94,163 research outputs found
The strongest experimental constraints on SU(5)xU(1) supergravity models
We consider a class of well motivated string-inspired flipped
supergravity models which include four supersymmetry breaking scenarios:
no-scale, strict no-scale, dilaton, and special dilaton, such that only three
parameters are needed to describe all new phenomena . We show that the LEP precise measurements of the electroweak parameters
in the form of the variable, and the CLEOII allowed range for
\bsg are at present the most important experimental constraints on this class
of models. For m_t\gsim155\,(165)\GeV, the constraint (at
90(95)\%CL) requires the presence of light charginos
(m_{\chi^\pm_1}\lsim50-100\GeV depending on ). Since all sparticle
masses are proportional to , m_{\chi^\pm_1}\lsim100\GeV
implies: m_{\chi^0_1}\lsim55\GeV, m_{\chi^0_2}\lsim100\GeV, m_{\tilde
g}\lsim360\GeV, m_{\tilde q}\lsim350\,(365)\GeV, m_{\tilde
e_R}\lsim80\,(125)\GeV, m_{\tilde e_L}\lsim120\,(155)\GeV, and
m_{\tilde\nu}\lsim100\,(140)\GeV in the no-scale (dilaton) flipped
supergravity model. The \bsg constraint excludes a significant fraction of
the otherwise allowed region in the plane
(irrespective of the magnitude of the chargino mass), while future experimental
improvements will result in decisive tests of these models. In light of the
constraint, we conclude that the outlook for chargino and
selectron detection at LEPII and at HERA is quite favorable in this class of
models.Comment: CTP-TAMU-40/93, Latex, 13 pages, 10 figures (available as uuencoded
0.963MB file from [email protected]
Possible Suppression of Resonant Signals for Split-UED by Mixing at the LHC?
The mixing of the imaginary parts of the transition amplitudes of nearby
resonances via the breakdown of the Breit-Wigner approximation has been shown
to lead to potentially large modifications in the signal rates for new physics
at colliders. In the case of suppression, this effect may be significant enough
to lead to some new physics signatures being initially missed in searches at,
e.g., the LHC. Here we explore the influence of this `width mixing' on the
production of the nearly degenerate, level-2 Kaluza-Klein (KK) neutral gauge
bosons present in Split-UED. We demonstrate that in this particular case large
cross section modifications in the resonance region are necessarily absent and
explain why this is so based on the group theoretical structure of the SM.Comment: 10 pages, 2 figures; discussion and references adde
Splitting of Surface Plasmon Frequencies of Metal Particles in a Nematic Liquid Crystal
We calculate the effective dielectric function for a suspension of small
metallic particles immersed in a nematic liquid crystal (NLC) host. For a
random suspension of such particles in the dilute limit, we calculate the
effective dielectric tensor exactly and show that the surface plasmon
(SP)resonance of such particles splits into two resonances, polarized parallel
and perpendicular to the NLC director. At higher concentrations, we calculate
this splitting using a generalized Maxwell-Garnett approximation, which can
also be applied to a small metal particle coated with NLC. To confirm the
accuracy of the MGA for NLC-coated spheres, we also use the Discrete Dipole
Approximation. The calculated splitting is comparable to that observed in
recent experiments on NLC-coated small metal particlesComment: 11 pages, 2 figures. To be published in Appl. Phys. Let
First Constraints on SU(5)xU(1) Supergravity from Trilepton Searches at the Tevatron
We present the first constraints on the parameter space of
supergravity (in both no-scale and dilaton scenarios) which arise from the
recently announced limits on trilepton searches at the Tevatron. The trilepton
rate has been calculated for those points in parameter space which satisfy not
only the minimal theoretical and experimental LEP constraints, but also the
{\em combined} effect of the following indirect experimental constraints: (i)
the CLEO limits on the rate, (ii) the long-standing limit on the
anomalous magnetic moment of the muon, (iii) the non-observation of anomalous
muon fluxes in underground detectors (``neutrino telescopes"), and (iv) the
electroweak LEP high-precision measurements in the form of the
parameters. For m_t=150\GeV, the trilepton
constraint rules out some regions of parameter space with chargino masses as
high as m_{\chi^\pm_1}\approx105\GeV, although it is not possible to
establish a new absolute lower bound on the chargino mass. For m_t=170\GeV,
the simultaneous imposition of {\em all} of the above constraints excludes the
dilaton scenario completely, and leaves only a few allowed points in parameter
space in the no-scale scenario (with m_{\tilde q}\approx m_{\tilde
g}\lsim285\GeV). The five-fold increase in integrated luminosity expected in
the upcoming Tevatron run should probe some regions of parameter space with
chargino masses much beyond the reach of LEPII.Comment: 9 pages, 5 figures, latex. Figures available as 0.540MB uuencoded
file from [email protected]. CERN-TH.7107/93, CTP-TAMU-72/9
Determination of the Joint Confidence Region of Optimal Operating Conditions in Robust Design by Bootstrap Technique
Robust design has been widely recognized as a leading method in reducing
variability and improving quality. Most of the engineering statistics
literature mainly focuses on finding "point estimates" of the optimum operating
conditions for robust design. Various procedures for calculating point
estimates of the optimum operating conditions are considered. Although this
point estimation procedure is important for continuous quality improvement, the
immediate question is "how accurate are these optimum operating conditions?"
The answer for this is to consider interval estimation for a single variable or
joint confidence regions for multiple variables.
In this paper, with the help of the bootstrap technique, we develop
procedures for obtaining joint "confidence regions" for the optimum operating
conditions. Two different procedures using Bonferroni and multivariate normal
approximation are introduced. The proposed methods are illustrated and
substantiated using a numerical example.Comment: Two tables, Three figure
Triadic motifs and dyadic self-organization in the World Trade Network
In self-organizing networks, topology and dynamics coevolve in a continuous
feedback, without exogenous driving. The World Trade Network (WTN) is one of
the few empirically well documented examples of self-organizing networks: its
topology strongly depends on the GDP of world countries, which in turn depends
on the structure of trade. Therefore, understanding which are the key
topological properties of the WTN that deviate from randomness provides direct
empirical information about the structural effects of self-organization. Here,
using an analytical pattern-detection method that we have recently proposed, we
study the occurrence of triadic "motifs" (subgraphs of three vertices) in the
WTN between 1950 and 2000. We find that, unlike other properties, motifs are
not explained by only the in- and out-degree sequences. By contrast, they are
completely explained if also the numbers of reciprocal edges are taken into
account. This implies that the self-organization process underlying the
evolution of the WTN is almost completely encoded into the dyadic structure,
which strongly depends on reciprocity.Comment: 12 pages, 3 figures; Best Paper Award at the 6th International
Conference on Self-Organizing Systems, Delft, The Netherlands, 15-16/03/201
A novel ingress node design for video streaming over optical burst switching networks
This paper introduces a novel ingress node design which takes advantage of video data partitioning in order to deliver enhanced video streaming quality when using H.264/AVC codec over optical burst switching networks. Ns2 simulations show that the proposed scheme delivers improved video traffic quality without affecting other traffic, such as best effort traffic. Although the extra network load is comparatively small, the average gain in video PSNR was 5 dB over existing burst cloning schemes, with a maximum end-to-end delay of 17 ms, and jitter of less than 0.35 ms
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