Level rearrangement in exotic atoms and quantum dots

A presentation and a generalisation are given of the phenomenon of level rearrangement, which occurs when an attractive long-range potential is supplemented by a short-range attractive potential of increasing strength. This problem has been discovered in condensate-matter physics and has also been studied in the physics of exotic atoms. A similar phenomenon occurs in a situation inspired by quantum dots, where a short-range interaction is added to an harmonic confinement.Comment: 12 pages, 11 figures, RevTeX

Associated production of charged Higgs bosons and top quarks with POWHEG

The associated production of charged Higgs bosons and top quarks at hadron colliders is an important discovery channel to establish the existence of a non-minimal Higgs sector. Here, we present details of a next-to-leading order (NLO) calculation of this process using the Catani-Seymour dipole formalism and describe its implementation in POWHEG, which allows to match NLO calculations to parton showers. Numerical predictions are presented using the PYTHIA parton shower and are compared to those obtained previously at fixed order, to a leading order calculation matched to the PYTHIA parton shower, and to a different NLO calculation matched to the HERWIG parton shower with MC@NLO. We also present numerical predictions and theoretical uncertainties for various Two Higgs Doublet Models at the Tevatron and LHC.Comment: 36 page

L’invasion mondiale de Drosophila suzukii : être une espèce « cousine » d’un organisme-modèle aide-t-il réellement à établir un contrôle biologique ? Espoirs, désillusions et nouvelles perspectives

L’invasion récente et rapide de Drosophila suzukii en Europe et en Amérique du Nord a suscité de nombreuses études sur le terrain comme en laboratoire. Cette drosophile est en effet à la fois un ravageur important, du fait de son développement dans des fruits à maturité, et une « cousine » de l’espèce modèle Drosophila melanogaster dont la biologie et la génétique sont bien connues. Cet article s’appuie sur les données publiées par différentes équipes et sur des résultats préliminaires pour discuter de l’avancée des recherches et notamment des questions suivantes: en quoi nos connaissances sur D. melanogaster peuvent-elles ou non aider à comprendre et gérer l’invasion de D. suzukii ? Les résultats obtenus en condition de laboratoire avec cette espèce sont-ils représentatifs de sa biologie ? Comment mesurer l’impact écologique d’une espèce invasive si la niche qu’elle vient occuper est peu décrite localement en termes d’espèces présentes et de réseaux trophiques ? Cet article discute aussi des pistes et contraintes en termes de lutte biologique et de biocontrôleThe recent and rapid invasion of Europe and North-America by Drosophila suzukii has generated numerous laboratory and field studies since this fly species is an agricultural pest that causes economical losses by laying eggs and developing in ripening fruits, but also because of its relatedness with the model species Drosophila melanogaster whose biology and genetics are well described. This commentary is based on recent data published by different research groups as well as some of our own preliminary results. It discusses the state of research on D. suzukii and addresses the main following questions: can the wide knowledge on D. melanogaster help us to understand and manage the D. suzukii invasion and how? Are lab results on D. suzukii really informative on its biology? How can the ecological impact of an invasive species be evaluated if the ecological niche is poorly described in terms of biodiversity and trophic network? We also outline constraints for the biological control of this pest species and suggest new possible approaches for its long-term managemen

Single-top Wt-channel production matched with parton showers using the POWHEG method

We present results for the next-to-leading order calculation of single-top Wt-channel production interfaced to Shower Monte Carlo programs, implemented according to the POWHEG method. A comparison with MC@NLO is carried out. Results obtained using the PYTHIA shower are also shown and the effect of typical cuts is briefly discussed.Comment: 23 pages, 9 figure

b-Initiated processes at the LHC: a reappraisal

Several key processes at the LHC in the standard model and beyond that involve $b$ quarks, such as single-top, Higgs, and weak vector boson associated production, can be described in QCD either in a 4-flavor or 5-flavor scheme. In the former, $b$ quarks appear only in the final state and are typically considered massive. In 5-flavor schemes, calculations include $b$ quarks in the initial state, are simpler and allow the resummation of possibly large initial state logarithms of the type $\log \frac{{\cal Q}^2}{m_b^2}$ into the $b$ parton distribution function (PDF), ${\cal Q}$ being the typical scale of the hard process. In this work we critically reconsider the rationale for using 5-flavor improved schemes at the LHC. Our motivation stems from the observation that the effects of initial state logs are rarely very large in hadron collisions: 4-flavor computations are pertubatively well behaved and a substantial agreement between predictions in the two schemes is found. We identify two distinct reasons that explain this behaviour, i.e., the resummation of the initial state logarithms into the $b$-PDF is relevant only at large Bjorken $x$ and the possibly large ratios ${\cal Q}^2/m_b^2$'s are always accompanied by universal phase space suppression factors. Our study paves the way to using both schemes for the same process so to exploit their complementary advantages for different observables, such as employing a 5-flavor scheme to accurately predict the total cross section at NNLO and the corresponding 4-flavor computation at NLO for fully exclusive studies.Comment: Fixed typo in Eq. (A.10) and few typos in Eq. (C.2) and (C.3

Gaugino production in proton-proton collisions at a center-of-mass energy of 8 TeV

Motivated by hints for a light Standard Model-like Higgs boson and a shift in experimental attention towards electroweak supersymmetry particle production at the CERN LHC, we update in this paper our precision predictions at next-to-leading order of perturbative QCD matched to resummation at the next-to-leading logarithmic accuracy for direct gaugino pair production in proton-proton collisions with a center-of-mass energy of 8 TeV. Tables of total cross sections are presented together with the corresponding scale and parton density uncertainties for benchmark points adopted recently by the experimental collaborations, and figures are presented for up-to-date model lines attached to them. Since the experimental analyses are currently obtained with parton showers matched to multi-parton matrix elements, we also analyze the precision of this procedure by comparing invariant-mass and transverse-momentum distributions obtained in this way to those obtained with threshold and transverse-momentum resummation.Comment: 28 pages, 7 figures, 9 tables; version to appear in JHE

NLO QCD corrections to tW' and tZ' production in forward-backward asymmetry models

We consider Z' and W' models recently proposed to explain the top forward-backward asymmetry at the Tevatron. We present the next-to-leading order QCD corrections to associated production of such vector bosons together with top quarks at the Large Hadron Collider, for centre-of-mass energies of 7 and 8 TeV. The corrections are significant, modifying the total production cross-section by 30-50%. We consider the effects of the corrections on the top and vector-boson kinematics. The results are directly applicable to current experimental searches, for both the ATLAS and CMS collaborations.Comment: 62 pages, 13 figures, 36 tables. v3 Updated to correspond to Journal version and incorporate supplementary materia

Automation of one-loop QCD corrections

We present the complete automation of the computation of one-loop QCD corrections, including UV renormalization, to an arbitrary scattering process in the Standard Model. This is achieved by embedding the OPP integrand reduction technique, as implemented in CutTools, into the MadGraph framework. By interfacing the tool so constructed, which we dub MadLoop, with MadFKS, the fully automatic computation of any infrared-safe observable at the next-to-leading order in QCD is attained. We demonstrate the flexibility and the reach of our method by calculating the production rates for a variety of processes at the 7 TeV LHC.Comment: 64 pages, 12 figures. Corrected the value of m_Z in table 1. In table 2, corrected the values of cross sections in a.4 and a.5 (previously computed with mu=mtop/2 rather than mu=mtop/4). In table 2, corrected the values of NLO cross sections in b.3, b.6, c.3, and e.7 (the symmetry factor for a few virtual channels was incorrect). In sect. A.4.3, the labeling of the four-momenta was incorrec

Single hadron response measurement and calorimeter jet energy scale uncertainty with the ATLAS detector at the LHC

The uncertainty on the calorimeter energy response to jets of particles is derived for the ATLAS experiment at the Large Hadron Collider (LHC). First, the calorimeter response to single isolated charged hadrons is measured and compared to the Monte Carlo simulation using proton-proton collisions at centre-of-mass energies of sqrt(s) = 900 GeV and 7 TeV collected during 2009 and 2010. Then, using the decay of K_s and Lambda particles, the calorimeter response to specific types of particles (positively and negatively charged pions, protons, and anti-protons) is measured and compared to the Monte Carlo predictions. Finally, the jet energy scale uncertainty is determined by propagating the response uncertainty for single charged and neutral particles to jets. The response uncertainty is 2-5% for central isolated hadrons and 1-3% for the final calorimeter jet energy scale.Comment: 24 pages plus author list (36 pages total), 23 figures, 1 table, submitted to European Physical Journal