2026-09-23T18:45:42Zhttps://api.repository.cam.ac.uk/server/oai/request

oai:www.repository.cam.ac.uk:1810/3375902023-12-22T14:04:34Zcom_1810_205871com_1810_256064col_1810_206446

Reconstructing the Sky with CMB Lensing methods 10.17863/CAM.85000 Darwish, Omar Sherwin, Blake Current and future high significance CMB lensing-galaxy cross-correlations will soon precisely probe the growth of structure and provide powerful tests for parameter tensions, non-Gaussianity, neutrino mass, and modifications to Λ−CDM and gravity. However, such cross-correlations are sensitive to CMB foreground contamination, and the resulting biases represent an important challenge for cosmological analyses. In this thesis we describe new CMB lensing cross-correlation measurements and a novel multi-frequency cleaning-based technique to mitigate foreground effects in lensing maps. In particular, we present a tSZ cleaned cross-spectrum between Atacama Cosmology Telescope lensing and BOSS galaxies using a modified version of the standard quadratic estimator that retains most of the signal-to-noise. To minimize lensing foreground biases, geometry-based methods that modify the form of the standard quadratic estimator have been developed as well. We discuss how to optimally combine these with multi-frequency cleaned data to mitigate the impact of foreground contamination while maintaining maximal significance. For a Simons Observatory-like experiment, we find that for the CMB lensing auto-spectrum it is possible to reduce the foreground induced bias by a large factor, compared to the standard quadratic estimator, at a modest noise cost. We find a similar result for a cross-correlation with an LSST-like sample, with a large reduction in bias at small noise cost. Finally, we turn to the three-dimensional large scale structure of the Universe probed by galaxy surveys. We show how we can reconstruct the large-scale density field from galaxy modes using CMB lensing-inspired methods and use this reconstruction to improve constraints on local primordial non-Gaussianity. University of Cambridge 2021-11-21 Thesis Doctoral eng STFC-CDT https://www.repository.cam.ac.uk/handle/1810/337590 https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/126a310b-3955-4834-b4ae-19cf190b67b6/download bc3d5a9a74c02b89683f90940b851a96 https://www.rioxx.net/licenses/all-rights-reserved/ cosmology cmb cmb lensing large-scale structure