Pedersen, Christian Thomas;
(2021)
Neutrino mass and cosmology from the Lyman-alpha forest.
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
The Lyman-alpha forest (Lyaf) is a series of absorption features in the spectra of high redshift quasars, which contains valuable cosmological information on the small-scale clustering of matter at 5>z>2. This information is highly complementary to observations of the CMB in constraints on parameters that affect the relative amplitude of clustering on small and large scales, such as neutrino mass and the shape of the primordial power spectrum. A unique feature of the Lyaf is that it probes the Universe at a period that is close to Einstein-de Sitter, where the expansion and growth rate are close to independent of cosmological model. Early analysis of the Lyaf recognised this implied that the cosmological information in the Lyaf was contained in the linear matter power spectrum. In this thesis, we revisit this idea at the level required by current and upcoming datasets, with an emphasis on observations of the upcoming Dark Energy Spectroscopic Instrument (DESI). First we present a set of simulations studying a degeneracy in the 1D and 3D Lyaf flux power spectra between neutrino mass and the amplitude of the primordial power spectrum, A_s. We find that the degeneracy persists to percent level differences in both the 1D and 3D flux power spectra. Second, we present a Gaussian process emulator to predict the Lyaf flux power spectrum as a function of the linear power spectrum and the state of the IGM at the epoch of interest. We show that the emulator is able to model the 1D flux power spectrum of the Lyaf to sub-percent accuracy in cosmologies outside of the training set, which we demonstrate in the case of massive neutrinos. Finally, we investigate the possibility of compressing the cosmological information in the 1D flux power spectrum into marginalised constraints on the amplitude and slope z=3 linear theory power spectrum, streamlining access to this information without the need for cosmologists to perform their own marginalisation over astrophysical and instrumental contaminants. This was last done with SDSS-I analysis in 2005, and we test this compression at the level of the upcoming DESI dataset. Preliminary results indicate that the two-parameter compression loses information in the case of massive neutrino cosmologies, but adding a third shape parameter to the description of the linear power spectrum could capture this missing information.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | Neutrino mass and cosmology from the Lyman-alpha forest |
| Event: | UCL |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Copyright © The Author 2021. 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 Physics and Astronomy |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10138787 |
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