DSpace Collection:
http://repositorio.ufes.br/handle/10/146
2020-11-27T08:57:13ZAn analysis of helium primordial nucleosynthesis with a variable cosmological coupling
http://repositorio.ufes.br/handle/10/757
Title: An analysis of helium primordial nucleosynthesis with a variable cosmological coupling
Authors: Alvarenga, Flávio Gimenes; Fabris, Júlio César; Gonçalves, Sergio Vitorino de Borba; Marinho, Josenilson Ádnei Oliveira
Abstract: The synthesis of helium in the early Universe depends on many input parameters, including the value of the gravitational coupling during the period when the nucleosynthesis takes place. We compute the primordial abundance of helium as function of the gravitational coupling, using a semi-analytical method, in order to track the influence of G in the primordial nucleosynthesis. To be specific, we construct a cosmological model with varying G, using the Brans-Dicke theory. The greater the value of G at nucleosynthesis period, the greater the predicted abundance of helium. Using the observational data for the abundance of primordial helium, constraints for the time variation of G are established.2001-12-01T00:00:00ZAlvarenga, Flávio GimenesFabris, Júlio CésarGonçalves, Sergio Vitorino de BorbaMarinho, Josenilson Ádnei OliveiraThe synthesis of helium in the early Universe depends on many input parameters, including the value of the gravitational coupling during the period when the nucleosynthesis takes place. We compute the primordial abundance of helium as function of the gravitational coupling, using a semi-analytical method, in order to track the influence of G in the primordial nucleosynthesis. To be specific, we construct a cosmological model with varying G, using the Brans-Dicke theory. The greater the value of G at nucleosynthesis period, the greater the predicted abundance of helium. Using the observational data for the abundance of primordial helium, constraints for the time variation of G are established.Gravitational waves : a 100-year tool applied to the dark energy problem
http://repositorio.ufes.br/handle/10/661
Title: Gravitational waves : a 100-year tool applied to the dark energy problem
Authors: Soares-Santos, M.; Gonçalves, Sergio Vitorino de Borba; Fabris, Júlio César; Dal Pino, Elisabete Maria de Gouveia
Abstract: Recent observations from type Ia Supernovae and from cosmic microwave background (CMB) anisotropies have revealed that most of the matter of the Universe interacts in a repulsive manner, composing the so-called dark energy constituent of the Universe. Determining the properties of dark energy is one of the most important tasks of modern cosmology and this is the main motivation for this work. The analysis of cosmic gravitational waves (GW) represents, besides the CMB temperature and polarization anisotropies, an additional approach in the determination of parameters that may constrain the dark energy models and their consistence. In recent work, a generalized Chaplygin gas model was considered in a flat universe and the corresponding spectrum of gravitational waves was obtained. In the present work we have added a massless gas component to that model and the new spectrum has been compared to the previous one. The Chaplygin gas is also used to simulate a L-CDM model by means of a particular combination of parameters so that the Chaplygin gas and the L-CDM models can be easily distinguished in the theoretical scenarios here established. We find that the models are strongly degenerated in the range of frequencies studied. This degeneracy is in part expected since the models must converge to each other when some particular combinations of parameters are considered.2005-12-01T00:00:00ZSoares-Santos, M.Gonçalves, Sergio Vitorino de BorbaFabris, Júlio CésarDal Pino, Elisabete Maria de GouveiaRecent observations from type Ia Supernovae and from cosmic microwave background (CMB) anisotropies have revealed that most of the matter of the Universe interacts in a repulsive manner, composing the so-called dark energy constituent of the Universe. Determining the properties of dark energy is one of the most important tasks of modern cosmology and this is the main motivation for this work. The analysis of cosmic gravitational waves (GW) represents, besides the CMB temperature and polarization anisotropies, an additional approach in the determination of parameters that may constrain the dark energy models and their consistence. In recent work, a generalized Chaplygin gas model was considered in a flat universe and the corresponding spectrum of gravitational waves was obtained. In the present work we have added a massless gas component to that model and the new spectrum has been compared to the previous one. The Chaplygin gas is also used to simulate a L-CDM model by means of a particular combination of parameters so that the Chaplygin gas and the L-CDM models can be easily distinguished in the theoretical scenarios here established. We find that the models are strongly degenerated in the range of frequencies studied. This degeneracy is in part expected since the models must converge to each other when some particular combinations of parameters are considered.MOND virial theorem applied to a galaxy cluster
http://repositorio.ufes.br/handle/10/660
Title: MOND virial theorem applied to a galaxy cluster
Authors: Fabris, Júlio César; Velten, Hermano Endlich Schneider
Abstract: Large values for the mass-to-light ratio (ϒ) in self-gravitating systems is one of the most important evidences of dark matter. We propose a expression for the mass-to-light ratio in spherical systems using MOND. Results for the COMA cluster reveal that a modification of the gravity, as proposed by MOND, can reduce significantly this value.2009-09-01T00:00:00ZFabris, Júlio CésarVelten, Hermano Endlich SchneiderLarge values for the mass-to-light ratio (ϒ) in self-gravitating systems is one of the most important evidences of dark matter. We propose a expression for the mass-to-light ratio in spherical systems using MOND. Results for the COMA cluster reveal that a modification of the gravity, as proposed by MOND, can reduce significantly this value.Amoroso Costa e o primeiro livro brasileiro sobre a relatividade geral
http://repositorio.ufes.br/handle/10/659
Title: Amoroso Costa e o primeiro livro brasileiro sobre a relatividade geral
Authors: Eisenstaedt, Jean; Fabris, Júlio César
Abstract: Em 1922, o físico-matemático brasileiro Amoroso Costa publicou um livro de introdução à Teoria da Relatividade. Este livro, um dos primeiros textos sobre o assunto no mundo, surpreende ainda hoje pela sua limpidez, precisão e concisão. Fazemos uma análise do texto de Amoroso Costa, situando-o no contexto científico mundial e brasileiro.; ABSTRACT In 1922, the Brazilian physicist and mathematician Amoroso Costa published an introduction to the Theory of Relativity. This book, one of the first on the subject in the world, is until now an impressive example of precision, clarity and concision in the treatement of this difficult subject. We present an analysis and evaluation of the text of Amoroso Costa in the scientific context of that period.2004-01-01T00:00:00ZEisenstaedt, JeanFabris, Júlio CésarEm 1922, o físico-matemático brasileiro Amoroso Costa publicou um livro de introdução à Teoria da Relatividade. Este livro, um dos primeiros textos sobre o assunto no mundo, surpreende ainda hoje pela sua limpidez, precisão e concisão. Fazemos uma análise do texto de Amoroso Costa, situando-o no contexto científico mundial e brasileiro.
ABSTRACT In 1922, the Brazilian physicist and mathematician Amoroso Costa published an introduction to the Theory of Relativity. This book, one of the first on the subject in the world, is until now an impressive example of precision, clarity and concision in the treatement of this difficult subject. We present an analysis and evaluation of the text of Amoroso Costa in the scientific context of that period.