DEFIS - Departamento de Física
URI Permanente desta comunidade
Navegar
Navegando DEFIS - Departamento de Física por Autor "Algoner Jorge, William Celestino"
Agora exibindo 1 - 2 de 2
Resultados por página
Opções de Ordenação
Item Matter growth in extended ΛCDM cosmology.(2019) Wilhelm, Zimdahl Winfried Ernst; Velten, Hermano Endlich Schneider; Algoner Jorge, William CelestinoOn the basis of a previously established scalar–tensor extension of the ΛCDM model, we develop an effective fluid approach for the matter growth function. This extended ΛCDM (henceforth eΦΛCDM) cosmology takes into account deviations from the Standard Model both via a modified background expansion and by the inclusion of geometric anisotropic stresses as well as of perturbations of the geometric dark-energy equivalent. The background dynamics is governed by an explicit analytic expression for the Hubble rate in which modifications of the Standard Model are given in terms of a single constant parameter [W. C. Algoner, H. E. S. Velten and W. Zimdahl, J. Cosmol. Astropart. Phys. 1611 (2016) 034]. To close the system of fluid-dynamical perturbation equations, we introduce two phenomenological parameters through which the anisotropic stress is related both to the total energy density perturbation of the cosmic substratum and to relative perturbations in the effective two-component system. We quantify the impact of deviations from the standard background, of anisotropic stresses and of nonvanishing perturbations of the effective dark-energy component on the matter growth rate function fσ8 and confront the results with recent redshift-space distortion (RSD) measurements.Item Matter growth in imperfect fluid cosmology.(2019) Wilhelm, Zimdahl Winfried Ernst; Velten, Hermano Endlich Schneider; Algoner Jorge, William CelestinoExtensions of Einstein’s General Relativity (GR) can formally be given a GR structure in which additional geometric degrees of freedom are mapped on an effective energy-momentum tensor. The corresponding effective cosmic medium can then be modeled as an imperfect fluid within GR. The imperfect fluid structure allows us to include, on a phenomenological basis, anisotropic stresses and energy fluxes which are considered as potential signatures for deviations from the cosmological standard Λ-cold-dark-matter (ΛCDM) model. As an example, we consider the dynamics of a scalar-tensor extension of the standard model, the eΦΛCDM model. We constrain the magnitudes of anisotropic pressure and energy flux with the help of redshift-space distortion (RSD) data for the matter growth function f σ8.