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Inflationary Cosmology in Scalar-Tensor Theories / スカラー・テンソル理論におけるインフレーション宇宙論Domenech, Fuertes Guillem 25 September 2017 (has links)
京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第20656号 / 理博第4321号 / 新制||理||1621(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 佐々木 節, 教授 田中 貴浩, 教授 川合 光 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM
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Sur certaines propriétés de l'Energie Noire / On Some Properties of Dark EnergyRanquet, André 17 December 2010 (has links)
Les résultats des observations cosmologiques réalisées à la charnière du siècle (SN1A, CMB, BAO) montrent que contrairement aux prévisions du modèle standard, l'expansion de l'Univers est actuellement en train de s'accélérer. Pour rendre compte de ce phénomène, un composant inconnu dénommé "énergie noire" (Dark Energy) a été introduit soit directement comme un fluide de pression négative, soit indirectement en modifiant la Relativité générale. Après avoir présenté le cadre général de la description de l'Univers, ainsi que le modèle cosmologique standard actuellement accepté, la présente thèse étudie les interactions possibles entre l'énergie noire et une éventuelle courbure de l'espace, en s'intéressant plus particulièrement aux cas où l'incertitude sur la courbure peut falsifier la nature "fantôme" de cette énergie noire. Dans un deuxième temps, la possibilité d'obtenir un comportement de type énergie noire au moyen d'une modification de la Relativité générale est abordée en faisant appel aux théories scalaire-tenseur. Les conditions générales de viabilité de ces théories sont présentées, ainsi que les conditions d'existence d'énergie noire, normale et fantôme. Enfin la possibilité de mettre en évidence cette énergie noire d'origine scalaire-tenseur par des mesures dans le Système solaire est étudiée en utilisant le formalisme de l'analyse post-newtonienne paramétrée. / The results of the cosmological observations at the turn of the century (SN1a, CMB, BAO) show that, in contrast to the predictions of the standard model, the Universe expansion is presently accelerating. To account for this fact, an unknown component dubbed "dark energy" was introduced either directly as a fluid with negative pressure, or indirectly as a modification of General Relativity.After the presentation of the general frame of the Universe description, and of the presently accepted cosmological standard model, we study the interactions between dark energy and a possible spatial curvature, with special attention to the cases where the curvature uncertainty may falsify the phantom nature of dark energy. In a second step we consider a modification of General Relativity, the Scalar-Tensor theories, as a way to generate dark energy. The general viability conditions for these theories are presented, as well as the conditions for the presence of normal and phantom dark energy. In particular we study the possibility to detect this Scalar-Tensor dark energy with measurements within the Solar System using the Parametrised Post-Newtonian formalism.
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Teoria escalar-tensorial: Uma abordagem geométricaAlmeida, Tony Silva 29 July 2014 (has links)
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Previous issue date: 2014-07-29 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / In this cool thesis, we consider an approach to Brans-Dicke theory of gravity in which the
scalar eld has a geometrical nature. By postulating the Palatini variation, we nd out
that the role played by the scalar eld consists in turning the space-time geometry into a
Weyl integrable manifold. This procedure leads to a scalar-tensor theory that di ers from
the original Brans-Dicke theory in many aspects and presents some new features. We
also consider the Weyl integrable geometry to investigate gravity in (2+1)-dimensions.
We show that, in addition to leading to a Newtonian limit, WIST in (2+1) dimensions
presents some interesting properties that are not shared by Einstein theory, such as geodesic
deviation between particles in a dust distribution. Finally, taking advantage of the
duality between the geometrical scalar-tensor theory and general relativity coupled with
a massless scalar eld we study naked singularities and wormholes. / Esta tese trata de tópicos relacionados às teorias escalares-tensoriais e a geometria de
Weyl integrável. Nossa abordagem será no sentido de indicar a geometria de Weyl integr
ável como sendo um ambiente natural para a introdução de teorias escalares-tensorias.
Nossa discussão será em torno da teoria de Brans-Dicke, considerada o protótipo das teorias
escalares tensoriais, no entanto a discussão é facilmente estendida para essas versões
mais gerais. Fazemos isso em dois momentos. Primeiro, indicando, no âmbito da teoria
de Brans-Dicke, que na estrutura geométrica e de campos adotadas pela teoria existe
uma relação estreita com a geometria de Weyl, inclusive associando o efeito descrito na
literatura como "quinta força"(que violaria o princípio de equivalência) com o movimento
geodésico da geometria de Weyl integrável, reformulando o postulado geodésico. E, num
segundo momento, usando o método variacional de Palatini, acabamos por formular uma
nova teoria escalar-tensorial, agora com ingredientes completamente geométricos, ambientada
numa geometria de Weyl integrável. Estudamos ainda soluções no vazio do problema
estático de uma distribuição de massa esfericamente simétrica, onde surgem objetos de
interesse astrofísico como singularidades nuas e buracos de minhoca. Também formulamos
a teoria conhecida por WIST (Weyl Integrable Spacetimes) em (2 + 1)D, o que resulta
numa teoria consistente, não sofrendo das falhas associadas à teoria da relatividade geral
nessa dimensionalidade
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