| Resumo: |
In this dissertation, we study the Horndeski theories, a form of Modified Gravity (MG), alternative to General Relativity (GR), that has the purpose of explaining the recent accelerated expansion of the universe. We forecast measurements of cosmological parameters from the 21-cm signal, planned to be made soon by BINGO radiotelescope. Such maps were built from theoretical angular power spectrum, computed taking into account the WMAP5 cosmology, and defining the bias and the neutral hydrogen energy density from N-body simulations. Initially, we placed constraints on a sub-class of Horndeski with luminally propagating gravitational waves (GWs). From the 21-cm signal, we did not find a significant departure from GR for both i parameterizations. Considering the CMB data, the MG parameters are reduced to 10^-1 order, and we recovered the Hubble constant and the cold dark matter energy density, measured by WMAP5 experiment. The parameter measurements with the combined data (BINGO+CMB) provide the best estimates. Finally, for a more general class of Horndeski in which the tensor speed excess is allowed to vary, the dataset BINGO+CMB favour sub-luminal propagating GWs, as predicted theoretically. |
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