Ondas gravitacionais em modelos cosmológicos: isotrópicos e anisotrópicos
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Data
2025-04-22
Autores
Viana, Luar Samir Oliveira
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Universidade Federal do Espírito Santo
Resumo
Gravitational waves of cosmological origin are currently one of the most promising channels for probing the early universe. While homogeneous and isotropic cosmological models are extensively employed to describe the gravitational backgrounds through which gravitational radiation propagates, anisotropic models can account for certain phenomena not predicted by the standard model, such as specific anomalies observed in the cosmic microwave background (CMB). Therefore, in this dissertation, we analyze the theoretical formulation of gravitational waves within both the isotropic FLRW model and the anisotropic Bianchi type I model. To this end, we initially adopt the gauge-dependent classical approach of cosmological perturbation theory. The issue of gauge fixing is given special attention, and we find that the commonly used synchronous, transverse, and traceless gauges, which are widely employed in the isotropic case, are no longer mutually compatible in the anisotropic scenario, even though the longitudinal components of gravitational waves have no physical significance, as demonstrated throughout this work. Consequently, the two irreducible, decoupled polarization modes typical of gravitational waves can no longer be obtained solely through a gauge analysis, and the resulting wave equations are coupled. In light of this, we employ the gauge-invariant formalism for a comprehensive physical analysis and interpretation, from which we derive the two polarization modes, for all possible wave vector configuration, and obtain analytical solutions to the wave equations for various particular cases. Ultimately, we believe this work provides a relevant analysis of the gauge issue, given the existing discrepancies in the specialized literature.
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Ondas gravitacionais , Cosmologia , Isotropia