Made available in DSpace on 2015-03-03T15:15:24Z (GMT). No. of bitstreams: 1 ThiagoBRFO_DISSERT.pdf: 776732 bytes, checksum: 79a4002c3c2d724d3d1651680816802b (MD5) Previous issue date: 2010-07-01 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / In this dissertation, after a brief review on the Einstein s General Relativity Theory and its application to the Friedmann-Lemaitre-Robertson-Walker (FLRW) cosmological models, we present and discuss the alternative theories of gravity dubbed f(R) gravity. These theories come about when one substitute in the Einstein-Hilbert action the Ricci curvature R by some well behaved nonlinear function f(R). They provide an alternative way to explain the current cosmic acceleration with no need of invoking neither a dark energy component, nor the existence of extra spatial dimensions. In dealing with f(R) gravity, two different variational approaches may be followed, namely the metric and the Palatini formalisms, which lead to very different equations of motion. We briefly describe the metric formalism and then concentrate on the Palatini variational approach to the gravity action. We make a systematic and detailed derivation of the field equations for Palatini f(R) gravity, which generalize the Einsteins equations of General Relativity, and obtain also the generalized Friedmann equations, which can be used for cosmological tests. As an example, using recent compilations of type Ia Supernovae observations, we show how the f(R) = R ? fi/Rn class of gravity theories explain the recent observed acceleration of the universe by placing reasonable constraints on the free parameters fi and n. We also examine the question as to whether Palatini f(R) gravity theories permit space-times in which causality, a fundamental issue in any physical theory [22], is violated. As is well known, in General Relativity there are solutions to the viii field equations that have causal anomalies in the form of closed time-like curves, the renowned G?del model being the best known example of such a solution. Here we show that every perfect-fluid G?del-type solution of Palatini f(R) gravity with density and pressure p that satisfy the weak energy condition + p 0 is necessarily isometric to the G?del geometry, demonstrating, therefore, that these theories present causal anomalies in the form of closed time-like curves. This result extends a theorem on G?del-type models to the framework of Palatini f(R) gravity theory. We derive an expression for a critical radius rc (beyond which causality is violated) for an arbitrary Palatini f(R) theory. The expression makes apparent that the violation of causality depends on the form of f(R) and on the matter content components. We concretely examine the G?del-type perfect-fluid solutions in the f(R) = R?fi/Rn class of Palatini gravity theories, and show that for positive matter density and for fi and n in the range permitted by the observations, these theories do not admit the G?del geometry as a perfect-fluid solution of its field equations. In this sense, f(R) gravity theory remedies the causal pathology in the form of closed timelike curves which is allowed in General Relativity. We also examine the violation of causality of G?del-type by considering a single scalar field as the matter content. For this source, we show that Palatini f(R) gravity gives rise to a unique G?deltype solution with no violation of causality. Finally, we show that by combining a perfect fluid plus a scalar field as sources of G?del-type geometries, we obtain both solutions in the form of closed time-like curves, as well as solutions with no violation of causality / Nesta disserta??o, ap?s uma breve revis?o sobre a Teoria da Relatividade Geral de Einstein e suas aplica??es para os modelos cosmol?gicos de Friedmann-Lemaitre- Robertson-Walker (FLRW), apresentamos e discutimos as teorias alternativas de gravidade denominadas de gravidade f(R). Estas teorias surgem quando substitu?mos na a??o de Einstein-Hilbert o escalar de curvatura de Ricci R por qualquer fun??o f(R) n?o-linear bem comportada. Elas fornecem uma maneira alternativa para explicar a acelera??o c?smica atual sem necessitar envolver qualquer componente de energia escura ou a exist?ncia de dimens?es espaciais extras. Quando lidamos com gravidade f(R), dois diferentes princ?pios variacionais podem ser seguidos, a saber, o formalismo m?trico e o de Palatini, os quais levam a equa??es de movimento muito diferentes. Descrevemos brevemente o formalismo m?trico e ent?o nos concentramos no princ?pio variacional de Palatini para a a??o da gravidade. Fazemos uma deriva??o sistem?tica e detalhada das equa??es de campo para a gravidade f(R) de Palatini, as quais generalizam as equa??es de Einstein da Relatividade Geral. Em seguida obtemos as equa??es de Friedmann generalizadas, que podem ser usadas para testes cosmol?gicos. Para exemplificar, usamos compila??es recentes de observa??es de supernovas do tipo Ia e mostramos como a classe de teorias de gravidade f(R) = R ? /Rn explica a recente acelera??o observada do universo quando colocamos v?nculos razo?veis sobre os par?metros livres e n. Examinamos tamb?m a quest?o de como teorias f(R) de gravidade em Palatini permitem espa?os-tempos em que a causalidade, um resultado fundamental em qualquer teoria f?sica [22], ? violada. Como ? bem conhecido, na Relatividade Geral existem solu??es para as equa??es de campo que possuem anomalias causais na forma de curvas tipo-tempo fechadas, sendo o modelo de G?del o exemplo mais bem conhecido de tais solu??es. Aqui mostramos que toda solu??o do tipo-G?del de gravidade f(R) em Palatini com fluido perfeito, caracterizado por densidade e press?o p, satisfazendo a condi??o de energia fraca + p 0, ? necessariamente isom?trica ? geometria de G?del, demonstrando, portanto, que essas teorias apresentam anomalias causais na forma de curvas tipo-tempo fechadas. Esses resultados ampliam um teorema sobre modelos tipo-G?del para a estrutura das teorias de gravidade f(R) de Palatini. Derivamos uma express?o para o raio cr?tico rc (al?m do qual a causalidade ? violada) para uma teoria arbitr?ria de gravidade f(R) de Palatini. A express?o encontrada tornou claro que a viola??o da causalidade depende da forma de f(R) e dos componentes do conte?do de mat?ria. Examinamos objetivamente as solu??es tipo-G?del de um fluido perfeito na classe f(R) = R ? /Rn das teorias de gravidade de Palatini e mostramos que, para uma densidade de mat?ria positiva e para e n em um intervalo permitido pelas observa??es, essas teorias n?o admitem como solu??es de suas equa??es de campo a geometria de G?del juntamente com um fluido perfeito. Nesse sentido, teorias de gravidade f(R) remediam a patologia causal na forma de curvas tipotempo fechadas que ? permitido na Relatividade Geral. Examinamos tamb?m essa viola??o de causalidade ao considerar um campo escalar como conte?do material. Para essa fonte, mostramos que a gravidade f(R) em Palatini d? origem a uma ?nica solu??o do tipo-G?del sem viola??o de causalidade. Finalmente, mostramos que a combina??o de um fluido perfeito mais um campo escalar como fontes de geometrias tipo-G?del, levam a solu??es na forma de curvas tipo-tempo fechadas como a solu??es sem viola??o de causalidade

Dans ce manuscrit, nous présentons un mise en place et calcul d'un observable physique dans le cadre de la Gravité Quantique à Boucles covariante, pour un processus physique mettant en jeu la gravité quantique de façon non-perturbatif. Nous considerons la transition d'une région de trou noir à une région de trou blanc, traitée comme une transition de géométrie assimilable à un effet de tunnel gravitationnel. L'observable physique est le temps caractéristique dans lequel ce processus se déroule.Nous commençons par une dérivation formelle de haut--en--bas, allant de l'action de Hilbert-Einstein au ansatz qui définit les amplitudes de l'approche covariante de la GQB. Nous prenons ensuite le chemin de bas--en--haut, aboutissant à l'image d'une intégrale de chemin du type somme-de-géométries qui émerge à la limite semi-classique, et discutons son lien étroite avec une intégrale de chemin basé sur l'action de Regge. En suite, nous expliquons comment construire des paquets d'ondes décrivant des géométries spatiales quantiques, plongées dans un espace-temps quantique de signature Lorentzienne.Nous montrons que lors de la mise en œuvre de ces outils, nous avons une estimation simple des amplitudes décrivant des transitions de géométrie de façon probabiliste. Nous construisons un mise en place basée sur l'espace-temps Haggard-Rovelli, où une approche d'intégrale de chemin peut être appliquée naturellement. Nous procédons à une dérivation d'une expression explicite, analytiquement bien--définie et finie, pour une amplitude de transition décrivant ce processus. Nous utilisons ensuite l'approximation semi-classique pour estimer le temps caractéristique du phénomène. / In this manuscript we present a calculation from covariant Loop Quantum Gravity, of a physical observable in a non-perturbative quantum gravitational physical process. The process regards the transition of a trapped region to an anti--trapped region and is treated as a quantum geometry transition akin to gravitational tunneling. The physical observable is the characteristic timescale in which the process takes place. We start with a top--to--bottom formal derivation of the ansatz defining the amplitudes for covariant LQG, starting from the Hilbert-Einstein action. We then take the bottom--to--top path, starting from the EPRL ansatz, to the sum--over--geometries path integral emerging in the semi-classical limit, and discuss its close relation to the naive path integral over the Regge action. We proceed to the construction of wave--packets describing quantum spacelike three-geometries that include a notion of embedding in a Lorentzian spacetime. We derive a simple estimation for the amplitudes describing geometry transition and show that a probabilistic description for such phenomena emerges, with the probability of the phenomena to take place being in general non-vanishing.The Haggard-Rovelli spacetime, modelling the spacetime surrounding the geometry transition region for a black to white hole process, is formulated. We then use the semi--classical approximation to give a general estimation of amplitudes describing the process. We conclude that the transition is predicted to be allowed by LQG, with a crossing time that is linear in the mass. The probability for the process to take place is suppressed but non-zero.

The role of dopamine in directly modulating somatic motoneuron excitability and hence muscle tone is unknown. We investigated whether dopamine influences the trigeminal motor pool (MoV) that innervates the masseter and tensor palatini muscles, both of which function to maintain upper airway patency. We hypothesized that dopamine facilitates motor outflow at the MoV. We focally applied apomorphine (nonspecific dopamine receptor agonist) at the MoV in anaesthetized rats. We also applied receptor-specific agonists and antagonists to determine the receptor subtype mediating dopaminergic mechanisms of action. We demonstrated that dopaminergic transmission at the MoV potently increased motor outflow via the D1-like receptor and facilitated masseter and tensor palatini muscle tone. It is unknown whether endogenous dopamine release on to airway motoneurons influences their activity to regulate muscle tone in natural sleep-wake behaviours. This issue warrants investigation because the neurochemical basis of upper airway motor dysfunction (e.g. obstructive sleep apnea) remains poorly characterized.

The role of dopamine in directly modulating somatic motoneuron excitability and hence muscle tone is unknown. We investigated whether dopamine influences the trigeminal motor pool (MoV) that innervates the masseter and tensor palatini muscles, both of which function to maintain upper airway patency. We hypothesized that dopamine facilitates motor outflow at the MoV. We focally applied apomorphine (nonspecific dopamine receptor agonist) at the MoV in anaesthetized rats. We also applied receptor-specific agonists and antagonists to determine the receptor subtype mediating dopaminergic mechanisms of action. We demonstrated that dopaminergic transmission at the MoV potently increased motor outflow via the D1-like receptor and facilitated masseter and tensor palatini muscle tone. It is unknown whether endogenous dopamine release on to airway motoneurons influences their activity to regulate muscle tone in natural sleep-wake behaviours. This issue warrants investigation because the neurochemical basis of upper airway motor dysfunction (e.g. obstructive sleep apnea) remains poorly characterized.

The astrophysical data of the last two decades have allowed cosmologists to conclude that the present Universe is accelerating. The research carried out to find the origin of this phenomenon has led to the creation of a vast number of dark energy and modified gravity theories, of which the simplest is the ˄CDM model. The latter is, however, plagued with very difficult problems awaiting a solution. The work here presented seeks to contribute to the discussion of the possible explanation for the Cosmos' acceleration and other important questions in modern cosmology using the newest astrophysical observations available. This thesis starts by exploring a dark energy model dubbed thawing quintessence which is characterised by allowing a non constant ratio of pressure to density for dark energy that is however still close to -1 for most of the cosmological evolution, shifting away from this value when the domination of the radiation and matter components fades away. The findings are the most up-to-date constraints for which this model gives a viable theory for dark energy, including a bound on the equation of state at present of w < -0:88. This exact approach was contrasted with the use of an approximate equation-of-state parametrisation for thawing theories. The analysis also includes different parametrisation choices, and comments on the accuracy of the constraints imposed by CMB anisotropies alone. Next, the cosmology of hybrid metric-Palatini gravity is presented. This is a type of Modified Gravity theory in which the Lagrangian density for the gravitational action is a function of the Ricci scalars of both the connection and the metric. The background evolution of two models of this kind is examined explicitly showing the recovery of standard General Relativity at late times. The maximum deviation from the gravitational constant G at early times is constrained using a combination of geometrical data, finding it to be around 1%. A designer scenario, also introduced under the hybrid metric-Palatini formulation, is then used to explore to what extent early modifications of gravity, which become significant after recombination but then decay towards the present, can be constrained by current and future cosmological observations. This model is embedded in the effective field theory description of Horndeski scalar-tensor gravity with an early-time decoupling of the gravitational modification. Applying cosmological data, the constraints on the early-time deviations from General Relativity are obtained. These are dependent on the redshift at which the oscillations in the slip between the gravitational potentials are turned on. For zon = 1000, the deviation from Einstein's theory is ≤ 10-2 with 95% confidence. An explanation of the effect that these divergences have on the CMB power spectrum are discussed, as well as the effect that future 21 cm survey data will have on this study. The last part of this work is a move towards inflation, the early epoch of accelerated expansion undergone by the Universe. Here a parametrisation of the acceleration trajectory is investigated with the aim of measuring the rolling of the inflaton corresponding to the value of the tensor-to-scalar ratio r to be compared with future observations. Considering five ln ε amplitudes and 14 e-foldings, it was found that the posterior distribution of (r,∆Φ) is in very good agreement with Lyth's bound. The analysis included a histogram depiction of the latter result, from which later a minimum constraint on ∆ϕ for each of the bins was found. These outcomes constitute the intermediate step of this project which will be made more accurate by extending it to ~ 50 e-folds, a larger set of cosmological parameters and observational bounds that are restrictive on small scales.

京都大学 / 0048 / 新制・論文博士 / 博士(医学) / 乙第13119号 / 論医博第2132号 / 新制||医||1023(附属図書館) / (主査)教授 大森 孝一, 教授 斎藤 通紀, 教授 長船 健二 / 学位規則第4条第2項該当 / Doctor of Medical Science / Kyoto University / DFAM