Primordial Spectral Distortions Originating from Cosmological Perturbations

Abstract

The anisotropies in the light arriving from the Cosmic Microwave Background (CMB) have provided cosmologists with a wealth of information over the previous two decades. Arguably this dataset has allowed cosmology to evolve into the role of precision science that it occupies today. This is due to the theoretical, mathematical and computational tools that link these anisotropies to the primordial perturbations that seeded structure in our Universe. Spectral distortions of the CMB present a separate and complementary source of information from the night sky. Consisting of small deviations from the otherwise blackbody shape of the CMB spectrum, these signals probe the thermal history of the Universe at earlier times than recombination, offering a insight into the physics of the primordial plasma. This thesis will explore connections between primordial perturbations and spectral distortions from two main viewpoints: Firstly the sourcing of average distortions from the dissipation of energy arising from these perturbations, with a particular focus on tensorial perturbations (papers 1-2, chapters 4-5). Secondly the prospect of studying a spatially varying distortion signal across the CMB, analogously to the usual CMB anisotropies (papers 3-5, chapters 6-8). In the aim of completeness chapter 1 will review the introductory cosmology necessary to interpret the other chapters. Chapter 2 will introduce the photon spectrum in detail, covering both temperature shifts and distortions to the blackbody spectrum irreconcilable with changes of temperature. Chapter 3 will introduce cosmological perturbation theory, the framework which explains how small perturbations evolve in the otherwise homogeneous expanding Universe.

Date of Award	29 Mar 2023
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Jens Chluba (Main Supervisor) & Richard Battye (Co Supervisor)