Resumo:
Contemporary cosmology is largely grounded in the standard ΛCDM model, based on
the Friedmann–Lemaître–Robertson–Walker (FLRW) metric and on the Cosmological
Principle, which assumes large-scale homogeneity and isotropy. This model has been
highly successful in describing cosmic expansion, the anisotropies of the cosmic microwave
background, and the formation of large-scale structures, although its formulation depends
on the introduction of components that are not yet fully understood, such as dark matter
and dark energy, in addition to assuming global symmetries that contrast with the observed
inhomogeneities, such as clusters, filaments, and cosmic voids. In light of these limitations,
alternative models have been developed that relax the conditions of the Cosmological
Principle, such as the Lemaître–Tolman–Bondi (LTB), Szekeres, and Locally Rotationally
Symmetric (LRS) models, allowing for more general matter distributions. More recently,
intrinsically symmetric models have emerged, which preserve internal symmetries without
requiring global homogeneity, providing a more flexible framework to investigate the effects
of inhomogeneities on cosmological parameters. In this work, we develop the linear scalar
perturbation framework for intrinsically symmetric models, analyzing how the presence
of spatial gradients in the geometric background alters the evolution equations of the
fluctuations. Our goal is to establish the theoretical basis to confront these models with
the ΛCDM paradigm and investigate potential observational signatures of inhomogeneity.
