New avenues for investigating the Large-Scale Structure of our Universe

This thesis deals with characterizing the behavior of dark components (Dark energy and Dark mat- ter relative to the baryons) in cosmology by following new avenues for investigating the Large-Scale Structure (LSS). Near future surveys would probe the structure formation with remarkable precision in order to constrain cosmological parameters and deepen our understanding of the nature of these components. In the first part, with a general phenomenological view on the dark energy component of the Universe, we study the behavior of a perturbed Early dark Energy (EDE) model as an additional energy component in the early Universe involving the sound speed and anisotropic stress. We investigate the impact of EDE on cosmological observables such as the Cosmic Microwave Background (CMB) angular power spectrum as well as the linear matter power spectra. We mainly focus on the quantitative exploration of an extended parameter space including the mass of neutrinos and tensor to scalar ratio in the light of recently available data sets. As we will show, the constraints on the EDE parameters are remarkably stable even when Σmν, and r parameters are varied. In the second part, we concentrate on the physics of the matter components of the Universe by a direct calculation of the coupling of baryons to the Cold Dark Matter (CDM) components. We perform 2-fluid gravity-only N-body simulations and assess the impact of relative baryon-CDM density perturbations in dark matter halo distribution which is usually neglected in LSS studies. Specifically, we focus on the baryon fraction in halos as a function of mass and large-scale baryon- CDM perturbations, which allows us to study the details of the nontrivial numerical setup required for such simulations as well. By quantifying the impact of such perturbations on halo-halo power spectra we found this effect can be degenerate with the one of massive neutrinos in near future and operating LSS surveys. Finally, we investigate the statistics of various promising LSS probes in configuration space in gravity-only 2-fluid N-body simulations mentioned above. This allows us to study the impact of baryon-CDM perturbations on these statistics. Particularly, we focus on the statistics of the cosmic voids, as well as on the matter 2-point correlation function and Baryon Acoustic Oscillations (BAO) peak as a robust cosmological standard ruler. We find the impact of 1 − 2% level at maximum on the void size function which is more prominent at higher redshifts, while the void density profile and void bias are roughly unaffected. Our results confirm the impact of baryon-CDM perturbations on cosmological constraints from the BAO feature in current and future galaxy surveys should be negligible at low redshift.