Randrianjanahary, Liantsoa Finaritra2024-11-052024-11-052024https://hdl.handle.net/10566/17455We explore the information from HI power spectra (tree-level and one-loop) in redshift space and bispectrum tree-level models. 21-cm emission from neutral hydrogen is a promising tool for probing the matter distribution in the universe post-reionization. The HI signals contain signatures of the primordial universe and the growth of large-scale structure in the universe. These signatures are typically analyzed via the 2-point correlation function or power spectrum. However, adding the information from the 3-point correlation function or bispectrum will be crucial to exploiting next-generation intensity mapping experiments. Upcoming surveys by SKAO and HIRAX will undertake intensive line-intensity observations, complementing galaxy surveys. This study provides new forecasts on cosmological constraints derived from the combined analysis of the 21cm power spectrum and bispectrum. We use Fisher predictions to examine how useful these surveys might be for constraining cosmological parameters, BAO distance functions, growth function, and what they mean for dynamical dark energy and modified gravity. We account for telescope beam effects, instrumental noise, foreground avoidance, the Alcock-Paczynski effect, and theoretical modeling errors in the correlators. The investigation also includes assessments of 21-cm clustering bias up to the second order.enAlcock-PaczynskiMeerKATRelativistic CosmologyDark EnergyNeutral HydrogenThesis