Neutrinos and voids in modern cosmology

This thesis deals with the study of the large scale structure in the nonlinear regime. In particular, it focuses on two main topics: the impact of massive neutrinos on the cosmic web and the modeling of void profiles and void bias. Neutrinos are known to be massive particles and thus to participate to the matter content of the Universe and to its evolution. In this era of precision cosmology, the analysis of observational datasets must account for neutrinos, both because cosmology can put strong constraints on the sum of their masses, and because ignoring them can bias the estimation of other cosmological parameters. Having this in mind, we provide a theoretical model to describe the nonlinear matter power spectrum in massive neutrino cosmologies. This model is obtained by generalizing the already existing halo model, to account for the presence of massive neutrinos. Then, we also discuss the clustering of galaxies in the same framework and provide a comparison with N-body simulations. A promising environment where to study neutrinos is represented by cosmic voids. We perform a numerical analysis of statistical properties of voids, identified both in ΛCDM and massive neutrino cosmologies. The aim of this project is to understand how neutrinos change the void properties and which of them are more sensitive to their presence. This is the starting point for thinking about constraining neutrino masses using cosmic voids. Voids are very interesting objects, that have been studied much less than halos and clusters. We present here a model for describing the void density profile. In particular, we present different models describing the abundance and spatial distribution of both halos and voids in the Lagrangian field, and explain how they can be applied to compute density profiles. Then, we evolve these Lagrangian profiles to the Eulerian space, where actual measurements are performed. We discuss the evolution described by the spherical model and the Zel’dovich approximations. Since the density profile around tracers is the cross-correlation between the tracers and the matter field, this quantity is sensitive to the bias of tracers with respect to the matter field. We discuss the void linear bias in Lagrangian and Eulerian space, and how it differs from the linear bias of halos.