Física
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Navegando Física por Autor "Alvarenga, Flávio Gimenes"
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- ItemA classificação de Bianchi e a construção de Taub das métricas cosmológicas anisotrópicas(Universidade Federal do Espírito Santo, 2024-07-15) Scardini, Lucas Oliveira; Gonçalves, Sergio Vitorino de Borba ; https://orcid.org/; http://lattes.cnpq.br/; https://orcid.org/; http://lattes.cnpq.br/; Monerat, Germano Amaral; https://orcid.org/; http://lattes.cnpq.br/; Alvarenga, Flávio Gimenes; https://orcid.org/; http://lattes.cnpq.br/; Spalenza, Wesley; https://orcid.org/; http://lattes.cnpq.br/The study of the cosmos is of utmost importance for understanding the origin of the Universe. One of the foundations in these studies is the metric used, which is commonly homogeneous and isotropic. However, there are works that utilize anisotropic or inhomogeneous metrics. Anisotropic metrics have been divided into different types by the work of Abraham Taub, who based his classification on Luigi Bianchi’s classification of anisotropic manifolds. This dissertation has two objectives: the first is to construct anisotropic metrics starting with a simple review of general relativity. The second is to demonstrate the importance of studying models that do not adhere to the cosmological principle
- ItemA Quantização da Gravitação em 3D com Constante Cosmológica Positiva(Universidade Federal do Espírito Santo, 2012-07-31) Almaraz, Zui Agustin Oporto; Constantinidis, Clisthenis Ponce; Piguet, Olivier; Vanzella, Daniel Augusto Turolla; Ribeiro, Maria Cristina Batoni Abdalla; Alvarenga, Flávio Gimenes; Gomes, Jose Francisco; Gonçalves, Sergio Vitorino de BorbaIt was shown by Bonzom and Livine that 2+1 gravity with cosmological constant contains an ambiguity that depends on a Barbero–Immirzi-like parameter ? known from 4D gravity. Based on this fact, we showed that, for the ? > 0 case, the Lorentzian theory can be partially reduced, thanks to a suitable gauge fixing, to a Chern–Simons theory with compact gauge group SU(2). Then we revised already known loop quantization of Chern–Simons theory for the case of a space with the topology of a cylinder. Finally we construct a quantum observable which, despite having a not trivial spectrum at the quantum level, it corresponds to a classical quantity identically null.
- ItemBuracos negros fantasmas.(Universidade Federal do Espírito Santo, 2010-04-23) Rodrigues, Manuel Eleuterio; Fabris, Júlio César; Alvarenga, Flávio Gimenes; Mello, Eugênio Ramos Bezerra de; Piguet, Olivier; Sotomayor, Patrício Anibal LetelierWe obtain the general solution of the Einstein-(anti) Maxwell-(anti) Dilaton (EMD)theory for a static, spherically symmetric spacetime in four dimensions. In the phantom(anti) cases, we obtain new solutions with non-degenerate horizon and make the analysis oftheir causal structures. The causal structures of some solutions are exotics, some of themcan not be described in two-dimensional usual Penrose diagrams. We obtain also, usingthe method of Sigma model, new stationary solutions with axial symmetry, for Einstein-anti-Maxwell-Dilaton (E ¯MD) and Einstein-anti-Maxwell-Dilaton-Axion (E ¯MDA) theory.We analyse the causal structure of these new solutions.
- ItemConfrontando cosmologias newtoniana e neo-newtoniana através do processo de formação de estruturas(Universidade Federal do Espírito Santo, 2007-09-21) Velten, Hermano Endlich Schneider; Alvarenga, Flávio Gimenes; Gonçalves, Sérgio Vitorino de Borba; Silva, Saulo Carneiro de SouzaIf we utilize the hidrodynamical equations in the study of the Universe we obtain a New-tonian cosmology. However, if we consider the effects of the inercial pressure and thedistinction between gravitacional mass and inercial mass it is possible to obtain a newset of hidrodynamical equations that we call neo-Newtoniancosmology. In this work westudy the aplicabillity of these two approach in structure formation theory throught amodel constituited by baryonic matter and Chaplygin gas. Weconfront the theoreticalpower spectrum of Newtonian cosmology and neo-Newtonian Cosmology with the 2dF-GRS observational data. The purpose of this analysis is to obtain the advantage of eachapproach. Moreover, we search the origin of the oscillations and divergences observed inthe Chaplygin gas power spectrum.
- ItemModelo acústico análogo ao buraco negro de Schwarzschild(Universidade Federal do Espírito Santo, 2010-07-29) Toniato, Júnior Diniz; Gonçalves, Sérgio Vitorino de Borba; Monerat, Germano Amaral; Constantinidis, Clisthenis Ponce; Alvarenga, Flávio GimenesThere isn t experimental evidences that can validate the results of black holes termodynamics. This because the radiation emitted by the black hole, predicted by theory, it is almost impossible to be detected due to its low value of magnitude. In the search for clues that could validate the existence of this radiation, the study of analog models to those objetcs has grown considerably in recent decades. They allow the idealization of experiments in labs that would be extremely complicate to be done directly with the gravitational systems. A fluid in moviment can act on the sound the same way that curved space-time can influence on light trajectory in the general relativity. So, one can describe the propagation these sound waves through an effective metric, under wich they will follow null geodesics. This thesis makes a review of these studies focusing in an analogy to Schwarzschild black hole using an acoustic system, showing its advantages and limitations when applied in the study of Hawking s theory
- ItemO Modelo Cosmológico de Kantowski-Sachs.(Universidade Federal do Espírito Santo, 2021-02-23) Silva, Breno Barreto da; Goncalves, Sergio Vitorino de Borba; https://orcid.org/0000000285709750; http://lattes.cnpq.br/4992784379693871; https://orcid.org/0000000173460129; http://lattes.cnpq.br/8497753547288933; Alvarenga, Flávio Gimenes; https://orcid.org/0000-0002-7579-9561; http://lattes.cnpq.br/7169430092692431; Monerat, Germano Amaral; https://orcid.org/0000-0003-2536-1171; http://lattes.cnpq.br/5031014907752547This work seeks to solve Einstein’s equations for the Kantowski-Sachs metric in a environment containing barotropic fluid coupled to a scalar field and using a relationship between the scale factors of that metric. To achieve this goal, it was necessary to study and address the RobertsonWalker metric, the Einstein-Hilbert action, the Einstein equations, the various moment-energy tensors and the Friedmann equations. We also studied the following fluids: dust, stiff matter, radiation, cosmic strings and vacuum, and their respective equations of state. And finally, we analyze the calculations of the Kantowski-Sachs article for dust and the Adhav article that solves Einstein’s equations for stiff matter with the Kantowski-Sachs metric having a relationship between the scale factors.
- ItemPadrões de difração de elétrons com e sem efeito de fase Aharonov-Bohm e a divergência em sua forma assintótica.(Universidade Federal do Espírito Santo, 2019-05-30) Favarato, Cássio Cecato; Lima, Denise Assafrão; Gonçalves, Sérgio Vitorino de Borba; Mota, Vinícius Cândido; Alvarenga, Flávio Gimenes; Scopel, Wanderlã Luis; Rojas Leyva, Moises PorfirioIt is common during undergraduate courses to study the phenomenon of diffraction of electromagnetic waves by single and double slit systems via scalar diffraction theory and the Kirchoff integral. Alternatively to this, in this thesis, we analyzed the electron diffraction and interference patterns, via Feynman path integrals. For this, we start from the conceptual model, as originally proposed by RPFeynman in Quantum Mechanics and Path Integrals but which, over time, has been treated more rigorously by other authors, and with greater sophistication and clarity by M.Beau in Feynman path integral approach to electron diffraction for one and two slits: analytical results. At first, we preserve all the analysis given by this author to the problem, with some notes about probable misconceptions and construct the free propagators and wave functions for each stage of the movement for the different systems studied. H. Yabuki, in Feynman Path Integrals in the Young Double-Slit Experiment, makes it clear that in the employed representation, despite being able to extract information about the most diverse possible trajectories, the probabilistic weight of events as loops are relatively negligible, validating the superposition principle as the sum of the emerging wave functions of each slot region. From this we obtain the expression that takes the electronic distributions on the screen. By means of the variation of parameters, such as the geometric and Fresnel number contained in it, the different regimes of the optics appear: Fraunhouffer, Intermediate and Fresnel. Therefore, it was realized that these regimes could be recovered through special conditions conferred the asymptotic forms of Fresnel functions. We extend these arguments to the expression that leads to the electronic distribution with Aharonov-Bohm (AB) phase effect. Throughout a succession of approximations, we reached an expression with physical meaning and the existence of other mathematical expressions that carried divergences in their domains, corroborating the inexistence of an analogous expression to that typical of the regime of Fraunhoffer with mixed phase, that manifests the asymmetries AB. Finally, we demonstrate the emergence of the Berry phase and its relation to the AB phase.
- ItemProbabilidade de tunelamento quântico para o surgimento de um universo clássico preenchido com gás de Chaplygin e poeira(Universidade Federal do Espírito Santo, 2023-03-14) Rocha, Nathália Mattos Novaes da; Goncalves, Sergio Vitorino de Borba; https://orcid.org/0000000285709750; http://lattes.cnpq.br/4992784379693871; https://orcid.org/0000000345816364; http://lattes.cnpq.br/5376461651668363; Ribeiro, Andre Luis Batista; https://orcid.org/0000-0002-3813-2565; http://lattes.cnpq.br/3417734567782570; Alvarenga, Flávio Gimenes; http://lattes.cnpq.br/7169430092692431; Silva, Eduardo Vasquez Corrêa; https://orcid.org/0000-0003-3866-8105; http://lattes.cnpq.br/0541169610474136; Constantinidis, Clisthenis Ponce; http://lattes.cnpq.br/1328163673123152; Oliveira Neto, Gil deThe present work aims to analyze the quantum dynamics contained in the Planck era of the Universe, its emergence mechanism for the inflationary phase and its classical dynamics in a homogeneous and isotropic model, composed of a perfect fluid in the form of dust and a Chaplygin gas. The analysis was carried out through probabilistic calculations of quantum tunneling of a numerical model quantized by the Crank-Nicolson method, whose calculations were performed in terms of the model parameters. The results show a greater susceptibility for the classical emergence of a Universe filled with dust and Chaplygin gas, when compared to results found in the literature for a model in which the Universe is filled with Chaplygin gas and radiation.
- ItemQuantização de Laços no Modelo BF em 2+1 dimensões(Universidade Federal do Espírito Santo, 2010-03-09) Mendonça, Diego Cézar Monteiro de; Constantinidis, Clisthenis Ponce; Piguet, Olivier; Alvarenga, Flávio Gimenes; Helayël Neto, José; Piguet, Olivier; Constantinidis, Clisthenis PonceThe goal of this paper is to serve as an introductory text to the following topics: canonical quantization, loop quantization, and the BF model. To this end, we develop appropriate mathematical tools for treating a topological gauge theory of the general Yang-Mills type to formulate a covariant action and study its symmetries via the canonical Dirac quantization method, also known as the Hamiltonian bound method. This method is developed extensively, although it retains its introductory character, for the case of the 2+1 dimensional BF model, which we then quantize via bonds and find identifications of this whole process with the theory of general relativity expressed as a gauge theory. Finally, we will see how the quantum mechanics of these gauge theories develops by describing the basis for our state functions which is called the spin network, as well as the dynamics of these loop quantized theories which is described by the formalism of spin foams and also the calculation of some observables associated with our states.