The lowest resonance in QCD from low--energy data

We show that a generalization of $su(2)$ 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 Q2Qˉ2Q^2 \bar{Q}^2 states from an effective perspective

We discuss the two photon coupling of the lightest scalar meson on the basis of an extension of $\chi$PT. Using low energy data on the pion form-factor and the $\gamma\gamma\to \pi^+\pi^-(\pi^0\pi^0)$ cross-sections as inputs, we find $\Gamma(\sigma\to\gamma\gamma) \cong 0.126~\rm{keV}$. The smallness of the result and the relative weight between its components, ${\Gamma_{\gamma\gamma\to S_1}\over \Gamma{ \gamma\gamma\to\pi\pi\to S_1}} < 1$, suggests that the scalar $0^{++}$ meson is mainly a $Q^2\bar{Q}^2$ 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 $p^4$. 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.

Small-Scale Business Survival and Inheritance: Evidence from Germany

In this paper we investigate whether small-scale businesses face financial constraints that affect their survival. We develop a model of moral hazard in which financial constraints arise endogenously. The model predicts that higher private assets relax financial constraints and have a positive effect on the firm's probability of survival. We test this proposition using German Socio-Economic Panel (GSOEP) data, which cover the period 1984-2004. The release from financial constraints is measured by inheritance. The empirical analysis confirms that the entrepreneur has a higher propensity to stay in business when she inherits capital. This effect is particularly strong for entrepreneurs that switch from self-employment into wage employment. These results are consistent with hypothesis that financial frictions have a perceptible impact on bankruptcy among small business firms.Entrepreneurship, survival, financial constraints

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