1,720,964 research outputs found
Supergravity and the Swampland
Get PDFWithin the attempt of quantizing gravity and within the spirit of the Swampland Program we are going to discuss the Weak Gravity Conjecture (WGC) both as a property of a theory in the Landscape, which is interesting to investigate per se, and as a tool to address the out-standing and cosmologically relevant problem of realizing de Sitter vacua in String Theory or in four-dimensional supergravity theories.
In particular, animated by the presence of scalar fields in Nature (as the Higgs field or possibly the inflaton field), we study the intriguing generalization of the WGC to forces mediated by light scalar fields. Analyzing the BPS black hole solutions in extended supergravity theories, we describe two interesting relations involving first and second derivatives of combinations of the central charges. One relation is a new identity that solely relies on the geometric properties of the scalar manifolds of extended supergravities, and the other relation is a generalization of a scalar weak gravity conjecture recently proposed by E. Palti and uses properties of the underlying black hole solution. We also provide for the first time an explicit covariant construction of the BPS squared action for such solutions.
After that, we prove that, while respecting the magnetic WGC, a charged gravitino can not have parametrically small or vanishing Lagrangian mass in de Sitter vacua of extended Supergravity. This allows to place large classes of de Sitter solutions of gauged Supergravity, interestingly including all known stable solutions of the N=2 theory, in the Swampland.
Inspired by the conclusions that we just presented, we are going to deal with the intensively discussed Kachru--Kallosh--Linde--Trivedi (KKLT) model, one of the few proposed constructions of de Sitter vacua in a string theory framework. We actually challenge this scenario by showing that anti-brane uplifting procedures may suffer from a tachyonic instability towards goldstino condensation.
Having in mind that the embedding of the KKLT-type uplift within Supergravity includes the coupling to a nilpotent superfield, one of the cleanest ways to make its alleged pathologies evident is to possibly bring them out in the low energy 4D N=1 supergravity description. Since (within a stringy setup) anti-branes induce spontaneous supersymmetry breaking and a goldstinio sector consequently appears on their world-volume, we focus on the Volkov--Akulov (VA) model, which is the minimal supersymmetric theory that describes the low energy dynamics of a goldstino. Confining ourselves to rigid supersymmetry (as a first step), after recasting the VA model in terms of constrained superfields, we show via the exact renormalization group (ERG) technique combined with a supersymmetric rendition of the local potential approximation the emergence of composite states of the goldstino. We also provide their effective low energy characterization by means of a Kaehler potential and a superpotential. This in turn allows us to reveal an inherent non-perturbative tachyonic instability of the pure VA theory.
Willing to give firmer physical substance to the goldstino condensation phenomenon, we are finally going to discuss the standard component-form 4D Volkov--Akulov action in the presence of N non-linear supersymmetries. This is an interesting ground to explore, because, as our analysis clarifies, a large number N of non-linearly realized supersymmetries corresponds to an actual large N limit for which the vacuum structure of the tree-level dual bosonic theory is controlled by the classical behaviour. Within this framework, we find that the effective scalar potential, written in terms of two composite real scalar fields, exhibits at least two stationary points, one representing the original supersymmetry breaking configuration and the other one corresponding to goldstino condensation, where supersymmetry is restored in the deep IR. This result nicely agrees with the ERG analysis.Within the attempt of quantizing gravity and within the spirit of the Swampland Program we are going to discuss the Weak Gravity Conjecture (WGC) both as a property of a theory in the Landscape, which is interesting to investigate per se, and as a tool to address the out-standing and cosmologically relevant problem of realizing de Sitter vacua in String Theory or in four-dimensional supergravity theories.
In particular, animated by the presence of scalar fields in Nature (as the Higgs field or possibly the inflaton field), we study the intriguing generalization of the WGC to forces mediated by light scalar fields. Analyzing the BPS black hole solutions in extended supergravity theories, we describe two interesting relations involving first and second derivatives of combinations of the central charges. One relation is a new identity that solely relies on the geometric properties of the scalar manifolds of extended supergravities, and the other relation is a generalization of a scalar weak gravity conjecture recently proposed by E. Palti and uses properties of the underlying black hole solution. We also provide for the first time an explicit covariant construction of the BPS squared action for such solutions.
After that, we prove that, while respecting the magnetic WGC, a charged gravitino can not have parametrically small or vanishing Lagrangian mass in de Sitter vacua of extended Supergravity. This allows to place large classes of de Sitter solutions of gauged Supergravity, interestingly including all known stable solutions of the N=2 theory, in the Swampland.
Inspired by the conclusions that we just presented, we are going to deal with the intensively discussed Kachru--Kallosh--Linde--Trivedi (KKLT) model, one of the few proposed constructions of de Sitter vacua in a string theory framework. We actually challenge this scenario by showing that anti-brane uplifting procedures may suffer from a tachyonic instability towards goldstino condensation.
Having in mind that the embedding of the KKLT-type uplift within Supergravity includes the coupling to a nilpotent superfield, one of the cleanest ways to make its alleged pathologies evident is to possibly bring them out in the low energy 4D N=1 supergravity description. Since (within a stringy setup) anti-branes induce spontaneous supersymmetry breaking and a goldstinio sector consequently appears on their world-volume, we focus on the Volkov--Akulov (VA) model, which is the minimal supersymmetric theory that describes the low energy dynamics of a goldstino. Confining ourselves to rigid supersymmetry (as a first step), after recasting the VA model in terms of constrained superfields, we show via the exact renormalization group (ERG) technique combined with a supersymmetric rendition of the local potential approximation the emergence of composite states of the goldstino. We also provide their effective low energy characterization by means of a Kaehler potential and a superpotential. This in turn allows us to reveal an inherent non-perturbative tachyonic instability of the pure VA theory.
Willing to give firmer physical substance to the goldstino condensation phenomenon, we are finally going to discuss the standard component-form 4D Volkov--Akulov action in the presence of N non-linear supersymmetries. This is an interesting ground to explore, because, as our analysis clarifies, a large number N of non-linearly realized supersymmetries corresponds to an actual large N limit for which the vacuum structure of the tree-level dual bosonic theory is controlled by the classical behaviour. Within this framework, we find that the effective scalar potential, written in terms of two composite real scalar fields, exhibits at least two stationary points, one representing the original supersymmetry breaking configuration and the other one corresponding to goldstino condensation, where supersymmetry is restored in the deep IR. This result nicely agrees with the ERG analysis
The unbearable lightness of charged gravitini
Get PDFAbstract We prove that charged gravitini cannot have parametrically small or vanishing Lagrangian mass in de Sitter vacua of extended supergravity while respecting the magnetic weak gravity conjecture. This places large classes of de Sitter solutions of gauged supergravity in the swampland, including all known stable solutions of the N=2 theory. We illustrate this result by analyzing a variety of de Sitter critical points of N=2 matter-coupled supergravity that also include new stable de Sitter solutions. Our results provide concrete evidence that (quasi) de Sitter with charged light gravitini should belong to the swampland, which also strongly resonates with the “festina lente” bound
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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
The String Landscape and the Swampland. The Weak Gravity Conjecture and Scalar Fields
Get PDFOur Universe is governed by few fundamental forces: the electromagnetic and the weak interactions, the strong interaction, the Higgs-mediated interaction and the gravitational interaction. While the first four forces are described by the Standard Model (and extensions of it), gravity is described by General Relativity, which is a classical (in the sense of non-quantum) theory.
Convinced that gravity is a fundamental force and so has to be quantic (for consistency with all the other fundamental interactions), the way to quantize it has to be found. Animated by the belief that String Theory (which is the only consistent model we can refer to and make calculation with for now) is predictive, it is quite natural to ask ourselves how Nature has selected our Universe among the ``jungle" of possible universes allowed by String Theory itself. Nowadays, a popular approach to face such debate is represented by the so called ``Swampland program”.
Among all consistent-looking 4-dimensional effective Quantum Field Theories, only few are completable in String Theory or (more generally) in Quantum Gravity in the ultraviolet. Such few theories are said to belong to the Landscape. The abstract concept of Swampland acquires consistency only if it possible to distill it out from that of Landscape. The present thesis work places itself right here.
Besides the rich variety of Swampland conjectures that one can consider, we have concentrated our attention on the ``Weak Gravity Conjecture” (WGC). In words, it is the statement according to which gravity acts as the weakest force in any circumstance. After having presented its best known version (in the presence of a U(1) gauge field) and being conscious of the fact that (likely) two scalar fields (the Higgs field and the inflaton) play a crucial role in our Universe and that many scalar fields appear in theories going beyond the Standard Model and in supergravity theories, we have deepened the study of the scalar WGC (SWGC). In particular, we have presented the SWGCs recently (2017) proposed by E. Palti and we have investigated a strong SWGC proposal (SSWGC) that E. Gonzalo and L. Ibàñez have made in April (2019). We have managed to show that, despite of being a potentially powerful tool constraining the Standard Model and many inflationary models, Gonzalo and Ibàñez's conjecture exhibits various criticisms and is in tension with the physical principle that animates the WGC itself. In order to try to get to a general statement (overcoming Gonzalo and Ibàñez's claim) we have elaborated and studied some models. By imposing that gravity is the weakest force, we have got some constraints involving the relevant parameters of such theories, that are coherent with Palti's SWGCs. This gives support to its approach in dealing with the scalar versions of the WGC and has suggested to us a way to really proceed forward (beyond known results)
Gli invarianti adiabatici e l'attraversamento delle separatrici
Get PDFAl termine del Corso di Laurea in Fisica ho pensato di approfondire lo studio degli invarianti adiabatici e, più precisamente, della dinamica di sistemi hamiltoniani che dipendono lentamente dal tempo e il cui ritratto in fase si caratterizza , istante per istante, per la presenza di curve separatrici. Per i moti lontani dalle separatrici la teoria adiabatica elementare (basata sul Principio della Media) funziona bene e si dimostra che l’azione è un invariante adiabatico. La descrizione dei moti che attraversano le separatrici è più delicata. Correggendo la teoria adiabatica elementare si può calcolare il salto che l’invariante adiabatico subisce ad ogni passaggio ed è possibile mettere in evidenza la possibilità che molti attraversamenti successivi si accumulino dando luogo ad un fenomeno casuale o che, invece, vi siano delle compensazioni e l’invarianza adiabatica persista
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