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Testing extensions to the standard model of cosmology with the growth of structure

Stafford, S (2022) Testing extensions to the standard model of cosmology with the growth of structure. Doctoral thesis, Liverpool John Moores University.

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Abstract

The past century has seen cosmologists piece together a working theory for the origin and evolution of structure in the Universe which has been hugely successful at describing a wide range of observations. This theoretical paradigm is called the LCDM model, which describes the two main constituents of our Universe: L, representing dark energy which drives the late-time accelerated expansion of space and CDM, representing cold dark matter, the main matter constituent of our Universe. Despite this, this thesis lays out some of the current tensions which have arisen with the current concordance model of cosmology and uses these to motivate exploring extensions to LCDM. The thesis is comprised of three main parts; in the first part I explore one of the predictions of inflation, which is a non-zero running of the scalar spectral index -- usually set to be zero in the LCDM model -- and its effects on the formation and evolution of large-scale structure. In particular I examine its effects on the abundance (through the halo mass function), distribution (through the two point auto-correlation function) and internal properties (through total matter density profiles) of dark matter haloes, finding effects of the order 10% in all of these quantities when comparing to a LCDM simulation. I also show that these effects due to cosmology are separable from the effects present due to galaxy formation physics to typically better than 1% accuracy. In the second part of this thesis, I focus on the effects warm dark matter, self-interacting dark matter and a running scalar spectral index have on galaxy scales, with particular focus on Milky Way mass haloes. In this part of the thesis I explore the degeneracies present between the effects of these different cosmological models on the abundance and distribution of substructure, as well as the distribution of matter inside host haloes in dark matter-only simulation. In general these models all show strong degeneracies in their effects, but in detail differences can be discerned. This part of the thesis also illustrates the degeneracy between the effects from baryons and galaxy formation physics and cosmological effects. In the third and final part of this thesis I explore whether future stage-IV weak lensing surveys will be able to place independent and competitive constraints on the parameters associated with the aforementioned extensions M_WDM, σ/m, α_s). This is done using the non-linear matter power spectrum extracted from dark matter-only simulations to compute the cosmic shear power spectrum. I then compute a realistic set of error bars associated with the cosmic shear power spectrum which are representative of future upcoming surveys, taking into account the expected sky coverage, number density of source galaxies, and associated shape noise. I find that weak lensing should be able to place useful, independent, constraints on each of these cosmological parameters, supporting current observational efforts in doing so.

Item Type: Thesis (Doctoral)
Uncontrolled Keywords: cosmology
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Divisions: Astrophysics Research Institute
Date Deposited: 10 Jan 2022 09:05
Last Modified: 10 Jan 2022 09:05
DOI or Identification number: 10.24377/LJMU.t.00015991
Supervisors: McCarthy, I, Font, A and Crain, R
URI: https://researchonline.ljmu.ac.uk/id/eprint/15991

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