779 research outputs found
Conformal Field Theory Correlators from Classical Scalar Field Theory on
We use the correspondence between scalar field theory on and a
conformal field theory on to calculate the 3- and 4-point functions of
the latter. The classical scalar field theory action is evaluated at tree
level.Comment: 9 pages, LaTeX2e with amsmath, amsfonts packages, section 2
rewritten, references adde
Using topic information to improve non-exact keyword-based search for mobile applications
Considering the wide offer of mobile applications available nowadays, effective search engines are imperative for an user to find applications that provide a specific desired functionality. Retrieval approaches that leverage topic similarity between queries and applications have shown promising results in previous studies. However, the search engines used by most app stores are based on keyword-matching and boosting. In this paper, we explore means to include topic information in such approaches, in order to improve their ability to retrieve relevant applications for non-exact queries, without impairing their computational performance. More specifically, we create topic models specialized on application descriptions and explore how the most relevant terms for each topic covered by an application can be used to complement the information provided by its description. Our experiments show that, although these topic keywords are not able to provide all the information of the topic model, they provide a sufficiently informative summary of the top- ics covered by the descriptions, leading to improved performance.info:eu-repo/semantics/publishedVersio
Anomalous Neutrino Reactions at HERA
We study the sensitivity of HERA to new physics using the helicity suppressed
reaction , where the final neutrino can be a standard
model one or a heavy neutrino. The approach is model independent and is based
on an effective lagrangian parametrization. It is shown that HERA will put
significant bounds on the scale of new physics, though, in general, these are
more modest than previously thought. If deviations from the standard model are
observed in the above processes, future colliders such as the SSC and LHC will
be able to directly probe the physics responsible for these discrepancies}Comment: 11 Pages + 2 figures is TOPDRAWER (included at the end or available
by mail). Report UCRHEP-T113 (requires the macropackage PHYZZX). A line in
the TeX file requesting an input file has been removed, it caused problem
Comparing Support Vector Machines with Gaussian Kernels to Radial Basis Function Classifiers
The Support Vector (SV) machine is a novel type of learning machine, based on statistical learning theory, which contains polynomial classifiers, neural networks, and radial basis function (RBF) networks as special cases. In the RBF case, the SV algorithm automatically determines centers, weights and threshold such as to minimize an upper bound on the expected test error. The present study is devoted to an experimental comparison of these machines with a classical approach, where the centers are determined by --means clustering and the weights are found using error backpropagation. We consider three machines, namely a classical RBF machine, an SV machine with Gaussian kernel, and a hybrid system with the centers determined by the SV method and the weights trained by error backpropagation. Our results show that on the US postal service database of handwritten digits, the SV machine achieves the highest test accuracy, followed by the hybrid approach. The SV approach is thus not only theoretically well--founded, but also superior in a practical application
Poincar\'{e} gauge theory of gravity
A Poincar\'{e} gauge theory of (2+1)-dimensional gravity is developed.
Fundamental gravitational field variables are dreibein fields and Lorentz gauge
potentials, and the theory is underlain with the Riemann-Cartan space-time. The
most general gravitational Lagrangian density, which is at most quadratic in
curvature and torsion tensors and invariant under local Lorentz transformations
and under general coordinate transformations, is given. Gravitational field
equations are studied in detail, and solutions of the equations for weak
gravitational fields are examined for the case with a static, \lq \lq spin"less
point like source. We find, among other things, the following: (1)Solutions of
the vacuum Einstein equation satisfy gravitational field equations in the
vacuum in this theory. (2)For a class of the parameters in the gravitational
Lagrangian density, the torsion is \lq \lq frozen" at the place where \lq \lq
spin" density of the source field is not vanishing. In this case, the field
equation actually agrees with the Einstein equation, when the source field is
\lq \lq spin"less. (3)A teleparallel theory developed in a previous paper is
\lq \lq included as a solution" in a limiting case. (4)A Newtonian limit is
obtainable, if the parameters in the Lagrangian density satisfy certain
conditions.Comment: 27pages, RevTeX, OCU-PHYS-15
Bounds on the electromagnetic interactions of excited spin-3/2 leptons
We discuss possible deviations from QED produced by a virtual excited
spin-3/2 lepton in the reaction . Data recorded
by the OPAL Collaboration at a c.m. energy are used to
establish bounds on the nonstandard-lepton mass and coupling strengths.Comment: Latex, 5 pages, 7 ps figures. To be published in Phys. Rev.
Finding rare objects and building pure samples: Probabilistic quasar classification from low resolution Gaia spectra
We develop and demonstrate a probabilistic method for classifying rare
objects in surveys with the particular goal of building very pure samples. It
works by modifying the output probabilities from a classifier so as to
accommodate our expectation (priors) concerning the relative frequencies of
different classes of objects. We demonstrate our method using the Discrete
Source Classifier, a supervised classifier currently based on Support Vector
Machines, which we are developing in preparation for the Gaia data analysis.
DSC classifies objects using their very low resolution optical spectra. We look
in detail at the problem of quasar classification, because identification of a
pure quasar sample is necessary to define the Gaia astrometric reference frame.
By varying a posterior probability threshold in DSC we can trade off sample
completeness and contamination. We show, using our simulated data, that it is
possible to achieve a pure sample of quasars (upper limit on contamination of 1
in 40,000) with a completeness of 65% at magnitudes of G=18.5, and 50% at
G=20.0, even when quasars have a frequency of only 1 in every 2000 objects. The
star sample completeness is simultaneously 99% with a contamination of 0.7%.
Including parallax and proper motion in the classifier barely changes the
results. We further show that not accounting for class priors in the target
population leads to serious misclassifications and poor predictions for sample
completeness and contamination. (Truncated)Comment: MNRAS accepte
Conformal Field Theory Correlators from Classical Field Theory on Anti-de Sitter Space II. Vector and Spinor Fields
We use the AdS/CFT correspondence to calculate CFT correlation functions of
vector and spinor fields. The connection between the AdS and boundary fields is
properly treated via a Dirichlet boundary value problem.Comment: 14 pages, LaTeX2e with amsmath,amsfonts packages; v2:interactions
section corrected, reference adde
Holonomy Transformation in the FRW Metric
In this work we investigate loop variables in Friedman-Robertson-Walker
spacetime. We analyze the parallel transport of vectors and spinors in several
paths in this spacetime in order to classify its global properties. The band
holonomy invariance is analysed in this background.Comment: 8 page
How Big Can Anomalous W Couplings Be?
Conventional wisdom has it that anomalous gauge-boson self-couplings can be
at most a percent or so in size. We test this wisdom by computing these
couplings at one loop in a generic renormalizable model of new physics. (For
technical reasons we consider the CP-violating couplings here, but our results
apply more generally.) By surveying the parameter space we find that the
largest couplings (several percent) are obtained when the new particles are at
the weak scale. For heavy new physics we compare our findings with expectations
based on an effective-lagrangian analysis. We find general patterns of induced
couplings which robustly reflect the nature of the underlying physics. We build
representative models for which the new physics could be first detected in the
anomalous gauge couplings.Comment: 40 pages, 11 figures, (dvi file and figures combined into a uuencoded
compressed file), (We correct an error in eq. 39 and its associated figure
(9). No changes at all to the text.), McGill-93/40, UQAM-PHE-93/03,
NEIPH-93-00
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