Study of the Wtb vertex structure at the ATLAS experiment

The top quark is the heaviest and least studied quark of the Standard Model. Although its properties have already been investigated at colliders, the statistics of the collected data have not yet allowed for precise measurements, with exception of its mass. The determination of other fundamental properties such as its couplings requires larger top quark samples, which will be available at the Large Hadron Collider (LHC) at CERN. Within the Standard Model, the Wtb vertex is purely left-handed, and its amplitude is given by the Cabibbo-Kobayashi-Maskawa matrix element Vtb, related to weak interaction between a top and a b-quark. In a more general way, additional anomalous couplings such as right-handed vectorial couplings and left and right-handed tensorial couplings can also be considered. The study of the angular distribution of the top quark decay products at the LHC will allow precision measurements of the structure of the Wtb vertex, providing also an important probe for possible physics beyond the SM. In the present thesis, the ATLAS sensitivity to anomalous Wtb couplings is studied. For this, the t anti-t pair production at the LHC is considered and different observables, such as angular asymmetries and W helicity fractions and ratios, are discussed. The expected results for luminosities of 10/fb and 1/fb are obtained through the combination of the most sensitive observables

The first shall be last: selection-driven minority becomes majority

Street demonstrations occur across the world. In Rio de Janeiro, June/July 2013, they reach beyond one million people. A wrathful reader of \textit{O Globo}, leading newspaper in the same city, published a letter \cite{OGlobo} where many social questions are stated and answered Yes or No. These million people of street demonstrations share opinion consensus about a similar set of social issues. But they did not reach this consensus within such a huge numbered meetings. Earlier, they have met in diverse small groups where some of them could be convinced to change mind by other few fellows. Suddenly, a macroscopic consensus emerges. Many other big manifestations are widespread all over the world in recent times, and are supposed to remain in the future. The interesting questions are: 1) How a binary-option opinion distributed among some population evolves in time, through local changes occurred within small-group meetings? and 2) Is there some natural selection rule acting upon? Here, we address these questions through an agent-based model.Comment: 8 pages, 4 figures, accepted for publication in Physica

Loom: Unifying Client-Side Web Technologies in a Single Programming Language

Modern client-centred web applications typically depend on a set of complementary languages to control different layers of abstraction in their interfaces: the behaviour, structure, and presentation layers (in order, traditionally: JavaScript, HTML, and CSS). Applications with dynamic interfaces whose structure and presentation depend on the data and state of the application require tight links between such layers; however, communicating between them is often non-trivial or simply cumbersome, mainly because they are effectively distinct languages—each with a specific way of being interacted with. Numerous technologies have been introduced in an attempt to simplify the interaction between the multiple layers; their main focus so far, however, regards the communication between structure and behaviour—leaving room for improvement in the field of presentation. This dissertation presents Loom: a novel reactive programming language that unifies the enunciated abstraction layers of a client-side web application. Loom allows the specification of an interface’s structure and presentation in a declarative, data-dependent, and reactive manner by means of signals—values that change over time—inspired by the field of functional reactive programming: reactive meaning that when the structure and presentation of an interface depend on application-data, changes to said data cause an automatic update of the application’s interface. We provide an implementation of the language’s compiler that allows the creation of interfaces with performance comparable to that of most existent frameworks

BV and non-BV associated Gardnerella vaginalis establish similar synergistic interactions with other BV-associated microorganisms in dual-species biofilms

Dual-species biofilm formation between Gardnerella vaginalis strains isolated from women with or without bacterial vaginosis (BV) and other 24 BV-associated microorganisms support that the key difference in virulence potential between BV-negative and BV-positive G. vaginalis strains seems not to be related with biofilm maturation.FCT Strategic Project of UID/BIO/04469/2013 unit and the project RECI/BBB-EBI/0179/2012 (FCOMP-01-0124-FEDER-027462

Consumer engagement with football brands on Facebook

The growth of social media has forced brands to adapt the scope of their activities in terms of brand management, consumer engagement and customer communications. Football brands have recently started to understand the relevance of social media as a tool for exploiting the enormous potential they possess, much due to their well-established brand awareness, brand identity and, most of all, the passion they more easily trigger in fans. The goal of this research is to determine the most influential motivations that trigger consumers to engage with a football brand on Facebook. Furthermore, we want to understand if between brand love, brand image and consumer engagement influence brand loyalty towards football brands. To do so, we have collected data from 214 respondents that were questioned about this subject, after which we performed correlation analysis in order to test these relations. Our findings point out that entertainment, personal identity and social influence are the most influential types of motivations to engage with a football brand on Facebook. Trust in the brand, despite not showing the same relevance, also came out as a significant variable. Other results indicate that there is a positive relation between brand love, brand image, consumer engagement and, lastly, brand loyalty. Our findings and the respective managerial implications they might present are discussed, also providing indications and suggestions regarding future researches concerning this subject

Search for flavour changing neutral currents in top quark decays in ATLAS

[Excerpt] Within the Standard Model flavour changing neutral currents (FCNC) are forbidden at tree level and much smaller than the dominant decay mode (t → bW) at one loop level. Nonetheless, several Standard Model extensions predict higher branching fractions (BR) for the top quark FCNC decays [1], making the search for FCNC processes an important probe for new physics in the top quark sector. In the present analysis [2], the t → qZ decay channel is searched for by looking for top quark pair production with one top quark decaying through FCNC (t → qZ) and the other through the Standard Model dominant mode (t → bW). Only the leptonic decays of the Z and W bosons were considered (Z → e+e−,µ+µ− and W → eν,µν) as signal. ATLAS data collected at a centre-of-mass energy of √s = 7 TeV during 2010 and corresponding to an integrated luminosity of 35 pb−1 are used. Presently, the most stringent experimental limits on BR(t → qZ) were obtained by the DO Collaboration: BR(t → qZ) < 3.2% at 95% confidence level (CL) [3]. [...](undefined)info:eu-repo/semantics/publishedVersio

Extending the BiYacc framework with ambiguous grammars

Dissertação de mestrado em Computer ScienceContrarily to most conventional programming languages where certain symbols are used so as to create non-ambiguous grammars, most recent programming languages allow ambiguity. This results in the necessity for a generic parser that can deal with this ambiguity without loss of performance. Currently, there is a GLR parser generator written in Haskell, integrated in the BiYacc system, developed by Departamento de Informática (DI), Universidade do Minho (UM), Portugal in collaboration with the National Institute of Informatics, Japan. In this thesis, this necessity for a generic parser is attacked by developing disambiguation filters for this system which improve its performance, as well as by implementing various known optimizations to this parser generator. Finally, performance tests are used to measure the results of the developed work.Contrariamente às linguagens de programação mais convencionais em que certos símbolos eram utilizados por forma a criar gramáticas não ambíguas, as linguagens mais recentes permitem ambiguidade, que por sua vez cria a necessidade de um parser genérico que consiga lidar com esta ambiguidade sem grandes perdas de performance. Atualmente, existe um gerador de parsers GLR em Haskell integrado no sistema BiYacc, desenvolvido pelo DI, UM, Portugal, em colaboração com o National Institute of Informatics, Japão. Nesta tese, são desenvolvidos filtros de desambiguidade para este sistema que aumentam a sua performance, assim como são feitas otimizações a vários níveis e se implementa um gerador de parsers usando um algoritmo GLL, que poderá trazer várias vantagens a nível de performance comparativamente com o algoritmo GLR atualmente implementado. Finalmente, são feitos testes de performance para avaliar os resultados do trabalho desenvolvido