1,720,959 research outputs found
A large- tensor model with four supercharges
Full text linkWe study a supersymmetric tensor model with four supercharges and
global symmetry. The model is based on a chiral scalar superfield with three
indices and quartic tetrahedral interaction in the superpotential, which is
relevant below three dimensions. In the large- limit the model is dominated
by melonic diagrams. We solve the Dyson-Schwinger equations in superspace for
generic and extract the dimension of the chiral field and the dimensions of
bilinear operators transforming in various representations of . We find
that all operator dimensions are real and above the unitarity bound for
. Our results also agree with perturbative results in
expansion. Finally, we extract the large spin behaviour of bilinear operators
and discuss the connection with lightcone bootstrap.Comment: 29 pages, 10 figure
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
Non-perturbative aspects of Quantum Field Theory
Full text linkThe main focus of this thesis is Quantum Field Theory and our investigation goes in two main directions. In a the first part (chapters 3 and 4) we mainly use the large-N expansion as a tool to investigate some non-perturbative properties of O(N) vector models and O(N)^3 tensor models. Also (chapter 5), we study the critical properties of cubic and quartic fractional Lifshitz field theory using standard perturbation theory. In the second part (chapter 6) we study again the O(N) vector model, but this time as a zero dimensional toy model of a QFT, on which we develop constructive techniques and describe non-perturbative contributions coming from instantons.
Chapters 1 and 2 are an introduction to the original research results, where we explain the context in which our work needs to be framed and give an overview of the most important technical tools that we used.
In chapter 3 we study a long-range tensor model with O(N)^3 symmetry, which was proven to have four lines of fixed points in the large-N limit. In particular, we test the famous F-theorem on such model, stating that in d = 3 the free energy on the sphere is monotonically decreasing going from the ultraviolet to the infrared along the renormalization group flow. We compute explicitly the free energy at two fixed points connected by a renormalization group trajectory and find that the F-theorem holds, which can be thought of as a further hint for the unitarity of the theory. The computation was technically challenging and it required to sum and infinite family of diagrams by means of the Conformal Partial Waves expansion. Also, we review the O(N) vector model at large-N, that we use as a warm-up exercise to test our technology.
In chapter 4 we investigate the effects of compatifying one direction on Conformal Field Theories. The compact direction necessarily introduces an energy scale, i.e. the inverse of its size, that breaks conformal invariance. The main consequence is that one-point functions are no more constrained to be zero, enlarging the set of CFT data needed to fully characterize the theory. We review the long-range O(N) vector model with one compact direction, show the existence of a non-trivial solution of the mass gap equation and of a stable IR fixed point at large-N. We compute the one-point functions of a specific family of bilinear operators at the large-N fixed point. Furthermore, we stress and discuss the difference between a classical statistical field theory and its corresponding quantum version, which becomes manifest when dealing with long-range theories. Indeed, long-range interactions are described by an action with a fractional Laplacian in the space directions, while the usual term with the double derivative with respect to time, coming from the quantum-to-classical mapping, is unchanged. Such kind of theories, which we call quantum fractional Lifshitz field theories, are manifestly anisotropic and the different role of time and space is evident, as opposed to the more common short-range theories in which their difference might be overlooked when working in Euclidean signature.
In chapter 5 we investigate the critical properties of quantum fractional Lifshitz field theories with cubic and quartic interaction. One interesting feature of Lifshitz field theories is that, while they break explicitly Lorentz or rotation invariance, they exhibit anisotropic scale invariance at fixed points of the renormalization group. Such anisotropic scale invariance is fully described by the anisotropy exponent z, which we compute to the first non-trivial order in perturbation theory.
In chapter 6 we study the quartic O(N) vector model in zero dimensions, i.e. as a purely combi- natorial toy model of a QFT. Working in zero dimensions fully trivialize the problem of computing Feynman amplitudes, making us able to study more easily the properties of the asymptotic perturba- tive expansion. We study both the partition function and the free energy as functions of the coupling constant by using constructive techniques such as the BKAR formula and Loop Vertex Expansion. The Loop Vertex Expansion requires to introduce an Hubbard–Stratonovich auxiliary field and it has the remarkable feature of having a finite radius of convergence. Furthermore, in the case of the O(N) model, it formally corresponds to a small-N expansion. We prove Borel summability of both the partition function, the free energy and the coefficients of their small-N expansion in all the direc- tions of the complex plain. In order to do this, we need to analytically continue such quantities on a multi-sheeted Riemann surface, i.e. past a Stokes line. Finally, we compute their full transseries expansion which, past the Stokes lines, includes instanton-like non-analytic contribution encoding all the non-perturbative information. Despite the fact that some of the results on the topic were already understood by other means, we believe that our work is relevant as it set the ground for repeating the same analysis in QFT
Melonic Dominance in Tensor Field Theories
No full textLa tesi si propone di studiare delle particolari teorie quantistiche di campo i cui campi fondamentali sono tensori di rango 3. Nel limite di grande numero componenti, solo una piccola parte dei diagrammi contribuisce alle funzioni di correlazione ed è possibile risommarli esattamente imponendo relazioni di autoconsistenza. Il punto d'arrivo consiste nello studiare con questo approccio un modello supersimmetrico con 4 supercariche, i cui campi fondamentali sono chirali e anti-chirali. Grazie al troncamento dei diagrammi e ai vincoli imposti dalla supersimmetria, vengono calcolate la dimensione anomala dei campi e lo spettro degli operatori bilineari scalari al punto fisso infrarosso. I risultati ottenuti vengono poi messi a confronto con quelli già calcolati in letteratura con metodi perturbativi ed appaiono in perfetto accordo.
The thesis proposes to study particular quantum field theories whose fundamental fields are tensors of rank 3. In the limit of large number of components, only a small part of the diagrams contributes to the correlation functions and it is possible to sum them exactly by imposing self-consistency relations. The point of arrival consists in studying with this approach a supersymmetric model with 4 supercharges, whose fundamental fields are chiral and anti-chiral. Thanks to the truncation of the diagrams and the constraints imposed by the supersymmetry, the anomalous dimension of the fields and the spectrum of the bilinear scalar operators at the infrared fixed point are calculated. The results obtained are then compared with those already calculated in the literature with perturbative methods and appear in perfect agreement
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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