Large-scale structure with massive neutrinos and modified gravity: A simulation-based approach

Abstract

Massive neutrinos and alternative theories of gravity are two seemingly different aspects of cosmological study. On one hand, we have actual particles known to exist, and on the other, a proposed change to the description of gravity. While the presence of massive neutrinos suppresses structure formation on certain scales, modified gravity theories tend to enhance it, resulting in a degenerate effect for some cosmological observables. To properly constrain models of modified gravity, this degeneracy must be considered. This is also true in reverse, when using cosmology to constrain the absolute mass scale of neutrinos, which is yet to be accurately determined. In this thesis, the effects of modified gravity and massive neutrinos are investigated both separately and combined. This is done through the development, use, and analysis of cosmological simulations. The above-mentioned degeneracy is further explored via the analysis of cosmic voids, which are vast underdense regions in the cosmic web. In addition, a pipeline for generating emulators of large-scale structure statistics for universe models beyond the standard one is created using approximate simulation techniques and machine learning. This pipeline, named Sesame, opens the opportunity of studying alternative universe models without the need for large computing resources.