Doutorado em Física

URI Permanente para esta coleção

http://repositorio.ufes.br/handle/10/17493

Nível: Doutorado
Ano de início: 2003
Conceito atual na CAPES: 4
Ato normativo: Parecer CES/CNE nº 487/2018, homologado pela Port. MEC 609, publicado no DOU em 18/03/2019.
Periodicidade de seleção: Semestral
Área(s) de concentração: Física
Url do curso: https://fisica.ufes.br/pt-br/pos-graduacao/PPGFis/detalhes-do-curso?id=1509

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Navegando Doutorado em Física por Autor "Alvarenga, Flavio Gimenes"

Agora exibindo 1 - 4 de 4
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    Criação de partículas em modelos cosmológicos
    (Universidade Federal do Espírito Santo, 2010-09-24) Houndjo, Stéphane Jonas Mahouton; Fabris, Júlio César; Batista, Antonio Brasil; Alvarenga, Flavio Gimenes; Chapiro, Ilia; Pinto Neto, Nelson; Piguet, Olivier; Silva, Saulo Carneiro de Souza
    We investigate particle production in an expanding universe dominated by a perfect fluid with the equation of state p = a?. The particle production rate, using the Bogoliubov coefficients, is determined exactly for any value of a in the case of a flat universe. When the strong enegy condition is satisfied, the particle production rate decreases with time; the opposite occurs when the strong energy condition is violated. In the phantom case, the particle production rate diverges at finite time for each mode represented by a wavenumber k. In a first step, in order to compute the energy density associated with the produced particles, we use a cut-off in the Planck scale and find that it tends to zero as the big rip is approached. We conclude that quantum effects due to particle creation are not able to prevent the big rip. In the second step, in order to perform a deep analysis of the quantum effects, we use the n-wave regularization technique for calculating the quantum energy density and find that it becomes the dominant component of the universe near the big rip. We conclude in this case that quantum effects can prevent the occurrence of the big rip. We also investigate the effects of quantum particle production on a classical sudden singularity occurring at finite time in a Friedmann universe. We use an exact solution to describe an initially radiation-dominated universe that evolves into a sudden singularity at finite time. We calculate the density of the created particles exactly and find that it is generally much smaller than the classical background density and pressure which produce the sudden singularity. We conclude that, in the example studied, quantum particle production does not avoid nor modify of the sudden future singularity
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    Modelos cosmológicos quânticos com fluido perfeito
    (Universidade Federal do Espírito Santo, 2018-10-25) Fracalossi, Raphael; Alvarenga, Flavio Gimenes; Gonçalves, Sergio Vitorino de Borba; Constantinidis, Clisthenis Ponce; Lourenço, José André; Lemos, Nivaldo Agostinho
    In this work, quantum cosmological models with perfect fluid are studied according to the canonical approach of Quantum Cosmology. The material content of the Universe is described by Schutz’s formalism, which is discussed in detail and used as a tool in order to solve the problem of absence of a time variable in theory. In this context, two models are constructed containing a stiff matter fluid. In the first one, a two-fluid model, stiff matter and radiation in a homogeneous and isotropic Universe described by FLRW metric. It is observed that the initial singularity in the classic model is apparently removed in the quantum approach. In the second, an anisotropic quantum cosmological model described by Kantowski-Sachs metric is discussed. As a result, it is found that although the Hamiltonian operator associated with the model is symmetric, the norm of wave function of Universe is time-dependent, implying loss of unitarity, reinforcing the existence of a pathology already verified in quantum cosmological model described by Bianchi I anisotropic metric.
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    Perturbações cosmológicas de origens quântica e clássica : oscilações no espectro de potência e o condensado de Bose-Einstein
    (Universidade Federal do Espírito Santo, 2014-09-24) Freitas, Rodolfo Camargo de; Gonçalves, Sergio Vitorino de Borba; Constantinidis, Clisthenis Ponce; Alvarenga, Flavio Gimenes; Martins, Gabriel Luchini; Monerat, Germano Amaral; Piattella, Oliver Fabio
    The relativistic perturbations of quantum origin are the “seeds” that evolved into the large scale structures throughout classical gravitational instabilities. We study the gauge invariant formalism for the cosmological perturbations and we apply into a two fields model, where one of them suffers a gain of mass, that causes a sharp turn in the fields trajectory, resulting in oscillations of the primordial power spectrum with amplitudes bounded by the observational data. We also study the structure formation within a dark matter model, where dark matter particles are described by a Bose-Einstein condensate
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    Quantização do modelo de Jackiw-Teitelboim no gauge temporal via o formalismo de laços
    (Universidade Federal do Espírito Santo, 2009-06-30) Lourenço, José André; Constantinidis, Clisthenis Ponce; Piguet, Olivier; Franco, Daniel Heber Theodoro; Alvarenga, Flavio Gimenes; Sotkov, Galen Mihaylov; Pinto Neto, Nelson; Constantinidis, Clisthenis Ponce; Piguet, Olivier
    In this work we study the Jackiw-Teitelboim model (JT model), as a model that has the structure of a topological theory of the BF type. In two dimensional space-time, gravitation can be seen as a gauge theory characterized by the Poincaré group ISO(1, 1). As this group, doesn't admit an invariant and nondegenerate quadratic form, the JT model is based on the (Anti)- de Sitter group (A)dS , the group SO(2, 1), which contains the Lorentz group as a subgroup and corresponds to a gravitation theory with a cosmological constant. We see then, that the (A)dS group, taken as a gauge group, contains naturally the di eomorphism symmetry. In this line we investigate the canonical formulation of the JT model in order to quantize it through the formalism of loop quantum gravity (LQG). Following Dirac's program of canonical quantization applied to the loop formalism, we obtain a quantum con guration space starting from the Bohr compacti cation of the real line, we build the respective kinematic Hilbert space and we de ne in a consistent way the volume operator. Finally, we treat the dynamics of the model at the quantum level through the implementation of the constraints originating from the classical theory of the JT model in the temporal gauge in an appropriate Hilbert space.