8,787 research outputs found
The lowest resonance in QCD from low--energy data
We show that a generalization of Chiral Perturbation Theory,
including a perturbative singlet scalar field, converges faster towards the
physical value of sensible low--energy observables. The physical mass and width
of the scalar particle are obtained through a simultaneous analysis of the pion
radius and the gamma gamma -> pi^0 pi^0 cross-section. Both values are
statistically consistent with the ones obtained by using Roy equations in pi-pi
scattering. In addition we find indications that the photon-photon-singlet
coupling is quite small.Comment: pdfLatex 15 pages, 3 figure
Insights into states from an effective perspective
We discuss the two photon coupling of the lightest scalar meson on the basis
of an extension of PT. Using low energy data on the pion form-factor and
the cross-sections as inputs, we find
. The smallness of the
result and the relative weight between its components,
, suggests that the scalar meson is mainly a state.Comment: 14 pages, 6 figures. Part of the paper rewritten and enlarged,
including a discussion on pi-pi phase shifts. Added reference
Managing network congestion with a Kohonen-based RED queue
The behaviour of the TCP AIMD algorithm is known to cause queue length
oscillations when congestion occurs at a router output link. Indeed, due to
these queueing variations, end-to-end applications experience large delay
jitter. Many studies have proposed efficient Active Queue Management (AQM)
mechanisms in order to reduce queue oscillations and stabilize the queue
length. These AQM are mostly improvements of the Random Early Detection (RED)
model. Unfortunately, these enhancements do not react in a similar manner for
various network conditions and are strongly sensitive to their initial setting
parameters. Although this paper proposes a solution to overcome the
difficulties of setting these parameters by using a Kohonen neural network
model, another goal of this study is to investigate whether cognitive
intelligence could be placed in the core network to solve such stability
problem. In our context, we use results from the neural network area to
demonstrate that our proposal, named Kohonen-RED (KRED), enables a stable queue
length without complex parameters setting and passive measurements.Comment: 8 pages, 9 figure
Vector Meson Masses in Chiral Perturbation Theory
We discuss the vector meson masses within the context of Chiral Perturbation
Theory performing an expansion in terms of the momenta, quark masses and 1/Nc.
We extend the previous analysis to include isospin breaking effects and also
include up to order . We discuss vector meson chiral perturbation theory
in some detail and present a derivation from a relativistic lagrangian. The
unknown coefficients are estimated in various ways. We also discuss the
relevance of electromagnetic corrections and the implications of the present
calculation for the determination of quark masses.Comment: 17 pages, LaTeX, 2 figures. Revised version to appear in Nuclear
Physics B. One reference added, some misprints, mainly in the appendix,
correcte
Unsupervised routine discovery in egocentric photo-streams
The routine of a person is defined by the occurrence of activities throughout
different days, and can directly affect the person's health. In this work, we
address the recognition of routine related days. To do so, we rely on
egocentric images, which are recorded by a wearable camera and allow to monitor
the life of the user from a first-person view perspective. We propose an
unsupervised model that identifies routine related days, following an outlier
detection approach. We test the proposed framework over a total of 72 days in
the form of photo-streams covering around 2 weeks of the life of 5 different
camera wearers. Our model achieves an average of 76% Accuracy and 68% Weighted
F-Score for all the users. Thus, we show that our framework is able to
recognise routine related days and opens the door to the understanding of the
behaviour of people
Effects of macroeconomic uncertainty on leverage for US non-financial firms
In this paper, we investigate the link between optimal level of leverage and macroeconomic uncertainty. Using the model of firm's value maximization, we show that as macroeconomic uncertainty increases, captured by an increase in the variability of industrial production or inflation, firms decrease their optimal levels of borrowing. We test this prediction on a panel of non-financial US firms drawn from the annual COMPUSTAT quarterly database covering the period 1990-2000 and find that as macroeconomic uncertainty increases, firms behave to decrease their levels of leverage. Our results are robust with respect to the inclusion of macroeconomic factors, such as interest rate, inflation, and index of leading indicators.
Can State Language Policies Distort Students' Demand for Higher Education?
This paper takes advantage of a recent policy experiment in Ukraine's secondary education system to study the effect of stricter requirements for proficiency in the state language on linguistic minority students’ demand for, as well as opportunities to pursue, further studies at the university level. The reform that we consider obligated all minority students, including those studying in public schools with a full cycle of education in minority languages, to take a standardized school exit test (which is also a university entry test) in Ukrainian, the state language, thus denying them previously granted access to translated tests. Using school-level data and employing the difference-in-difference estimator we find evidence that the reform resulted in a decline in the number of subjects taken by minority students at the school exit test. There was also a notable shift in the take-up of particular subjects, with fewer exams taken by minority students in more linguistically-demanding subjects such as History, Biology, and Geography, and more exams taken in foreign languages and Math. Overall, our results suggest some distortions in the accumulation of human capital by linguistic minority students induced by the language policy.language policy, economics of minorities, education, Ukraine
The Vector and Scalar Form Factors of the Pion to Two Loops
We calculate the vector and scalar form factors of the pion to two loops in
Chiral Perturbation Theory. We estimate the unknown O(p^6) constants using
resonance exchange. We make a careful comparison to the available data and
determine two O(p^4) constants rather precisely, and two O(p^6) constants less
precisely. We also use Chiral Perturbation Theory to two loops to extract in a
model--independent manner the charge radius of the pion from the available
data, and obtain \rpiV=0.437\pm 0.016 fm^2.Comment: Latex2e, JHEP.cls, 30 pages 5 figure
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