113 research outputs found
Computing the Exact Radius of Large Graphs
No full textThe radius of a graph is an important structural parameter which plays a key role in social network analysis and related applications. It measures the minimum shortest path distance that is required to reach all nodes in the graph from a single node. A node from which all other nodes are within a distance equal to the radius is called a center of the graph. In a graph with n nodes and m edges, the center and the radius can be determined in Õ(nm) by computing shortest path distances between all pairs of nodes. Fine-grained complexity results suggest that asymptotically faster algorithms are unlikely to exist. In this paper, we describe a novel randomized algorithm for exact radius computation in weighted digraphs with an expected running time in Õ(d³m) where d is the so-called combinatorial dimension. Our methodology is inspired by Clarkson’s algorithm for LP-type problems. The value of d denotes the size of a basis, which is a smallest subset of nodes which enforce the same radius as the whole node set. While we show that there exist graphs with d ∈ Θ(n), our empirical analysis reveals that even large real-world graphs have small combinatorial dimension. This allows us to compute the radius in near-linear time on such instances. The significantly improved scalability can be clearly observed in our experimental evaluation on a diverse set of benchmark graphs
ATLAS QCD measurements for Higgs studies and New Physics searches
No full textUnderstanding of modelling of Standard Model processes plays an important role for Higgs physics and searches beyond the Standard Model. Measurements such as vector boson plus jet production are essential for the understanding of backgrounds, modelling of double parton interactions, heavy flavour production from gluon splitting and modelling of the underlying event. Precision QCD measurements can be also used to constrain parton density functions, which are important for understanding of the Higgs boson production cross section and the Standard Model backgrounds at the LHC kinematic limits. A review of recent ATLAS measurements is presented
Why Germany fell out of love with Europe
No full textThis essay analyses the central role that Germany has and continues to play in the European Union. The author looks back at how Germany acted as a Â?benevolent hegemonÂ? through the adoption of the single currency and the creation of the European Monetary Union. Against this background, he examines the German response to the recent euro crisis, in particular the crucial weekend of May 8-9 2010. He asks if Germany is still willing to be the benevolent hegemon and save the euro from disintegration, or are the domestic implications of this role moving her away from Europe.
Search for the Standard Model Higgs boson produced in association with vector bosons and decaying to using the ATLAS detector
No full textA new neutral boson decaying into pairs of photons and W or Z bosons with an invariant mass of ~ 125 GeV has been observed and requires confirmation of its coupling to fermions in order to determine whether it is the Standard Model (SM) Higgs boson. A vital observation would be its decay into quark pairs, which has a predicted branching ratio of 58% for = 125 GeV. This poster presents an updated direct search with the ATLAS experiment for decays of the Standard Model Higgs boson produced in association with a W or Z boson using 4.7 and 20.3 fb-1 of LHC proton-proton data at centre-of-mass energies of 7 and 8 TeV, respectively. The search is performed in the three decay modes , and with denoting either electrons or muons. No significant excess is observed. The observed (expected) 95% C.L. upper limit on the production cross section times the branching ratio for = 125 GeV is found to be 1.4 (1.3) times the SM prediction. The diboson production with is used to validate the analysis. The ratio of the observed Higgs (diboson) cross section to the SM expectation is found to be
Dijet Invariant Mass Studies in the Higgs boson H→bb- resonance search in association with a W/Z boson using the ATLAS detector
No full textThe Standard Model of Particle Physics describes the fundamental
building blocks of matter and phenomena up to the highest particle
interaction energies. The theory demands the existence of a scalar
particle: the Higgs boson. The Higgs boson was discovered by the
ATLAS and CMS collaborations at CERN using bosonic final states and
is measured to have a mass of around 125 GeV. This particle is predicted
to decay predominantly into pairs of b-quarks at this mass, but suffers
from overwhelming backgrounds from the multijet production expected
from QCD interactions. Therefore, H→bb- production in association
with a leptonically decaying W or Z boson is considered, with Z → vv-,
W → lv and Z → ll, where ` denotes electrons and muons.
This thesis presents a search for the Higgs boson decaying into bb-
pairs in association with a W or Z boson using the ATLAS detector
at the Large Hadron Collider (LHC) at CERN. The analysis uses the
full dataset recorded during pp collisions at the LHC in Run-1, corresponding
to 4.7 fb-1 at √s = 7 TeV and 20.3 fb-1 at √s = 8 TeV. A
multivariate technique and a kinematic cut-based approach have been
used to maximize the signal over background ratio, where a particular
emphasis on the latter approach is made in this thesis.
Final state radiation and reconstruction effects may decrease the
bb- resonance resolution significantly, while comparably decreasing the
probability of observing the decay over the background. The b quark
pairs from the Higgs boson are reconstructed as topological clusters
formed to jets in the ATLAS calorimeter. Thus, the reconstruction and
calibration of these jets are crucial for the final Higgs mass resolution
and paramount for the search and for future precision measurements
of V H, H→bb- production. This thesis presents the development and
evaluation of advanced techniques to improve the invariant dijet mass
reconstruction of the H→bb- candidate. Sequential jet calibrations,
semileptonic corrections and pT corrections to account for the interplay
between jet resolution/scale and the underlying signal pT spectrum
obtained from Monte Carlo simulations have been studied. A major
focus has been made on the development and evaluation of an event-level
kinematic likelihood fitting framework to exploit the full kinematic
potential of V H topologies within the detector uncertainties of the
reconstructed final state signatures in order to improve the measurement
of the b-tagged jet kinematics.
The jet energy calibrations of the H→bb- signal candidates yield
an overall improvement of the dijet invariant mass resolution of up
to ~30%, and of the expected statistical significance of ~12%. The
analysis procedure is validated using the resonant V Z(bb-) production
in the same final states as for the Higgs boson search, and is observed,
compatible with the Standard Model expectation, with a significance of
4.9 standard deviations and a signal strength of μ^V Z = 0:74+0:17
-0:16. For
a Higgs boson mass of 125.36 GeV, the observed (expected) deviation
from the background-only hypothesis is found with a significance of
1.4 (2.6) standard deviations and a signal strength is determined to be
μ^V H = 0:52±0:32(stat.)±0:24(syst.)
Coordinating users of shared facilities via data-driven predictive assistants and game theory
No full textCoordinating Users of Shared Facilities via Data-driven Predictive Assistants and Game Theory
No full textWe study data-driven assistants that provide congestion forecasts to users of shared facilities (roads, cafeterias, etc.), to support coordination between them, and increase efficiency of such collective systems. Key questions are: (1) when and how much can (accurate) predictions help for coordination, and (2) which assistant algorithms reach optimal predictions? First we lay conceptual ground for this setting where user preferences are a priori unknown and predictions influence outcomes. Addressing (1), we establish conditions under which self-fulfilling prophecies, i.e., "perfect" (probabilistic) predictions of what will happen, solve the coordination problem in the game-theoretic sense of selecting a Bayesian Nash equilibrium (BNE). Next we prove that such prophecies exist even in large-scale settings where only aggregated statistics about users are available. This entails a new (nonatomic) BNE existence result. Addressing (2), we propose two assistant algorithms that sequentially learn from users' reactions, together with optimality/convergence guarantees. We validate one of them in a large real-world experiment
Search for a CP-odd Higgs boson decaying to Zh in pp collisions at root s=8 TeV with the ATLAS detector
No full textSee paper for full list of authors – 13 pages plus author list + cover pages (30 pages total), 5 figures, 2 tables, submitted to Phys. Lett. B, All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HIGG-2013-06/International audienceA search for a heavy, CP-odd Higgs boson, , decaying into a boson and a 125 GeV Higgs boson, , with the ATLAS detector at the LHC is presented. The search uses proton--proton collision data at a centre-of-mass energy of 8 TeV corresponding to an integrated luminosity of 20.3 fb. Decays of CP-even bosons to or pairs with the boson decaying to electron or muon pairs are considered, as well as decays with the boson decaying to neutrinos. No evidence for the production of an boson in these channels is found and the 95% confidence level upper limits derived for \sigma (gg\rightarrow A) \times \mbox{BR}(A \rightarrow Zh) \times \mbox{BR}(h \rightarrow f\bar{f}) are 0.098--0.013 pb for and 0.57--0.014 pb for in a range of 220--1000 GeV. The results are combined and interpreted in the context of two-Higgs doublet models
"Can Portugal Escape Stagnation without Opting Out from the Eurozone?"
No full textThe creation of the Economic and Monetary Union (EMU) has not brought significant gains to the Portuguese economy in terms of real convergence with wealthier eurozone countries. We analyze the causes of the underperformance of the Portuguese economy in the last decade, discuss its growth prospects within the EMU, and make two proposals for urgent institutional reform of the EMU. We argue that, under the prevailing institutional framework, Portugal faces a long period of stagnation, high unemployment, and painful structural reform, and conclude that, in the absence of institutional reform of the EMU, getting out of the eurozone represents a serious political option for Portugal.Nominal Wage Cuts; Eurozone; Relative Unit Labor Costs; Zero-sum Game
Beyond the economics of the euro - analysing the institutional evolution of EMU 1999-2010, September 2011
No full textThis Occasional Paper examines how and why the institutional framework governing EMU has evolved since the creation of the euro. Building on theories of institutionalism, the paper in particular investigates to what extent functional spillovers from the single currency into other policy domains, like macroeconomic policies or financial regulation, met with an adequate institutional response, and to what extent the existing institutional framework conditioned the response to the financial crisis. The interaction between policy requirements and institutional capabilities is examined both in “ordinary times” (1999-2007) and under “crisis conditions” (2007-10). The paper uses a typology of change which helps to put into perspective both the resilience of the institutional framework of EMU and its capacity to adapt. In this respect, it allows for a better understanding and framing of the current reforms of EMU economic governance. It concludes that even though the crisis will accelerate institutional development, it will do so only gradually, as path dependence and an inbuilt bias towards incremental change will prevent policy-makers from pursuing a “clean slate” strategy. JEL Classification: E52, E31, D84EMU institutional architecture, historical institutionalism, institutional change., rational choice
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