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Ensuring Accurate Cosmology from the Era of High-precision Cosmic Shear Surveys

Deshpande, Anurag Chandrahas; (2023) Ensuring Accurate Cosmology from the Era of High-precision Cosmic Shear Surveys. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

Two of the fundamental components of the Universe are still poorly understood: dark energy and dark matter. Collectively, these constitute around 95% of the Universe according to our current best measurements. This stresses the need to accurately model them. A particularly powerful probe of these quantities is the effect of weak gravitational lensing. This is the distortion of images of distant galaxies due to the gravitational effects of the large-scale structure of the Universe. Upcoming weak lensing surveys, known as Stage IV experiments, are poised for more than an order-of-magnitude improvement in cosmological parameter constraining ability. Accordingly, it is paramount that the accuracy of our theoretical models keeps in step. In this thesis, I examine four previously neglected systematic effects, and report on their importance for upcoming experiments, particularly focusing on the most imminent of the Stage IV surveys, the Euclid}space telescope. I also discuss a potential mitigation strategy for them. Within this work, I first examine the impact of the reduced shear approximation and magnification bias. Specifically, I evaluate the biases in cosmological inference from neglecting these effects. For these terms, assuming a w0waCDM cosmology, I find significant biases in Ωm, σ8, ns, ΩDE, w0, and wa. I then describe how these two corrections depend on another common approximation; the Limber approximation. I find that the Limber approximation can be safely used when evaluating the reduced shear and magnification bias corrections for Stage IV. Another neglected effect I study is the Doppler-shift of galaxies towards their local over-density. I again find this effect is not significant for a Euclid-like experiment. Finally, I report on how a scale-cutting technique, k-cut cosmic shear, can be used to bypass the need for these corrections, without significantly weakening cosmological constraints.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Ensuring Accurate Cosmology from the Era of High-precision Cosmic Shear Surveys
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Copyright © The Author 2023. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request.
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Space and Climate Physics
URI: https://discovery.ucl.ac.uk/id/eprint/10166306
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