detected from two dozen galaxies. In all cases the emission is confined to the
nucleus and has been found only in AGN, in particular, in Type 2 Seyferts and
LINERs. I argue that most of the observed megamaser sources are powered by
X-ray irradiation of dense gas by the central engine. After briefly reviewing
the physics of these X-Ray Dissociation Regions, I discuss in detail the
observations of the maser disk in NGC 4258, its implications, and compare
alternative models for the maser emission. I then discuss the observations of
the other sources that have been imaged with VLBI to date, and how they do or
do not fit into the framework of a thin, rotating disk, as in NGC 4258.
Finally, I briefly discuss future prospects, especially the possibility of
detecting other water maser transitions.Comment: 45 pages, 16 figures. Refereed and greatly expanded version of my
review talk at the ASA meeting in Lorne, July 2001. To appear in Proceedings
of the Astronomical Society of Australi
Amplitude Zeros in Production
We demonstrate that the Standard Model amplitude for at the Born-level exhibits an approximate zero located at
at
high energies, where the () are the left-handed couplings
of the -boson to fermions and is the center of mass scattering
angle of the -boson. The approximate zero is the combined result of an exact
zero in the dominant helicity amplitudes and strong gauge
cancelations in the remaining amplitudes. For non-standard couplings
these cancelations no longer occur and the approximate amplitude zero is
eliminated.Comment: 11 pages, 4 figures submitted separately as uuencoded tar-ed
postscript files, FSU-HEP-940307, UCD-94-
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