Cosmological Models
Mostrando 13-24 de 32 artigos, teses e dissertações.
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13. Cosmological models of universe with variable deceleration parameter in Lyra's manifold
FRW models of the universe have been studied in the cosmological theory based on Lyra's manifold. A new class of exact solutions has been obtained by considering a time dependent displacement field for variable deceleration parameter from which three models of the universe are derived (i) exponential (ii) polynomial and (iii) sinusoidal form respectively. Th
Brazilian Journal of Physics. Publicado em: 2006-12
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14. Stability in a class of quartessence models
Quartessence cosmological models with exponential and logarithmic equation of state are investigated using dynamical systems methods. We focus our analysis on the stability of these models.
Brazilian Journal of Physics. Publicado em: 2006-09
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15. Criação da matéria em cosmologias com velocidade da luz variável e eletrônico não-linear
In this work we obtain the cosmological solutions and investigate the thermodynamics of matter creation in two diferent contexts. In the first we propose a cosmological model with a time varying speed of light c. We consider two diferent time dependence of c for a at Friedmann-Robertson- Walker (FRW) universe. We write the energy conservation law arising fro
Publicado em: 2006
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16. Cosmologia na teoria de Visser / Cosmology from the Visser s theory
The advent of observational cosmology has led us to conclude that only 4% of whole Universe is composed by known matter (baryons). On the other hand 23% comes from a kind of non barionic dark matter. Moreover the cosmic dynamics is almost fully dominated by the so called dark energy (usually considered a kind of fluid), which corresponds to 73% of the energy
Publicado em: 2006
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17. On the non-integrability of a class of hamiltonian cosmological models
The method of Morales and Ramis determines whether a given Hamiltonian system is non-integrable. We apply this method to Friedmann Robertson Walker models with a self-interacting scalar field and cosmological constant. It is shown that, with the exception of a set of measure zero, these models are non-integrable. Our results complement those of Helmi and Vuc
Brazilian Journal of Physics. Publicado em: 2005-12
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18. Toy models unifying dark energy and dark matter
It is very common to find numerical studies of dark energy and dark matter. Among these, one can find the interesting proposal of unifying dark matter and dark energy with the use of a single component with an 'exotic' equation of state. However, there is a certain shortage of analyses involving exact analytic models following this proposal. Therefore, here
Brazilian Journal of Physics. Publicado em: 2005-12
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19. Phase space solutions in scalar-tensor cosmological models
An analysis of the solutions for the field equations of generalized scalar-tensor theories of gravitation is performed through the study of the geometry of the phase space and the stability of the solutions, with special interest in the Brans-Dicke model. Particularly, we believe to be possible to find suitable forms of the Brans-Dicke parameter w and potent
Brazilian Journal of Physics. Publicado em: 2005-12
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20. Geometrical generation of cosmic magnetic fields within standard electromagnetism
We study the evolution of cosmological magnetic fields in FRW models with curved spatial sections and outline a geometrical mechanism for their superadiabatic amplification on large scales. The mechanism operates within standard electromagnetic theory and applies to FRW universes with open spatial sections. We discuss the general relativistic nature of the e
Brazilian Journal of Physics. Publicado em: 2005-12
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21. Nonlinear resonance in bouncing universes
The dynamics of closed LFRW universes with a massive inflaton field is examined where Friedmann equations are corrected by the introduction of a potential term arising from quantum gravity corrections to cosmological scenarios near the singularity. This extra term implements nonsingular bounces in the early evolution of the universe. For certain windows in t
Brazilian Journal of Physics. Publicado em: 2005-12
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22. Some results on the evolution of primordial black holes
We briefly review some recent results related to thermodynamics of semiclassical black holes applied to their primordial formation. Issues on the existence of an influx of ambient particles onto the PBHs, which may help grow them, are addressed. We revisit the integrated flux from evaporated PBHs contributing to the present backgrounds and show that there pr
Brazilian Journal of Physics. Publicado em: 2005-12
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23. Remarks on some vacuum solutions of scalar-tensor cosmological models
We present a class of exact vacuum solutions corresponding to de Sitter and warm inflation models in the framework of scalar-tensor cosmologies. We show that in both cases the field equations reduce to planar dynamical systems with constraints. Then, we carry out a qualitative analysis of the models by examining the phase diagrams of the solutions near the e
Brazilian Journal of Physics. Publicado em: 2004-06
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24. Classification of energy momentum tensors in n > 5 dimensional space-times: a review
Recent developments in string theory suggest that there might exist extra spatial dimensions, which are not small nor compact. The framework of a great number of brane cosmological models is that in which the matter fields are confined on a brane-world embedded in five dimensions (the bulk). Motivated by this we review the main results on the algebraic class
Brazilian Journal of Physics. Publicado em: 2004-06