1,721,021 research outputs found
A systematic study of phenomenological implications of dim-6 operators
Full text linkThe Standard Model (SM) of particle physics has been producing reliable estimates to a high precision level in the last few decades. Moreover, the discovery of a scalar particle with properties consistent with the SM Higgs boson, together with the fact that no Beyond Standard Model (BSM) particle has been detected so far, suggests that the New Physics (NP) scale Lambda can be placed above the electro-weak symmetry breaking (EWSB) scale.
Therefore, an effective field theory built solely using the SM fields, called Standard Model Effective Field Theory (SMEFT), can be used to describe the low energy limit of BSM physics. This theory should be written adding to the renormalizable SM interactions further terms of higher dimensions, suppressed by suitable powers of the scale Lambda and invariant under the SM gauge group. The schematic Lagrangian is
L_SMEFT = LSM + L_5 + L_6 + ...
L_5 contains only the Weinberg operator, which can be used to provide masses to neutrinos. Assuming the conservation of baryon number, in L_6 there are 59 operators, many of which have flavour indices (explicitly taking them into account, the number of operators grows up to 2499). The full one-loop anomalous dimension (AD) matrix needed for renormalization group evolution (RGE) of the dimension 6 operators has been recently computed; several entries have been found to be of order 1, therefore suggesting a relevant mixing between some of these operators.
The SMEFT approach can be used to interpret several patterns of deviations in SM processes: it allows for model independent analysis, which is a particularly useful feature given our present lack of knowledge regarding the ultraviolet (UV) completion of the SM theory. The BSM fields can in fact be integrated out of the theory at the NP scale, in such a way that there is no evident sign of their presence at the EWSB scale, but their effects can be mimicked by means of the couplings of the higher dimension operators; it will therefore be possible to use experimental informations in order to constrain the bounds of the such couplings, which can be consequently reinterpreted as bounds on the NP scale once the SMEFT is mapped on the desired UV completion of the theory.
In my PhD project, I have focused my attention to phenomenological implications due to the effect of dimension 6 operators. As a first step of my project, I have partially recomputing the AD, in order to check the correctness of their results.
Subsequently, I have been involved in analyses concerning the status of the anomalies present in B physics, with a particular focus on b to s transitions. My work on the field, aiming at discerning the shape of the potential NP underling such processes and potentially disentangling it from effects stemming from QCD effects, is reported in Refs.~\cite{Ciuchini:2015qxb,Ciuchini:2016weo,Ciuchini:2017gva,Ciuchini:2017mik}. A systematic reinterpretation of such findings in the SMEFT framework is an original contribution to this PhD thesis, and is yet to be published. Moreover, I have spent some time working on the study of the trilinear Higgs self-coupling. Given the large room for NP effects to such coupling, induced by the present status of the experimental constraints, the (SM)EFT approach is not a phenomenologically-meaningful framework to employ in order to study potential BSM effects in this sector. Therefore, I have adopted an alternative method to approach the matter, exploiting the study of electroweak precision observables in order to further constrain the bound that can be put on the Higgs trilinear self-coupling~\cite{Degrassi:2017ucl}
Perturbative corrections in the Standard Model
No full textIn questa tesi di dottorato studiamo l'impiego di alcune recenti tecniche per calcolare correzioni radiative nel contesto del Modello Standard. In particolare, ci concentriamo sugli integrali di loop (Integrali di Feynman) che intervengono nelle correzioni radiative agli osservabili del Modello Standard. Il calcolo esplicito degli integrali di Feynman è in genere molto complicato e il loro calcolo può essere fatto risolvendo equazioni differenziali piuttosto che integrare direttamente gli integrali di Feynman. Si può dimostrare che utilizzando alcune particolari identità il numero molto grande di integrali di Feynman da calcolare esplicitamente può essere ridotto a un numero molto più piccolo di integrali, chiamati "Master Integrals". I master integrals in particolare soddisfano un sistema di equazioni differenziali del primo ordine nelle variabili cinematiche. La risoluzione di questo sistema di equazioni applicato ad alcuni processi fisici cruciali nella fisica delle particelle è l'oggetto di questa tesi. Per essere più specifici, ci occupiamo dei seguenti processi: 1. correzioni elettrodeboli planari alla produzione di un bosone di Higgs in aggiunta a un jet adronico nel canale di fusione di gluoni. 2. correzioni di QCD non-planari alla produzione di una coppia di quark top-antitop nel canale di quark antiquark legger
Corte costituzionale e autonomie speciali in materia di aree protette
No full textIl saggio analizza il riparto di competenze tra Stato e Regioni e le politiche in materia di aree protette, con particolare riguardo alla giurisprudenza della Corte costituzionale
Two-loop electroweak corrections to Higgs production in proton-proton collisions
No full textWe study the impact of the two-loop electroweak corrections on the production of a Higgs boson via gluon-fusion in proton-proton collisions at LHC energies. We discuss the prescritpion to include the corrections to the hard scattering matrix element in the calculation of the hadronic cross-section sigma (p+p\to H+X). Under the hypothesis of factorization of the electroweak corrections with respect to the dominant soft and collinear QCD radiation, we observe an increase of the total cross-section from 4 to 8 %, for MH <=160 GeV. This increase is comparable with the present QCD uncertainties originating from hard scattering matrix elements
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
- …
