京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第20900号 / 理博第4352号 / 新制||理||1625(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 田中 貴浩, 教授 向山 信治, 教授 川合 光 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

Gravitational waves are truly transparent to matter in the Universe and carry the information of the very early epoch. We show that the energy density spectrum of the primordial gravitational waves has characteristic features due to the successive changes in the relativistic degrees of freedom during the radiation era. Our calculations are solely based on the standard model of cosmology and particle physics, and therefore these features must exist. Our calculations significantly improve the previous ones which ignored these effects and predicted a smooth, featureless spectrum. Going back in time to the beginning of the radiation era, reheating of the Universe must have taken place after inflation for primordial nucleosynthesis to begin. We show that reheating occurs spontaneously in a broad class of inflation models with [scientific symbols] gravity (Ø is inflaton). The model does not require explicit couplings between Ø and bosonic or fermionic matter fields. The couplings arise spontaneously when Ø settles in the vacuum expectation value (vev) and oscillates. This mechanism allows inflaton quanta to decay into any fields which are not conformally invariant in [scientific symbols] gravity theories. Applying the above method, we study implications of the large-N species solution to the hierarchy problem, proposed by G. Dvali, for reheating after inflation. We show that, in this scenario, the decay rates of inflaton fields through gravitational decay channels are enhanced by a factor of N, and thus they decay into N species of the quantum fields very efficiently. Without violating energy conservation, cosmological consideration places non-trivial constraints on Dvali's solution to the hierarchy problem. Going back in time still further, we study the period just before the beginning of reheating, the era of coherent oscillation of scalar fields. We show that non-Gaussian primordial curvature perturbations appear temporarily in the coherent oscillation phase after multi-field inflation. We directly solve the evolution equation of non-Gaussianity on super-horizon scales caused by the non-linear influence of entropy perturbations on the curvature perturbations during this phase. We show that our approach precisely matches with the so-called "separate universe approach" or "δN formalism" by studying a simple quadratic two-field potential. / text

No description available.

Les prédictions d'inflation du spectre de puissance de la perturbation de la courbure ont déjà fait l’objet de vérification d’un excellent niveau, permettant à de nombreux modèles de rester compatibles avec les observations. Dans la présente thèse, nous avons étudié les corrélations de troisième ordre qui pourraient permettre de mieux distinguer les différents modèles d'inflation les uns des autres. Parmi toutes les extensions possibles du modèle standard d'inflation, nous avons choisi d'étudier des modèles de deux champs scalaires à termes cinétiques standards et à métrique des champs plat. La nouveauté introduite par ces modèles est la présence de la perturbation d'isocourbure. Son interaction avec la perturbation adiabatique hors de l'horizon produit des non-linéarités caractéristiques des modèles à plusieurs champs scalaires. Dans, ce contexte, nous avons établi la forme de la perturbation adiabatique et de la perturbation d'isocourbure invariant sous transformations de jauge en deuxième ordre. De plus, nous avons trouvé l'action de troisième ordre qui décrit leurs interactions. En outre, nous avons élaboré le formalisme des grandes longueurs d'onde afin d'obtenir une expression pour le paramètre de non-gaussiannité fNL en fonction du potentiel des champs. Nous avons ensuite, utilisé cette formule pour traiter analytiquement - avec l'hypothèse de slow-roll - des classes générales de potentiels et vérifier nos résultats numériquement par la théorie exacte. De là, nous avons pu tirer des conclusions générales concernant les propriétés de fNL, comme par exemple la dépendance de sa magnitude des caractéristiques du trajet des champs et de la perturbation d'isocourbure, ainsi que sa dépendance de la magnitude et de la taille relative des trois impulsions dont le corrélateur à trois points est fonction. / Inflationary predictions for the power spectrum of the curvature perturbation have been verified to an excellent degree, leaving many models compatible with observations. In this thesis we studied third-order correlations, that might allow one to further distinguish between inflationary models. From all the possible extensions of the standard inflationary model, we chose to study two-field models with canonical kinetic terms and flat field space. The new feature is the presence of the so-called isocurvature perturbation. Its interplay with the adiabatic perturbation outside the horizon gives birth to non-linearities characteristic of multiple-field models. In this context, we established the second-order gauge-invariant form of the adiabatic and isocurvature perturbation and found the third-order action that describes their interactions. Furthermore, we built on and elaborated the long-wavelength formalism in order to acquire an expression for the parameter of non-Gaussianity fNL as a function of the potential of the fields. We next used this formula to study analytically, within the slow-roll hypothesis, general classes of potentials and verified our results numerically for the exact theory. From this study, we deduced general conclusions about the properties of fNL, its magnitude depending on the characteristics of the field trajectory and the isocurvature component, as well as its dependence on the magnitude and relative size of the three momenta of which the three-point correlator is a function.

A cosmologia inflacionária descreve uma fase durante a qual o nosso universo passou por expansão acelerada em um curto período de tempo a escalas de altas energias. A inflação soluciona os problemas deixados pelo modelo cosmológico da Grande Explosão, tais como os problemas de planura e do horizonte. Nesta fase, o nosso universo era governado por um potencial V(Ø) gerado por um campo escalar inflaton, Ø(t). este potencial deve obedecer às condições de rolagem lenta dadas por {, |n|} 1, onde e n são os parâmetros de rolagem lenta. A cosmologia de branas inspira-se na teoria de cordas descrevendo modelos cosmológicos com dimensões extras. Sua grande ascensão aconteceu com a publicação de dois trabalhos de Randall e Sundrum na década de 90. Estes dois modelos consideram um espaço-tempo AdS5 no qual está inserido uma hipersuperfície 3-dimensional chamada 3-brana (nosso universo). As partículas e forças do modelo padrão estão confinadas nesta 3-brana enquanto o gráviton pode viajar por todo o espaço-tempo. O modelo RS-I considera duas 3-branas que delimitam a dimensão extra enquanto o modelo RS-II considera uma única 3-brana e o tamanho da dimensão extra é infinito. O objetivo deste trabalho é unir estas duas cosmologias de modo que possamos estudar inflação em modelos de branas. Escolhemos a cosmlogia de branas do tipo RS-I para exempleficarmos três potenciais condidatos a gerarem inflação em nosso universo. Para a aceitação de um modelo inflacionário representado por V (Ø), devemos calcular o índice espectral n(k) e sua derivada em relação ao número de onda k, dn(k)/dlnk, deste potencial, e comparar estes resultados teóricos com os dados experimentais do WMAP. É isto que faremos com estes três potenciais / An inflationary cosmology describles a phase in which ou Universe goes through accelerated expansion in a short time period at high energy scales. Inflation solves problems left by the Standard Big Bang cosmological model such as problems of flatness and horizon. In this phase, our Universe is ruled by a potential V(Ø) generated bya an inflaton scalar field Ø(t). This potential generated must obey conditions of slow roll given by {, |n|}1, and n are the parameters of slow roll. A brane cosmology was inspired by a string describing cosmological models with extra dimensions. An interest to it highly arose with a publication of two papers by Randall and Sundrum in the 90s. These two models consider a space-time AdS5 in which the hipersurface with three spacial dimensions is inserted. This hypersurface (our Universe) is called a 3-brane. Particles and forces of the standard model are inserted in this 3-brane whereas the graviton can move through all space-time. In the RS-I model one considers two three-brane which delimit an extra dimension whereas in the RS-II model one consideres a unique 3-brane ande the size of the extra dimension is infinite. The aim of this ork is to unify these two cosmologies in a way which would allow studying inflation in brane models. We choose a cosmology in RS-I branes to exemplify three candidate potentials to generate inflation in our Universe. In order to accept an inflationary model represented by V (Ø), we shold calculate the spectral index n(k)/d/lnk, for this potential, and compare these theoretical results with the available experimental data fo WMAP. These studies will be carried out for the three potentials above mentioned.

Thesis (Ph.D.)--Tufts University, 1999. / Adviser: Alexander Vilenkin. Submitted to the Dept. of Physics. Includes bibliographical references (leaves 119-122). Access restricted to members of the Tufts University community. Also available via the World Wide Web;

Honors Project--Smith College, Northampton, Mass., 2009. / Includes bibliographical references (p. 35).

Thesis (Ph. D.)--University of Oxford, 1988. / Includes bibliographical references (leaves 425-438).

Thesis (Ph. D.)--University of Illinois at Urbana-Champaign, 1995. / Vita. Includes bibliographical references.

Orientador: Alberto Vazquez Saa / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-13T05:40:24Z (GMT). No. of bitstreams: 1 Froes_AndreLuisDelvas_M.pdf: 1355314 bytes, checksum: edf9f0fa41f3a8e6e519f2b958be6603 (MD5) Previous issue date: 2009 / Resumo: O foco do presente trabalho é a realização de períodos inflacionários baseados em campos vetoriais. Os conhecimentos necessários para atingir esse objetivo foram introduzidos de maneira sistemática, na ordem em que o autor julgou mais lógica. No primeiro capítulo são descritos numerosos detalhes acerca de nosso Universo e da capacidade atual de observá-lo. No segundo, apresenta-se o modelo cosmológico padrão. São também apresentados os alguns dos principais resultados da Relatividade Geral, a partir dos quais constroem-se os fundamentos teóricos da Cosmologia. No terceiro capítulo a teoria in acionária é estudada, e são comentados seus resultados mais importantes e modelos mais conhecidos, baseados em campos escalares. No quarto capítulo inicia-se o estudo de períodos in acionários utilizando campos vetoriais. Esse assunto despertou a atenção e gerou diversas publicações ao longo do ano de 2008. Por fim, são apresentadas as impressões do autor e as perspectivas futuras da área são delineadas. / Abstract: The main point of the present work is the realisation of in ationary periods based on vector fields. The knowledge needed to achieve this objective were introduced in a systematic manner, in the order that the author found more logical. In the first chapter numerous details about our universe and the present capacity to observe it were described. In the second, the standard model of cosmology is presented. Some of the most important results of General Relativity and observational cosmology are also presented, and on these grounds the theoretical fundaments of Cosmology are estabilished. In the third chapter in ationary cosmology is studied, and its most important results and some well known models based on scalar fields are presented. In the fourth chapter begins the study of in ationary periods that uses vector fields. This subject attracted attention and generated many papers in the year of 2008. At last, the author¿s impressions and future perspectives in the subject are presented. / Mestrado / Cosmologia / Mestre em Física