Measurements of isolated prompt photons in pp collisions at 7 TeV in ATLAS

Two recent measurements of the cross section for the inclusive production of isolated prompt photons in pp collisions at a center-of-mass energy sqrt(s) = 7 TeV are presented. The results are based on data collected in 2010 with the ATLAS detector at the Large Hadron Collider. The measurements cover the pseudorapidity ranges |eta(gamma)|<1.37 and 1.52<|eta(gamma)|<2.37 and the transverse energy range 15 < ET(gamma) < 400 GeV. The measured cross sections are compared to predictions from next-to-leading-order perturbative QCD calculations.Comment: 4 pages, 4 figures. To appear in the proceedings of DIS201

Lepton-Flavor-Violating tau decays at BaBar

We present the most recent searches for lepton-flavor-violating tau decays in BaBar. We find no evidence of tau decaying to three charged leptons or to a charged lepton and a neutral meson (KS, rho, phi, K*0, anti-K*0), and set upper limits on the corresponding branching fractions between 1.8 and 19 times 10-8 at 90% confidence level.Comment: 4 pages, 2 figures. To appear in the SUSY09 conference proceeding

Labour market characteristics and the burden of ageing : North America versus Europe

A transition from pay-as-you-go pension systems to more private funded systems is often suggested as a solution to finance pension systems threatened by ageing. This paper analyses alternative potential remedies linked to changes in labour market characteristics, within an international computable overlapping-generations model of the world economy. A prolongation of the working life of skilled or unskilled individuals, an increase in the demand of skills, a rise in the education levels and increased skilled or unskilled immigration have very different outcomes in North-America and in Europe. In the latter region, a postponement in the retirement age of unskilled individuals has the most beneficial effect in relieving the fiscal pressure on pensions systems, because the proportion of unskilled workers is relatively larger in Europe than in North-America. In North-America, where skilled labour is more abundant, an acceleration in skill-biased technical change has the biggest impact on pensions systems, as it raises the productivity of skilled workers.OLG-CGE Model, ageing, labour market, migration

Micro-Macro Analysis of Complex Networks

Complex systems have attracted considerable interest because of their wide range of applications, and are often studied via a \u201cclassic\u201d approach: study a specific system, find a complex network behind it, and analyze the corresponding properties. This simple methodology has produced a great deal of interesting results, but relies on an often implicit underlying assumption: the level of detail on which the system is observed. However, in many situations, physical or abstract, the level of detail can be one out of many, and might also depend on intrinsic limitations in viewing the data with a different level of abstraction or precision. So, a fundamental question arises: do properties of a network depend on its level of observability, or are they invariant? If there is a dependence, then an apparently correct network modeling could in fact just be a bad approximation of the true behavior of a complex system. In order to answer this question, we propose a novel micro-macro analysis of complex systems that quantitatively describes how the structure of complex networks varies as a function of the detail level. To this extent, we have developed a new telescopic algorithm that abstracts from the local properties of a system and reconstructs the original structure according to a fuzziness level. This way we can study what happens when passing from a fine level of detail (\u201cmicro\u201d) to a different scale level (\u201cmacro\u201d), and analyze the corresponding behavior in this transition, obtaining a deeper spectrum analysis. The obtained results show that many important properties are not universally invariant with respect to the level of detail, but instead strongly depend on the specific level on which a network is observed. Therefore, caution should be taken in every situation where a complex network is considered, if its context allows for different levels of observability

The Architecture of Complex Systems

A short review of the recent results and models of complex networks.Comment: 8 pages, 1 figure. To appear on "Interdisciplinary Applications of Ideas from Nonextensive Statistical Mechanics and Thermodynamics", Santa Fe Institute for Studies of Complexity. Oxford University Pres

Harmony in the Small-World

The Small-World phenomenon, popularly known as six degrees of separation, has been mathematically formalized by Watts and Strogatz in a study of the topological properties of a network. Small-worlds networks are defined in terms of two quantities: they have a high clustering coefficient C like regular lattices and a short characteristic path length L typical of random networks. Physical distances are of fundamental importance in the applications to real cases, nevertheless this basic ingredient is missing in the original formulation. Here we introduce a new concept, the connectivity length D, that gives harmony to the whole theory. D can be evaluated on a global and on a local scale and plays in turn the role of L and 1/C. Moreover it can be computed for any metrical network and not only for the topological cases. D has a precise meaning in term of information propagation and describes in an unified way both the structural and the dynamical aspects of a network: small-worlds are defined by a small global and local D, i.e. by a high efficiency in propagating information both on a local and on a global scale. The neural system of the nematode C. elegans, the collaboration graph of film actors, and the oldest U.S. subway system, can now be studied also as metrical networks and are shown to be small-worlds.Comment: 16 pages, 3 figures, accepted for publication in Physica

Is the Boston subway a small-world network ?

The mathematical study of the small-world concept has fostered quite some interest, showing that small-world features can be identified for some abstract classes of networks. However, passing to real complex systems, as for instance transportation networks, shows a number of new problems that make current analysis impossible. In this paper we show how a more refined kind of analysis, relying on transportation efficiency, can in fact be used to overcome such problems, and to give precious insights on the general characteristics of real transportation networks, eventually providing a picture where the small-world comes back as underlying construction principle.Comment: 5 pages, 1 figure. To appear in Physica A, in a special issue devoted to the Proceedings of the Conference "Horizons in Complex Systems", Messina (Italy), Dec.5-Dec.8 200