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New directions in cosmology and astrophysics

Aug, 2020
263 pages
Supervisor:
Thesis: PhD
  • Imperial Coll., London
(2020)
  • Published: Aug, 2020
DOI:
URN/HDL:
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Abstract: (Imperial Coll., London)
To a good approximation, our Universe is flat and homogeneous, strongly suggesting a period like inflation, a rapid accelerated expansion, in the early Universe. We believe inflation also transformed quantum mechanical perturbations to classical, seeding the large-scale structure today. Overwhelming empirical evidence suggests, moreover, that these perturbations were nearly Gaussian and are well described by adiabatic initial conditions that are predicted by the simplest inflationary models. Following inflation, we find the Universe can be characterised by the LCDM model which has become the bedrock of modern cosmology, and survived many challenges from the influx of cosmological data in the past decade. In the upcoming years, however, the field of cosmology will see a wealth of new and high quality data from the current Stage-3 (and the forthcoming Stage4) surveys of the cosmic microwave background (CMB) and large-scale structure (LSS). Simultaneously, low-frequency gravitational wave background (GWB) observations with pulsar-timing arrays (PTAs) and surveys of the 21cm hydrogen-line will achieve sufficient accuracy for cosmological inference. These create unique and exciting opportunities to study the fundamental components of the Universe. These experiments will provide the strongest challenges to our modern cosmological picture yet, and have the potential of revolutionising our understanding of the most fundamental properties of our Universe. In this work I discuss various new opportunities provided by upcoming precision measurements of CMB and galaxy surveys, as well as the upcoming measurements of 21cm hydrogen brightness temperature. This thesis utilises some of these upcoming cosmological probes for the detection of physics different than what is predicted by ΛCDM with the simplest inflationary models.