Anisotropias da radiação cósmica de fundo e vínculos em modelos com decaimento do vácuo

Many astronomical observations in the last few years are strongly suggesting that the current Universe is spatially flat and dominated by an exotic form of energy. This unknown energy density accelerates the universe expansion and corresponds to around 70% of its total density being usually called Dark Energy or Quintessence. One of the candidates to dark energy is the so-called cosmological constant (Λ) which is usually interpreted as the vacuum energy density. However, in order to remove the discrepancy between the expected and observed values for the vacuum energy density some current models assume that the vacuum energy is continuously decaying due to its possible coupling with the others matter fields existing in the Cosmos. In this dissertation, starting from concepts and basis of General Relativity Theory, we study the Cosmic Microwave Background Radiation with emphasis on the anisotropies or temperature fluctuations which are one of the oldest relic of the observed Universe. The anisotropies are deduced by integrating the Boltzmann equation in order to explain qualitatively the generation and c1assification of the fluctuations. In the following we construct explicitly the angular power spectrum of anisotropies for cosmologies with cosmological constant (ΛCDM) and a decaying vacuum energy density (Λ(t)CDM). Finally, with basis on the quadrupole moment measured by the WMAP experiment, we estimate the decaying rates of the vacuum energy density in matter and in radiation for a smoothly and non-smoothly decaying vacuum

Teorias f(R) de gravidade na formulação de Palatini

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 Gödel model being the best known example of such a solution. Here we show that every perfect-fluid Gödel-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 Gödel geometry, demonstrating, therefore, that these theories present causal anomalies in the form of closed time-like curves. This result extends a theorem on Gödel-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 Gödel-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 Gödel 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 Gödel-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 Gödeltype solution with no violation of causality. Finally, we show that by combining a perfect fluid plus a scalar field as sources of Gödel-type geometries, we obtain both solutions in the form of closed time-like curves, as well as solutions with no violation of causality

Fatores que influenciam a predisposição dos usuários em aderir a uma política de segurança da informação

The information constitutes one of the most valuable strategic assets for the organization. However, the organizational environment in which it is inserted is very complex and heterogeneous, making emerging issues relevant to the Governance of information technology (IT) and Information Security. Academic Studies and market surveys indicate that the origin of most accidents with the information assets is the behavior of people organization itself rather than external attacks. Taking as a basis the promotion of a culture of safety among users and ensuring the protection of information in their properties of confidentiality, integrity and availability, organizations must establish its Information Security Policy (PSI). This policy is to formalise the guidelines in relation to the security of corporate information resources, in order to avoid that the asset vulnerabilities are exploited by threats and can bring negative consequences to the business. But, for the PSI being effective, it is required that the user have readiness to accept and follow the procedures and safety standards. In the light of this context, the present study aims to investigate what are the motivators extrinsic and intrinsic that affect the willingness of the user to be in accordance with the organization's security policies. The theoretical framework addresses issues related to IT Governance, Information Security, Theory of deterrence, Motivation and Behavior Pro-social. It was created a theoretical model based on the studies of Herath and Rao (2009) and D'Arcy, Hovav and Galletta (2009) that are based on General Deterrence Theory and propose the following influencing factors in compliance with the Policy: Severity of Punishment, Certainty of Detection, Peer Behaviour, Normative Beliefs, Perceived Effectiveness and Moral Commitment. The research used a quantitative approach, descriptive. The data were collected through a questionnaire with 18 variables with a Likert scale of five points representing the influencing factors proposed by the theory. The sample was composed of 391 students entering the courses from the Center for Applied Social Sciences of the Universidade Federal do Rio Grande do Norte. For the data analysis, were adopted the techniques of Exploratory Factor Analysis, Analysis of Cluster hierarchical and nonhierarchical, Logistic Regression and Multiple Linear Regression. As main results, it is noteworthy that the factor severity of punishment is what contributes the most to the theoretical model and also influences the division of the sample between users more predisposed and less prone. As practical implication, the research model applied allows organizations to provide users less prone and, with them, to carry out actions of awareness and training directed and write Security Policies more effective.