Probes of cosmic inflation: from the CMB to quantum analogues
type: CreativeWork
description: This thesis presents the development of data analysis and numerical simulation methods to probe the physics of inflation, a brief period of exponential expansion thought to have occurred a fraction of a second after the Big Bang. Although inflation provides the initial conditions for standard cosmological evolution and the seeds for structure formation, its underlying mechanism remains poorly understood. This motivates the search for inflationary signatures in the temperature and polarization anisotropies of the cosmic microwave background (CMB). The first part of the thesis focuses on parity-odd B-mode polarization patterns, which are a distinctive imprint of primordial gravitational waves (PGW) on large scales. The Simons Observatory (SO), a new ground-based CMB experiment, is targeting these B-modes with unprecedented sensitivity. Realizing the full potential of this high-precision instrument requires mitigating polarized Galactic foregrounds and secondary B-modes induced by weak gravitational lensing. In Chapter 2, we implement an analysis pipeline relying on multi-frequency observations and a lensing B-mode template to extract the primordial signal with optimal precision. Validated on SO-like simulations, this method removes 65% of the lensing B-modes, yields unbiased estimates of the PGW amplitude (parametrized by the tensor-to-scalar ratio r), and reduces statistical errors by 27–37%. In Chapter 3, we combine data from the Atacama Cosmology Telescope (ACT), the unWISE galaxy catalog, and Planck to reconstruct the actual CMB lensing field. Our combined tracer is 55–85% correlated with the true lensing convergence and the resulting B-mode template achieves a delensing efficiency of 47%, the highest demonstrated on real observations to date. The preliminary correlation of this template with early SO polarization maps at 93 and 145 GHz leads to the first positive detection (at 3.5σ and 4.9σ, respectively) of lensing B-modes with SO. Beyond its five-year nominal m…
abstract: This thesis presents the development of data analysis and numerical simulation methods to probe the physics of inflation, a brief period of exponential expansion thought to have occurred a fraction of a second after the Big Bang. Although inflation provides the initial conditions for standard cosmological evolution and the seeds for structure formation, its underlying mechanism remains poorly understood. This motivates the search for inflationary signatures in the temperature and polarization anisotropies of the cosmic microwave background (CMB). The first part of the thesis focuses on parity-odd B-mode polarization patterns, which are a distinctive imprint of primordial gravitational waves (PGW) on large scales. The Simons Observatory (SO), a new ground-based CMB experiment, is targeting these B-modes with unprecedented sensitivity. Realizing the full potential of this high-precision instrument requires mitigating polarized Galactic foregrounds and secondary B-modes induced by weak gravitational lensing. In Chapter 2, we implement an analysis pipeline relying on multi-frequency observations and a lensing B-mode template to extract the primordial signal with optimal precision. Validated on SO-like simulations, this method removes 65% of the lensing B-modes, yields unbiased estimates of the PGW amplitude (parametrized by the tensor-to-scalar ratio r), and reduces statistical errors by 27–37%. In Chapter 3, we combine data from the Atacama Cosmology Telescope (ACT), the unWISE galaxy catalog, and Planck to reconstruct the actual CMB lensing field. Our combined tracer is 55–85% correlated with the true lensing convergence and the resulting B-mode template achieves a delensing efficiency of 47%, the highest demonstrated on real observations to date. The preliminary correlation of this template with early SO polarization maps at 93 and 145 GHz leads to the first positive detection (at 3.5σ and 4.9σ, respectively) of lensing B-modes with SO. Beyond its five-year nominal m…
author: Hertig, Emilie Marie
language: eng
keywords: Cosmology, Inflation, Primordial Gravitational Waves, Cosmic Microwave Background, Quantum Field Theory, False Vacuum Decay
license: https://www.repository.cam.ac.uk/bitstreams/2e278e1e-41c9-4fd8-860f-5c5f428bc1bd/download
license: http://purl.org/NET/rdflicense/allrightsreserved
date published: 2025-08-27
date modified: 2026-07-22T22:24:28Z
provider: Cambridge University
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: University of Cambridge

PropertyValue
property ID: DOI
value: 10.17863/CAM.124203