Reconstructing the Sky with CMB Lensing methods

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.

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2021

Author dc:creator

• Darwish, Omar

Advisor dc:contributor.advisor

• Sherwin, Blake

• cosmology
• cmb
• cmb lensing
• large-scale structure

Licence

• https://www.rioxx.net/licenses/all-rights-reserved/

Language dc:language

eng

DOI dc:identifier.doi

https://doi.org/10.17863/CAM.85000

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/337590