1,720,957 research outputs found
Exact Correlators from Conformal Ward Identities in Momentum Space and Perturbative Realizations
Full text linkThe general solution of the conformal Ward identities (CWI's) in momentum
space, and their matching to perturbation theory, allows to uncover some
specific characteristics of the breaking of conformal symmetry, induced by the
anomaly. It allows to compare perturbative features of the 1-particle
irreducible (1PI, nonlocal) anomaly action with the prediction of a similar
(but exact) nonlocal action identified by the CWI's. The two predictions can be
exactly matched at the level of 3-point functions. The analysis of the
and shows that both approaches - based either on 1PI or on the exact
solutions of the CWI's - predict massless (dynamical) scalar exchanges in
3-point functions as the signature of the conformal anomaly. In a local
formulation such 1PI actions exhibit a ghost in the spectrum which may induce
ghost condensation. We also discuss alternative approaches, which take to
Wess-Zumino forms of the action with an asymptotic dilaton, which should be
considered phenomenological alternatives to the exact nonlocal action. If
derived by a Weyl gauging, they also include a ghost in the spectrum. The two
formulations, nonlocal and of WZ type, can be unified under the assumption that
they describe the same anomaly phenomenon at two separate (UV/IR) ends of the
renormalization group flow, possibly separated by a vacuum rearrangement at an
intermediate scale. A similar analysis is presented for an
supersymmetric Yang-Mills theory. We comment on the possibile cosmological
implications of such quasi Nambu-Goldstone modes as ultralight dilatons and
axions
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
Συσχετιστές τεσσάρων σημείων τανυστών τάσης σε χώρο κυματικού αριθμού και τοπολογικοί όροι στη βαρύτητα
No full textΙn the first part, we concentrate on CFTs in coordinate space. We lay the foundations of Conformal Field Theory and we also demonstrate a method where by using the embedding formalism we can derive up to n-point scalar conformal correlators. We proceed with our analysis in momentum space and we illustrate the theory of the conformal anomalies. We move on to analyse the renormalization of the correlators through counterterms followed by a discussion of the anomaly action. In the second part of the thesis. we derive and analyze the conformal Ward identities (CWIs) of a tensorial 4-point function of a generic CFT in momentum space. The correlator involves the stress-energy tensor T and three scalar operators O ().We derive the structure of the corresponding CWIs in two different sets of variables, relevant for the analysis of the 1-to-3 (1 graviton → 3 scalars) and 2-to-2 (graviton + scalar → two scalars) scattering processes. Then, we move on to another conformal correlator, the one made of four stress-energy tensors. We elaborate on the structure of the conformal anomaly effective action up to 4-th order, in an expansion in the gravitational fluctuations (h) of the background metric, in the flat spacetime limit. We discuss the renormalization of 4-point functions containing insertions of stress-energy tensors (4T), in conformal field theories in four spacetime dimensions. Finally, we include an analysis on the topological terms that are involved in the renormalization and consequently corrections of gravitational theories.Στο πρώτο μέρος της διατριβής επικεντρωνόμαστε στις Σύμμορφες Θεωρίες Πεδίου (CFTs) στο χώρο των θέσεων. Αφού θέσουμε τα θεμέλια των Σύμμορφων Θεωριών Πεδίου, αναδεικνύουμε μια μέθοδο που, με χρήση του embedding space φορμαλισμού, μπορούμε να παράγουμε τις βαθμωτές συναρτήσεις συσχετισμού n-σημείων. Στη συνέχεια της ανάλυσής μας, συζητάμε σύμμορφες ανωμαλίες στο χώρο των ορμών και την επανακανονικοποίηση των συναρτήσεων συσχετισμών με χρήση αντισταθμιστικών όρων ώστε να καταλήξουμε στη θεωρία της ανώμαλης δράσης. Στο δεύτερο μέρος, εξάγουμε και αναλύουμε τις σύμμορφες ταυτότητες του Ward (Conformal Ward Identities - CWIs) συναρτήσεων 4 σημείων με τανυστές τάσης.Οι συναρτήσεις αυτές περιλαμβάνουν τον τανυστή τάσης ενέργειας Τ και 3 βαθμωτούς τελεστές Ο ( TOOO ). Εξάγουμε τη δομή των CWIs σε δύο διαφορετικές διατάξεις των μεταβλητών, που σχετίζονται είτε με τις διαδικασίες σκέδασης, 1 σε 3 (1 γκραβιτόνιο → 3 βαθμωτά πεδία) είτε με τη διαδικασία 2 σε 2 (γκραβιτόνιο + βαθμωτό → 2 βαθμωτά). Συνεχίζουμε την ανάλυσή μας με βάση μια διαφορετική συνάρτηση συσχετισμού, εκείνη με 4 τανυστές τάσης. Μελετάμε τη δομή της σύμμορφης "ενεργής" και ανώμαλης δράσης μέχρι την 4η τάξη σε μια επέκταση με βάση τις βαρυτικές διακυμάνσεις (h) της μετρικής υποβάθρου στο όριο του επίπεδου χωροχρόνου. Σχολιάζουμε την επανακανονικοποίηση των συναρτήσεων 4 σημείων με τανυστές τάσης (4Τ) στις Σύμμορφες Θεωρίες Πεδίου σε τέσσερις διαστάσεις. Καταλήγουμε με μια ανάλυση των τοπολογικών όρων που εμπλέκονται στην επανακανονικοποίηση και συνεπώς στις διορθώσεις βαρυτικών θεωριών
Το μοντέλο Sachdev-Ye-Kitaev
Full text linkΕθνικό Μετσόβιο Πολυτεχνείο--Μεταπτυχιακή Εργασία. Διεπιστημονικό-Διατμηματικό Πρόγραμμα Μεταπτυχιακών Σπουδών (Δ.Π.Μ.Σ.) “Φυσική και Τεχνολογικές Εφαρμογές
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
- …
