1,424 research outputs found
Bounds on R-parity Violation from Resonant Slepton Production at the LHC
We consider the ATLAS and CMS searches for dijet resonances, as well as the
ATLAS search for like-sign dimuon pairs at the LHC with 7 TeV center of mass
energy. We interpret their exclusions in terms of bounds on the supersymmetric
R-parity violating parameter space. For this we focus on resonant slepton
production followed by the corresponding decay.Comment: 17 pages, 11 figures, 3 table
Principal Component Analysis with Noisy and/or Missing Data
We present a method for performing Principal Component Analysis (PCA) on
noisy datasets with missing values. Estimates of the measurement error are used
to weight the input data such that compared to classic PCA, the resulting
eigenvectors are more sensitive to the true underlying signal variations rather
than being pulled by heteroskedastic measurement noise. Missing data is simply
the limiting case of weight=0. The underlying algorithm is a noise weighted
Expectation Maximization (EM) PCA, which has additional benefits of
implementation speed and flexibility for smoothing eigenvectors to reduce the
noise contribution. We present applications of this method on simulated data
and QSO spectra from the Sloan Digital Sky Survey.Comment: Accepted for publication in PASP; v2 with minor updates, mostly to
bibliograph
Large Extra Dimension effects through Light-by-Light Scattering at the CERN LHC
Observing light-by-light scattering at the Large Hadron Collider (LHC) has
received quite some attention and it is believed to be a clean and sensitive
channel to possible new physics. In this paper, we study the diphoton
production at the LHC via the process through graviton exchange in the Large Extra
Dimension (LED) model. Typically, when we do the background analysis, we also
study the Double Pomeron Exchange (DPE) of production. We
compare its production in the quark-quark collision mode to the gluon-gluon
collision mode and find that contributions from the gluon-gluon collision mode
are comparable to the quark-quark one. Our result shows, for extra dimension
, with an integrated luminosity at the
14 TeV LHC, that diphoton production through graviton exchange can probe the
LED effects up to the scale for the forward
detector acceptance , respectively, where
, and .Comment: 25 pages. 7 figs. Change some grammatical error
Geometrically enhanced extraordinary magnetoresistance in semiconductor-metal hybrids
Extraordinary magnetoresistance (EMR) arises in hybrid systems consisting of semiconducting material with an embedded metallic inclusion. We have investigated such systems with the use of finite-element modeling, with our results showing good agreement to existing experimental data. We show that this effect can be dramatically enhanced by over four orders of magnitude as a result of altering the geometry of the conducting region. The significance of this result lies in its potential application to EMR magnetic field sensors utilizing more familiar semiconducting materials with nonoptimum material parameters, such as silicon. Our model has been extended further with a geometry based on the microstructure of the silver chalcogenides, consisting of a randomly sized and positioned metallic network with interspersed droplets. This model has shown a large and quasilinear magnetoresistance analogous to experimental findings
t-channel production of heavy charged leptons
We study the pair production of heavy charged exotic leptons at e+ e-
colliders in the SU(2)_L x SU(2)_I x U(1)_Y model. This gauge group is a
subgroup of the grand unification group E6; SU(2)_I commutes with the electric
charge operator, and the three corresponding gauge bosons are electrically
neutral. In addition to the standard photon and Z boson contributions, we also
include the contributions from extra neutral gauge bosons. A t-channel
contribution due to W_I-boson exchange, which is unsuppressed by mixing angles,
is quite important. We calculate the left-right and forward-backward
asymmetries, and discuss how to differentiate different models.Comment: Increased discussion of experimental signatures. Version accepted by
PR
Warped Phenomenology
We explore the phenomenology associated with the recently proposed localized
gravity model of Randall and Sundrum where gravity propagates in a
5-dimensional non-factorizable geometry and generates the 4-dimensional
weak-Planck scale hierarchy by an exponential function of the compactification
radius, called a warp factor. The Kaluza-Klein tower of gravitons which emerge
in this scenario have strikingly different properties than in the factorizable
case with large extra dimensions. We derive the form of the graviton tower
interactions with the Standard Model fields and examine their direct production
in Drell-Yan and dijet events at the Tevatron and LHC as well as the KK
spectrum line-shape at high-energy linear \epem colliders. In the case where
the first KK excitation is observed, we outline the procedure to uniquely
determine the parameters of this scenario. We also investigate the effect of KK
tower exchanges in contact interaction searches. We find that present
experiments can place meaningful constraints on the parameters of this model.Comment: 14 pages, LaTex, 3 fig
Higgsless Electroweak Symmetry Breaking in Warped Backgrounds: Constraints and Signatures
We examine the phenomenology of a warped 5-dimensional model based on
SU(2) SU(2) U(1) model which implements
electroweak symmetry breaking through boundary conditions, without the presence
of a Higgs boson. We use precision electroweak data to constrain the general
parameter space of this model. Our analysis includes independent and
gauge couplings, radiatively induced UV boundary gauge kinetic terms, and all
higher order corrections from the curvature of the 5-d space. We show that this
setup can be brought into good agreement with the precision electroweak data
for typical values of the parameters. However, we find that the entire range of
model parameters leads to violation of perturbative unitarity in gauge boson
scattering and hence this model is not a reliable perturbative framework.
Assuming that unitarity can be restored in a modified version of this scenario,
we consider the collider signatures. It is found that new spin-1 states will be
observed at the LHC and measurement of their properties would identify this
model. However, the spin-2 graviton Kaluza-Klein resonances, which are a
hallmark of the Randall-Sundrum model, are too weakly coupled to be detected.Comment: More detailed analysis, added references, 43 pages, 15 figures, LaTe
Much Ado About Leptoquarks: A Comprehensive Analysis
We examine the phenomenological implications of a 200 GeV leptoquark in light
of the recent excess of events at HERA. Given the relative predictions of
events rates in e^+p versus e^-p, we demonstrate that classes of leptoquarks
may be excluded, including those contained in E_6 GUT models. It is shown that
future studies with polarized beams at HERA could reveal the chirality of the
leptoquark fermionic coupling and that given sufficient luminosity in each
e^\pm_{L,R} channel the leptoquark quantum numbers could be determined. The
implications of 200-220 GeV leptoquarks at the Tevatron are examined. While
present Tevatron data most likely excludes vector leptoquarks and leptogluons
in this mass region, it does allow for scalar leptoquarks. We find that while
leptoquarks have little influence on Drell-Yan production, further studies at
the Main Injector are possible in the single production channel. We investigate
precision electroweak measurements as well as the process e^+e^-\to q\bar q at
LEP II and find they provide no further restrictions on these leptoquark
models. We then ascertain that cross section and polarization asymmetry
measurements at the NLC provide the only direct mechanism to determine the
leptoquark's electroweak quantum numbers. The single production of leptoquarks
in \gamma e collisions by both the backscattered laser and Weisacker-Williams
techniques at the NLC is also discussed. Finally, we demonstrate that we can
obtain successful coupling constant unification in models with leptoquarks,
both with or without supersymmetry. The supersymmetric case requires the GUT
group to be larger than SU(5) such as flipped SU(5)\times U(1)_X.Comment: Corrected single production cross section at Tevatron, updated atomic
parity violation constraints, 55 page
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