Studies of top quark production with the ATLAS detector at the LHC

A review is presented of the most recent measurements of top quark strong and electroweak production performed by using data collected with the ATLAS detector in proton-proton collisions at sqrt(s) = 7 and 8 TeV at the Large Hadron Collider corresponding to integrated luminosities of up to about 4.7/fb and 20/fb, respectively.Comment: 9 pages, 15 figures, Contribution to Proceedings for Les Rencontres de Physique de la Vall\'ee d'Aoste, La Thuile, Vall\'ee d'Aoste, Italy, February 23rd - March 1st 2014. To be Published by Nuovo Cimento

Neutral and Non Neutral Shock Effects on Hedging, Investment and Debt.

By trading derivatives on the financial markets, a firm can hedge against the fluctuations of its internal funds, in order to better coordinate investment and financing decisions. This work shows how optimal investment, debt and hedging strategy can be strongly dependent on the mechanism linking the firm's internal funds to its returns on investment. In particular, when internal funds react to a prospective price change (neutral shock), investment and debt would be positively related; when internal funds react to a non neutral productivity shock, investment and debt would be either negatively related (no hedging) or unrelated (hedging).Hedging, investment, debt, volatility, productivity.

Orthogonal polynomial kernels and canonical correlations for Dirichlet measures

We consider a multivariate version of the so-called Lancaster problem of characterizing canonical correlation coefficients of symmetric bivariate distributions with identical marginals and orthogonal polynomial expansions. The marginal distributions examined in this paper are the Dirichlet and the Dirichlet multinomial distribution, respectively, on the continuous and the N-discrete d-dimensional simplex. Their infinite-dimensional limit distributions, respectively, the Poisson-Dirichlet distribution and Ewens's sampling formula, are considered as well. We study, in particular, the possibility of mapping canonical correlations on the d-dimensional continuous simplex (i) to canonical correlation sequences on the d+1-dimensional simplex and/or (ii) to canonical correlations on the discrete simplex, and vice versa. Driven by this motivation, the first half of the paper is devoted to providing a full characterization and probabilistic interpretation of n-orthogonal polynomial kernels (i.e., sums of products of orthogonal polynomials of the same degree n) with respect to the mentioned marginal distributions. We establish several identities and some integral representations which are multivariate extensions of important results known for the case d=2 since the 1970s. These results, along with a common interpretation of the mentioned kernels in terms of dependent Polya urns, are shown to be key features leading to several non-trivial solutions to Lancaster's problem, many of which can be extended naturally to the limit as $d\rightarrow\infty$.Comment: Published in at http://dx.doi.org/10.3150/11-BEJ403 the Bernoulli (http://isi.cbs.nl/bernoulli/) by the International Statistical Institute/Bernoulli Society (http://isi.cbs.nl/BS/bshome.htm

Computational inference beyond Kingman's coalescent

Full likelihood inference under Kingman's coalescent is a computationally challenging problem to which importance sampling (IS) and the product of approximate conditionals (PAC) method have been applied successfully. Both methods can be expressed in terms of families of intractable conditional sampling distributions (CSDs), and rely on principled approximations for accurate inference. Recently, more general Λ- and Ξ- coalescents have been observed to provide better modelling ts to some genetic data sets. We derive families of approximate CSDs for nite sites Λ- and Ξ-coalescents, and use them to obtain "approximately optimal" IS and PAC algorithms for Λ coalescents, yielding substantial gains in efficiency over existing methods

Using asymmetry observables to discover and distinguish Z' signals in top pair production with the lepton-plus-jets final state at the LHC

We study the sensitivity of top pair production with six-fermion decay at the LHC to the presence and nature of an underlying Z' boson, accounting for full tree-level Standard Model ttbar interference, with all intermediate particles allowed off-shell. We concentrate on the lepton-plus-jets final state and simulate experimental conditions, including kinematic requirements and top quark pair reconstruction in the presence of missing transverse energy and combinatorial ambiguity in jet-top assignment. We focus on the differential mass spectra of the cross section and asymmetry observables, especially demonstrating the use of the latter in probing the coupling structure of a new neutral resonance, in addition to cases in which the asymmetry forms a complementary discovery observable.Comment: 4 pages, proceedings contribution for Fourth Annual Large Hadron Collider Physics, 13-18 June 2016, Lund, Swede

Discriminating Z' signals in semileptonic top pair production at the LHC

We investigate the sensitivity of top pair production to the properties of different Beyond the Standard Model theories embedding a new neutral boson. We include six-fermion decay, and account for the full tree-level Standard Model ttbar interference, with all intermediate particles allowed off-shell. We focus on those observables best suited to the lepton-plus-jets final state at the LHC, and simulate the resulting experimental conditions, including kinematic requirements and top quark pair reconstruction in the presence of missing transverse energy and combinatorial ambiguity in quark-top assignment. In particular, we demonstrate the use of asymmetry observables to probe the coupling structure of a new neutral resonance, in addition to cases in which these asymmetries may even form complementary discovery observables in combination with the differential cross section.Comment: 4 pages, 1 figure, 1 table. arXiv admin note: substantial text overlap with arXiv:1610.0407

The effective strength of selection in random environment

We analyse a family of two-types Wright-Fisher models with selection in a random environment and skewed offspring distribution. We provide a calculable criterion to quantify the impact of different shapes of selection on the fate of the weakest allele, and thus compare them. The main mathematical tool is duality, which we prove to hold, also in presence of random environment (quenched and in some cases annealed), between the population's allele frequencies and genealogy, both in the case of finite population size and in the scaling limit for large size. Duality also yields new insight on properties of branching-coalescing processes in random environment, such as their long term behaviour.Comment: 36 pages; v2 corrects an error in the proof of Thm 3.

Inverted and mirror repeats in model nucleotide sequences

We analytically and numerically study the probabilistic properties of inverted and mirror repeats in model sequences of nucleic acids. We consider both perfect and non-perfect repeats, i.e. repeats with mismatches and gaps. The considered sequence models are independent identically distributed (i.i.d.) sequences, Markov processes and long range sequences. We show that the number of repeats in correlated sequences is significantly larger than in i.i.d. sequences and that this discrepancy increases exponentially with the repeat length for long range sequences.Comment: 12 pages, 6 figure

Archaeological site monitoring: UAV photogrammetry can be an answer

During archaeological excavations it is important to monitor the new excavated areas and findings day by day in order to be able to plan future excavation activities. At present, this daily activity is usually performed by using total stations, which survey the changes of the archaeological site: the surveyors are asked to produce day by day draft plans and sections which allow archaeologists to plan their future activities. The survey is realized during the excavations or just at the end of every working day and drawings have to be produced as soon as possible in order to allow the comprehension of the work done and to plan the activities for the following day. By using this technique, all the measurements, even those not necessary for the day after, have to be acquired in order to avoid a ‘loss of memory'. A possible alternative to this traditional approach is aerial photogrammetry, if the images can be acquired quickly and at a taken distance able to guarantee the necessary accuracy of a few centimeters. Today the use of UAVs (Unmanned Aerial Vehicles) can be considered a proven technology able to acquire images at distances ranging from 4 m up to 20 m: and therefore as a possible monitoring system to provide the necessary information to the archaeologists day by day. The control network, usually present at each archaeological site, can give the stable control points useful for orienting a photogrammetric block acquired by using an UAV equipped with a calibrated digital camera and a navigation control system able to drive the aircraft following a pre-planned flight scheme. Modern digital photogrammetric software can solve for the block orientation and generate a DSM automatically, allowing rapid orthophoto generation and the possibility of producing sections and plans. The present paper describes a low cost UAV system realized by the research group of the Politecnico di Torino and tested on a Roman villa archaeological site located in Aquileia (Italy), a well-known UNESCO WHL site. The results of automatic orientation and orthophoto production are described in terms of their accuracy and the completeness of information guaranteed for archaeological site excavation managemen