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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
691

Cordas em espaços deformados / Strings in deformed space

Sergio Augusto Jardino Filho 19 March 2009 (has links)
Nesta tese foram estudadas configurações de cordas em movimentos de rotação e de oscilação no âmbito da correspondência AdS/CFT. Estas cordas movimentam-se nos espaços AdS5 × S5, de Lunin e Maldacena, R1, 9 e R1, 9 deformado. Para o caso da corda em rotação, determinou-se a existência do mágnon gigante e da corda farpada. Para o caso da corda oscilante, foram encontradas as soluções das equações de movimento clássicas e determinada a energia. Também calculamos explicitamente o número de supercargas preservadas para os espaços AdS5 × S5 e para R1, 9 deformado. / In this thesis we studied rotating and oscillating strings under the AdS/CFT correspondence. These strings move in the AdS5 × S5, Lunin and Maldacena, R1, 9 and deformed R1, 9 spaces. In the case of the rotating string, the giant magnon and the spiky string were determined. In the case of the oscillating string, we found the solutions fo the classical equations of motion and the energy. We also explicitly calculated the number of preserved supercharges for the AdS5 × S5and deformed R1, 9 spaces.
692

O modelo de Landau-Lifshitz e a integrabilidade em teoria de cordas / The Landau-Lifshitz model and the integrability in string theory

Gabriel Weber Martins 17 November 2011 (has links)
Nesta tese, estudamos a integrabilidade quântica de modelos contínuos relevantes no contexto da quantização da supercorda do tipo IIB em AdS5 x S5, e, conseqüentemente, de interesse para a demonstração e uma melhor compreensão da correspondência AdS/CFT. Para os modelos de Landau-Lifshitz e de Alday-Arutyunov-Frolov, calculamos as amplitudes de espalhamento para três partículas e mostramos a fatorabilidade de suas matrizes S em primeira ordem não-trivial. Propomos também um novo método para a quantização de sistemas integráveis contínuos no exemplo do modelo de Landau-Lifshitz su(1;1). Nosso método fornece uma solução alternativa para o problema do ordenamento operatorial, bem como uma prescrição para a dedução das identidades de traço e do espectro das cargas quânticas conservadas. Ademais, mostramos que, por ser baseado em um processo de regularização e renormalização operatorial, concomitante à construção das extensões auto-adjuntas, a integrabilidade é preservada durante a quantização. / In this thesis, we study the quantum integrability of continuous models which arise from consistent truncations of type IIB superstring theory on AdS5 X S5, and, therefore are relevant for improving our current understanding of the AdS/CFT correspondence. For the Landau-Lifshitz and the Alday-Arutyunov-Frolov models, we compute the three-particle scattering amplitude and show the factorizability of the corresponding S matrices at the first non-trivial order. We also propose a new method for quantizing continuous integrable systems and apply it to the su(1;1) Landau-Lifshitz model. Our method provides an alternative solution to the longstanding operator ordering problem and gives a prescription to obtain the quantum trace identities, and the spectrum for the higher-order local charges. Moreover, since it is based on operator regularization and renormalization, as well as on the construction of the self-adjoint extensions, the integrability is preserved during the quantization process
693

Propriedades tecnológicas, nutricionais e sensoriais de biscoito tipo cookie sem glúten, desenvolvido com arroz de diferentes teores de amilose e feijãocaup / Technological, nutritional and sensory properties of gluten-free cookies, deeloped with rice exhibiting different amylose contents and cowpea

Souza, Estefania Julia Dierings 14 June 2018 (has links)
Submitted by Gabriela Lopes (gmachadolopesufpel@gmail.com) on 2018-07-27T18:52:58Z No. of bitstreams: 1 DISSERTAÇÃO ESTEFANIA_JULIA_DIERINGS_SOUZA_FINAL.pdf: 1787909 bytes, checksum: 80c02458a0ad77d346a0b43ad9d441e1 (MD5) / Approved for entry into archive by Aline Batista (alinehb.ufpel@gmail.com) on 2018-07-31T18:55:04Z (GMT) No. of bitstreams: 1 DISSERTAÇÃO ESTEFANIA_JULIA_DIERINGS_SOUZA_FINAL.pdf: 1787909 bytes, checksum: 80c02458a0ad77d346a0b43ad9d441e1 (MD5) / Made available in DSpace on 2018-07-31T18:55:04Z (GMT). No. of bitstreams: 1 DISSERTAÇÃO ESTEFANIA_JULIA_DIERINGS_SOUZA_FINAL.pdf: 1787909 bytes, checksum: 80c02458a0ad77d346a0b43ad9d441e1 (MD5) Previous issue date: 2018-06-14 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / O uso de farinha de arroz é uma alternativa muito utilizada em produtos de panificação sem glúten, contudo a composição e características dos produtos depende das particularidades das farinhas utilizadas em sua elaboração. Objetivou-se com o estudo avaliar os efeitos de farinhas mistas de arroz, com diferentes teores de amilose, e feijão-caupi sobre propriedades tecnológicas, nutricionais e sensoriais de biscoitos tipo cookie. Para tanto, foram analisadas as propriedades das farinhas, como composição proximal, solubilidade e absorção de água, atividade de água, proteína solúvel e digestibilidade proteica. Os parâmetros de qualidade de biscoito tipo cookie como composição proximal, atividade de água, proteína solúvel, digestibilidade proteica, espessura, diâmetro, fator de dispersão, textura, cor, perfil de aminoácidos e análise sensorial com os testes de preferência, aceitação e intenção de compra foram avaliados. Os biscoitos tipo cookies preparados com a formulação contendo farinha de arroz de alto (BRS Catiana) e médio teor de amilose (EEA 406) apresentaram, respectivamente os menores valores de dureza enquanto que os elaborados com farinhas de arroz baixo teor de amilose (Cateto) apresentaram maior fraturabilidade. Os biscoitos tipo cookies elaborados com farinha de arroz de baixo teor de amilose (cateto) apresentaram sensorialmente maior dureza e mais escuros. Os biscoitos tipo cookies elaborados com farinha de arroz de alto teor de amilose (BRS Catiana) apresentaram coloração mais clara, menor dureza e maior preferência. Os atributos odor e sabor não apresentam diferença entre as formulações. / The use of rice flour is a widely used alternative in gluten-free baking products, however the composition and characteristics of the products depends on the particularities of the flour used in its preparation. The objective of this study was to evaluate the effects of mixed rice flour with different levels of amylose and cowpea on technological, nutritional and sensory properties of cookie. The properties of flours, such as proximal composition, solubility and water absorption, water activity, soluble protein and protein digestibility were analyzed. Cookie quality parameters such as proximal composition, water activity, soluble protein, protein digestibility, thickness, diameter, dispersion factor, texture, color, amino acid profile and sensory analysis with the tests of preference, acceptance and intention of were evaluated. Cookies prepared with the formulation containing high (BRS Catiana) and medium amylose (EEA 406) rice flour had the lowest values of hardness, respectively, while those made with low amylose (Cateto) rice flour, presented greater fracture. Cookies made with rice flour with low amylose content (Cateto) were sensorially harder and darker. Cookies made with high amylose (BRS Catiana) rice flour showed lighter color, less hardness and higher preference. The odor and taste attributes do not present differences between the formulations.
694

Uma orquestra de viola caipira do município de São Carlos / A brazilian ten-string guitar orchestra from the city of São Carlos

Pedro, Renato Cardinali, 1981- 23 August 2018 (has links)
Orientador: José Roberto Zan / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Artes / Made available in DSpace on 2018-08-23T23:24:52Z (GMT). No. of bitstreams: 2 Pedro_RenatoCardinali_M.pdf: 4003211 bytes, checksum: c177a9a4597ecda867aec690a1740dbf (MD5) Pedro_RenatoCardinali_Anexo.zip: 93548042 bytes, checksum: ed20c54416700bf4929a3073e2fb3a5b (MD5) Previous issue date: 2013 / Resumo: Este trabalho é resultado da pesquisa realizada sobre a Orquestra Amigos Violeiros de São Carlos, uma formação musical de caráter social sem fins lucrativos, que se dedica à prática da viola caipira. O enfoque principal foi investigar como o envolvimento com a Orquestra ativa aspectos de identificação destes sujeitos com a cultura caipira e a música sertaneja. Para tanto, utilizamos os métodos etnográficos e etnomusicológico que busca compreender os sentidos das ações dos sujeitos envolvidos nessa formação musical, suas representações e prática musical. Os procedimentos realizados para a coleta dos dados foram observações participantes dos ensaios e apresentações do grupo, registradas em caderno de campo, entrevistas e gravações de áudio e vídeo. Além disso, abordamos aspectos históricos da viola, da cultura caipira, do segmento musical sertanejo, bem como da formação e desenvolvimento da Orquestra. A partir das análises dos dados, foi identificado como o envolvimento dos integrantes com o grupo e com sua prática musical ativa aspectos de identificação destes sujeitos com o que consideram ser a cultura caipira / Abstract: This work is the result of the research conducted on the Orchestra Amigos Violeiros of São Carlos. A non-profit and social musical formation dedicated to the practice of Brazilian ten-string guitar. The main focus was to investigate how the involvement with the Orchestra activates identification aspects of these subjects with the caipira culture and Brazilian country music. Therefore, it was used ethnographic and ethnomusicological methods that seeks to understand the meanings behind the actions of those involved with the musical formation, its representations and musical practice. The procedures carried out for data collection were participant observation of rehearsals and performances of the group, recorded in the field notebook, interviews and audio and video recordings. Besides, it was discussed historical aspects of the viola, the caipira culture, the Brazilian country musical segment as well as the formation and development of the Orchestra. From the data analysis, it was identified how the involvement of the members in the group and their musical practice activates identification aspects of these subjects with what they consider to be the caipira culture / Mestrado / Fundamentos Teoricos / Mestre em Música
695

Entre o sertão e a sala de concerto : um estudo da obra de Renato Andrade / Between Brazilian inland and the concert room : a Renato Andrade's work study

Pereira, Vinícius Muniz 20 August 2018 (has links)
Orientador: José Roberto Zan / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Artes / Made available in DSpace on 2018-08-20T10:01:07Z (GMT). No. of bitstreams: 1 Pereira_ViniciusMuniz_M.pdf: 56101342 bytes, checksum: 514793000f3a81a61f247c0ccd82a831 (MD5) Previous issue date: 2011 / Resumo: Em meados da década de 1970, o compositor e instrumentista mineiro Renato Andrade lança seu primeiro disco solo intitulado A fantástica viola de Renato Andrade. No repertório, composições instrumentais interpretadas com muito virtuosismo na viola caipira. Esse é o início de uma produção precursora dentro da música sertaneja e que acabou por criar um novo segmento desse gênero. Resultado das transformações formais e estéticas da música popular brasileira a partir dos anos 70, a obra de Renato Andrade reflete o surgimento de fronteiras tênues entre a esfera popular e erudita, na qual compositores e instrumentistas vão buscar nas "tradições" populares elementos destinados a dar "autenticidade" e "legitimidade" às suas produções, ao mesmo tempo adotam procedimentos da música erudita para dar corpo e organicidade a suas músicas. Esta dissertação buscou investigar a obra do compositor e violeiro Renato Andrade. Para isso, partiu dos dados biográficos do artista, do levantamento de sua produção fonográfica e a partir desses dados procurou compreender as estratégias criativas de Renato Andrade, a maneira com qual o músico organiza o material musical na viola caipira e a consolidação daquilo que identificamos como sendo o seu idioma composicional. Num segundo momento, o foco deste trabalho foi compreender o performer Renato Andrade, sua atuação nos palcos e a construção do que identificamos como o personagem Renato Andrade / Abstract: In the 1970's, the composer and performer from Minas Gerais Renato Andrade releases his first record playing solo. It was called A fantástica viola de Renato Andrade. The album was made of instrumental compositions for viola caipira (Brazilian Ten String Guitar), an instrument that he played with a great virtuosity. This was the beginning of a one of a kind production in Brazil that ended up creating a new segment in the field of a genre known as "Música Caipira". As a result of the Brazilian's Popular Music formal and aesthetic transformations, ever since the seventies, Renato Andrade's work reflects the emergence of fine lines between the popular and the classical. In order to compose their plays, composers and musicians searched for Brazilian popular traditions so they could give to them "authenticity" and "legitimacy". At the same time, they adopt classic procedures to make the plays coherent and dense. This dissertation has the intent to explore Renato Andrade's work. It aims to expose the musical elements used in his compositions and his musical influences and tendencies and also, the construction of a specific style of the author, either through his music or through his ten string Brazilian guitar execution. To do that, we researched his biography and his music production in order to understand his creative procedures, his way to organize the musical materials in the Ten String Guitar and, finally, the consolidation of what we call his compositional language. On a second moment, we describe Renato Andrade as a performer: his performance on stage, and the construction of the "character" Renato Andrade / Mestrado / Fundamentos Teoricos / Mestre em Música
696

String diagram rewriting : applications in category and proof theory / Réécriture des diagrammes : applications à la théorie des catégories et à la théorie de la démonstration

Acclavio, Matteo 14 December 2016 (has links)
Dans le dernier siècle, nombreux sciences ont enrichi leur syntaxe pour pouvoir modeler des interactions. Entre eux on peut compter l'informatique, la physique quantique, et aussi la biologie et l’économie : toutes ces sciences sont des exemples de domaines qui ont besoin d'une syntaxe et d'une sémantique soit pour la concurrence que pour la séquentialité.Les diagrammes des cordes sont bien adapté à cet effet. Dans leur syntaxe on peut retrouver deux compositions : une composition parallèle et une composition séquentielle, qui peuvent interagir à travers une loi d'interchange. Si on considère cette loi comme une égalité, les diagrammes de cordes sont une syntaxe pour les catégories monoidales strictes, avec une représentation graphique plus intuitive que les formules algébriques traditionnelles.Dans cette thèse, on étude cette syntaxe de dimension 2 et sa sémantique. On considéré la réécriture des diagrammes et on donne des applications de cet méthode :- une preuve détaillée du théorème de cohérence de MacLanes pour les catégories monoidales symétriques basée sur un système de réécriture convergent donnée en arXiv:1606.01722;;- une interprétation des dérivations de preuves avec les diagrammes de preuve pour le fragment MELL de la logique linéaire, qui capture l’équivalence de preuves. On peut vérifier la séquentialité en temps linéaire, c'est à dire vérifier si un diagramme corresponds à une preuve. Cette interprétation est une extension de celle pour le fragment MLL donnée en arXiv:1606.09016 en donnant aussi un résultat de élimination du coupure. / In the last century, several sciences enriched their syntax in order to model interactions.Not only computer science and quantum physics, but also biology and economicsare examples of fields requiring syntax and semantics for concurrency as wellas for sequentiality.String diagrams are suitable for that purpose. In that syntax, we have two compositions:the parallel one and the sequential one, which may interact by the interchangerule. If we consider this rule as an equality, string diagrams are a syntax for strictmonoidal categories, with a more intuitive graphical representation than traditionalalgebraic formulas.In this thesis, we study this 2-dimensional syntax and its semantics. We considerdiagram rewriting and we give two applications of those methods:• a detailed proof of Mac Lane’s coherence theorem for symmetric monoidal categoriesbased on convergent diagram rewriting, which is given in arXiv:1606.01722;• an interpretation of proof derivations by string diagrams for the MELL fragmentof linear logic, which captures proof equivalence. We get a linear sequentializabilitytest to verify if a diagram corresponds to a proof . This interpretationextends the one for the MLL fragment given in arXiv:1606.09016,providing also a cut-elimination result.
697

Flux backgrounds, AdS/CFT and Generalized Geometry / Milieux de flux, Ads/CFT et géométrie généralisée

Ntokos, Praxitelis 23 September 2016 (has links)
La recherche de solutions du vide en présence de flux non-triviaux dans la théorie des cordes est importante pour la construction de modèles pertinents à la phénomenologie de la physique des particules. Dans le cadre de la correspondance AdS/CFT, les théories de jauge en 4d, considérées comme descendantes de N=4 SYM, sont duales à des configurations de champs en 10d avec des géometries ayant un facteur AdS_5 asymptotiquement. Dans cette thèse, nous étudions des déformations de masse qui brisent la supersymétrie (partiellement ou totalement) du côté de la théorie des champs et qui sont duales aux états de la théorie IIB avec flux non-nuls du côté gravitique. Les équations du mouvement de la supergravité contraignent les paramètres de la théorie de jauge à satisfaire certaines relations. En particulier, nous trouvons que la somme des carrés de la masse des bosons est égale à celle fermions, rendant ces modèles problematiques pour des applications phénomenologiques. L'étude des théories duales de supergravité pour des déformations plus générales de la théorie conforme des champs exige des techniques qui vont au-delà des outils géometriques standards. La Géometrie Généralisée Exceptionelle fournit une façon très élégante d'intégrer les flux de supergravité dans la géometrie. Nous examinons les solutions AdS_5 avec des flux génériques conservants huit supercharges et nous montrons que celles-ci satisfont des relations particulièrement simples qui ont une interprétation géometrique dans le cadre de la Géometrie Généralisée. Ceci ouvre la voie pour l'étude systématique des déformations marginales supersymétriques de la théorie / The search for string theory vacuum solutions with non-trivial fluxes is of particular importance for the construction of models relevant for particle physics phenomenology. In the framework of the AdS/CFT correspondence, four-dimensional gauge theories which can be considered to descend from N = 4 SYM are dual to ten- dimensional field configurations with geometries having an asymptotically AdS_5 factor. In this Thesis, we study mass deformations that break supersymmetry (partially or entirely) on the field theory side and which are dual to type IIB backgrounds with non-zero fluxes on the gravity side. The supergravity equations of motion constrain the parameters on the gauge theory side to satisfy certain relations. In particular, we find that the sum of the squares of the boson masses should be equal to the sum of the squares of the fermion masses, making these set-ups problematic for phenomenology applications. The study of the supergravity duals for more general deformations of the conformal field theory requires techniques which go beyond the standard geometric tools. Exceptional Generalized Geometry provides a very elegant way to incorporate the supergravity fluxes in the geometry. We study AdS_5 backgrounds with generic fluxes preserving eight supercharges and we show that these satisfy particularly simple relations which admit a geometrical interpretation in the framework of Generalized Geometry. This opens the way for the systematic study of supersymmetric marginal deformations of the conformal field theory in the context of AdS/CFT.
698

De l'intérêt des modèles grammaticaux pour la reconnaissance de motifs dans les séquences génomiques / Interest of grammatical models for pattern matching in genomic sequences

Antoine-Lorquin, Aymeric 01 December 2016 (has links)
Cette thèse en bioinformatique étudie l'intérêt de rechercher des motifs dans des séquences génomiques à l'aide de grammaires. Depuis les années 80, à l'initiative notamment de David Searls, des travaux ont montré qu'en théorie, des grammaires de haut niveau offrent suffisamment d'expressivité pour permettre la description de motifs biologiques complexes, notamment par le biais d'une nouvelle classe de grammaire dédiée à la biologie : les grammaires à variables de chaîne (SVG, String Variable Grammar). Ce formalisme a donné lieu à Logol, qui est un langage grammatical et un outil d'analyse développé dans l'équipe Dyliss où a lieu cette thèse. Logol est un langage conçu pour être suffisamment flexible pour se plier à une large gamme de motifs qu'il est possible de rencontrer en biologie. Le fait que les grammaires restent inutilisée pour la reconnaissance de motifs pose question. Le formalisme grammatical est-il vraiment pertinent pour modéliser des motifs biologiques ? Cette thèse tente de répondre à cette question à travers une démarche exploratoire. Ainsi, nous étudions la pertinence d'utiliser les modèles grammaticaux, via Logol, sur six applications différentes de reconnaissance de motifs sur des génomes. Au travers de la résolution concrète de problématiques biologiques, nous avons mis en évidence certaines caractéristiques des modèles grammaticaux. Une de leurs limites est que leur utilisation présente un coût en termes de performance. Un de leurs atouts est que leur expressivité couvre un large spectre des motifs biologiques, contrairement aux méthodes alternatives, et d'ailleurs certains motifs modélisés par les grammaires n'ont pas d'autres alternatives existantes. Il s'avère en particulier que pour certains motifs complexes, tels que ceux alliant séquence et structure, l'approche grammaticale est la plus adaptée. Pour finir, l'une des conclusions de cette thèse est qu'il n'y a pas réellement de compétition entre les différentes approches, mais plutôt qu'il y a tout à gagner d'une coopération fructueuse. / This thesis studies the interest to look for patterns in genomic sequences using grammars. Since the 80s, work has shown that, in theory, high level grammars offer enough expressivity to allow the description of complex biological patterns. In particular David Searls has proposed a new grammar dedicated to biology: string variable grammar (SVG). This formalism has resulted in Logol, a grammatical language and an analysis tool developed by Dyliss team where this thesis is taking place. Logol is a language designed to be flexible enough to express a wide range of biological patterns. The fact that the grammars remain unknown to model biological patterns raises questions. Is the grammatical formalism really relevant to the recognition of biological patterns? This thesis attempts to answer this question through an exploratory approach. We study the relevance of using the grammatical patterns, by using Logol on six different applications of genomic pattern matching. Through the practical resolution of biological problems, we have highlighted some features of grammatical patterns. First, the use of grammatical models presents a cost in terms of performance. Second the expressiveness of grammatical models covers a broad spectrum of biological patterns, unlike the others alternatives, and some patterns modeled by grammars have no other alternative solutions. It also turns out that for some complex patterns, such as those combining sequence and structure, the grammatical approach is the most suitable. Finally, a thesis conclusion is that there was no real competition between different approaches, but rather everything to gain from successful cooperation.
699

Musical Citizens: String Teachers' Perceptions of Citizenship Education in the Private Studio

Harrison, Joan January 2013 (has links)
This quantitative study explores string teachers’ perceptions of citizenship education and its use in the private lesson. Guided by Westheimer and Kahne’s (2004) model of citizenship education the study sought to identify (a) how private string teachers perceive citizenship education, and (b) the factors that influence these perceptions. Four hundred and fifteen (415) members of the American String Teachers Association (ASTA) participated in this study by completing an on-line survey that contained both closed and open-ended questions. The resulting data was coded and organized according to the survey questions and the conceptual framework. Research findings revealed that, although teachers did not explicitly consider citizenship education a part of their lessons, their intentions and their report on pedagogical practices could be described as citizenship education when viewed through the conceptual framework used in the study. Indeed, nearly all of the participant responses revealed intentions to include attributes of what Westheimer and Kahne refer to as the Personally Responsible Citizen in their music lessons with students. Educating for traits of other types of citizenship was also reported. Factors deemed influential in string teachers’ perceptions of citizenship education included the following: If the teachers had earned certification in Suzuki pedagogy; the number of years of teaching experience; if teachers self-identified as primarily educators, performers, or both; the age of the students who are taught. Additionally, the study addresses teachers’ statements about the use of competitions, dialogue in lessons, and general attitudes about the appropriateness of citizenship education in several different learning environments. The study findings add to a small but growing body of research that furthers understandings of the links between citizenship education and music education. In addition, the findings contribute to our understanding of the complexity of the relationship between private teachers and their students.
700

Results in perturbative quantum supergravity from string theory / Résultats perturbatifs dans les théories de supergravité quantique par la théorie des cordes

Tourkine, Piotr 09 June 2014 (has links)
Les théories de supergravité sont des extensions supersymmetriques de la relativité générale (RG) d'Einstein. Leur comportement ultraviolet (UV) est meilleur que celui de la RG car les contributions bosoniques et fermioniques se compensent dans les diagrammes en boucles. La supergravité maximale a le meilleur comportement UV, toutefois les prédictions les plus précises venant aussi bien de la théorie des champs que de la théorie des cordes indiquent que la théorie devrait elle aussi souffrir de divergences UV, à partir de 7 boucles. Cette question ouverte constitue un cadre dans lequel peut être problématisés ma thèse. En général, l'approche que j'ai suivie consiste à étudier les amplitudes de diffusion en théorie des cordes dans la limite ou la longueur de la corde devient nulle; on s'attend ainsi à retrouver les amplitudes de diffusion de supergravité. Curieusement, on sait très peu de choses sur cette limite au délà d'une boucle. Une part importante de mon travail thèse a consisté à développer des outils mathématiques basés sur la géométrie tropicale pour décrire cette limite en genre deux et au délà. Afin de tester la précision des prédiction de la théorie des cordes, dans ma thèse j'ai aussi travaillé sur le comportement UV des théories de supergravité demi-maximale. Nous avons montré un théorème de non-renormalisation qui expliqué l'absence de divgerence à 3 boucles et en prédit une à 4 boucles. Enfin je me suis intéressé aux techniques utilisées en théorie des champs pour calculer ces amplitudes à haut nombre de boucles en théorie des champs, et notament à la "double copie BCJ", dont avons proposé la première analyse à une boucle depuis la théorie des cordes. / Supergravity theories are supersymmetric extensions of General Relativity (GR). They have a better ultraviolet (UV) behavior than GR, due to cancellations between bosons and fermions in loop diagrams. Maximal supergravity is a candidate for a UV finite point-like theory of quantum gravity. Nowadays, the most advanced understanding coming from field theory and string theory indicate that the theory should not be UV finite, and that the first UV divergences should appear at the 7-loop order. This open question constitutes a background in which my PhD thesis can be problematized.In this thesis, our approach consists in using string theory scattering amplitudes and study their point-like limit, in which supergravity amplitudes are expected to be recovered. Very little is known beyond one loop on this limit and in this manuscript I describe first how a recent field of mathematics, tropical geometry, may be used in this process, and mention some applications and open issues.Another way to cross-check the predictions of string theory on the UV behavior of maximal supergravity consists in performing the same analysis in theories of reduced supersymmetry.I discuss the case of half-maximal supergravity theories, and show a non-renormalization theorem in heterotic string which explains the vanishing of the 3-loop divergence of this theory and predicts a 4-loop divergence.The last aspect of my work is focused on a string theoretic understanding on the techniques used in field theory to compute higher loop amplitudes. I describe the first analysis of the so called BCJ double copy construction at one-loop from string theory, and partly explain the origin of the BCJ prescription.

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