Relativistic effects in the power spectrum of the large scale structure

TL;DR

This paper investigates the impact of relativistic effects and primordial non-Gaussianity on the large-scale structure power spectrum, providing new theoretical expressions and assessing detectability with future surveys.

Contribution

It derives relativistic density power spectrum expressions including non-Gaussianity, and analyzes their detectability and impact on future large-scale structure surveys.

Findings

Relativistic effects can be significant at large scales.

Primordial non-Gaussianity influences the power spectrum and bispectrum.

Relativistic effects may be detectable with Stage-IV surveys.

Abstract

The forthcoming Stage-IV experiments aim to map the large scale structure of the Universe at high precision. The scales explored require a relativistic description, in addition to statistical tools for their analysis. In this thesis, we study the effects of adding relativistic and primordial non-Gaussianity contributions to the power spectrum. We begin by reviewing the standard cosmology, then we present the cosmological and Newtonian perturbation theory, which are necessary mathematical tools in the computation of our main results. Afterwards we present the main contributions to this thesis. First, we present solutions to the Einstein equations in the long-wavelength approximation, this allow us to obtain expressions for the relativistic density power spectrum at second and third order, these expressions also include contributions from primordial non-Gaussianity, in terms of the parameters $f_{\mathrm{NL}}$ and $g_{\mathrm{NL}}$. These results are complemented with the well known Newtonian solutions for the density contrast and are used in the computation of the total (relativistic + Newtonian) one-loop power spectrum. For completeness we also calculate the bispectrum at tree-level. We discuss the possibility of these relativistic effects being detectable with the future surveys considering different limiting values for $f_{\mathrm{NL}}$ and $g_{\mathrm{NL}}$. Subsequently, we compute the real space galaxy power spectrum, including relativistic and primordial non-Gaussianity effects. These effects come from the relativistic one-loop power spectrum terms and from factors of the non-linear bias parameter $b_{\mathrm{NL}}$. We use our modelling to assess the ability of Stage-IV surveys to constrain primordial non-Gaussianity. Finally, we show how this non-linear bias parameter can effectively renormalize diverging relativistic contributions at large scales.