Probing fundamental physics with multi-wavelength cosmology

Lead Research Organisation: University of Manchester
Department Name: Physics and Astronomy

Abstract

What happened at the beginning of our Universe? Where did all the structure (e.g. stars, galaxies, the earth, etc.) come from? What is the nature of dark matter? Or the 'dark energy' responsible for accelerating the expansion of the Universe? My proposal is focused on shedding light on these profound mysteries. First, by making precise observations of the microwave emission across the sky, I will probe earlier into the Universe's history than we have ever reached before. These microwaves, emitted about 13 billion years ago by the nascent Universe, may contain very weak patterns called 'B-modes'. If detected, these B-modes would be compelling evidence that the Universe underwent a period of rapid expansion, known as 'inflation', very early on. Inflation would provide a natural explanation for structure in the Universe: quantum fluctuations in the fabric of space-time would have been stretched and amplified during the expansion, producing the initial seeds of structure from which all others have grown. A precise measurement of B-modes could also tell us about fundamental physics. If inflation did happen, then it happened at very early times when the Universe was extremely hot and dense. Under these conditions, do our laws of physics still work? A detection of B-modes would be the first step on the road to using the early Universe as a 'natural laboratory' to investigate this question. Over the next 5 years, I will analyse the data from telescopes searching for the smoking gun B-mode signature. Teasing out the tiny signal from the observations will be a huge challenge because it is expected to be much weaker than other effects in the data. For example, our own Galaxy emits microwaves which are much stronger than the B-mode signal. Equally important, imperfections in the design of the telescopes can mimic a real signal. I therefore plan to develop new techniques capable of distinguishing between the true signal and these contaminating effects. Turning to the dark energy, one of the best ways to probe this unknown is by measuring how structures have grown over the Universe's history. Because it's a repulsive force, dark energy counteracts gravity and therefore suppresses the growth of structures. A powerful way to measure this structure is the technique of gravitational lensing. As light from a distant galaxy passes by a clump of matter, it is slightly deflected (or 'lensed') by the matter's gravitational field. This effect results in slight distortions in the observed shapes of distant galaxies which one can use to infer the dark matter structure. During my fellowship, I will perform this analysis on new sky surveys in order to learn about the dark matter and dark energy. In particular I will develop and apply a new and innovative technique to measure gravitational lensing in the radio band which I have recently proposed. Using this technique, I can be sure that the distortions in the shapes of distant galaxies are really due to the lensing effect rather than being intrinsic to the galaxies themselves. Both microwave B-modes and gravitational lensing are young and extremely exciting fields of study. They are exciting because of their unique potential to probe unknown physics. The physics of the early Universe and the nature of dark energy are consistently rated, by both STFC's own advisory panels, and by international bodies, as the two most important questions facing cosmology today. The research described in this proposal will play an important role in tackling these two frontiers of scientific knowledge.

Publications

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Battye R. A. (2012) BINGO: a single dish approach to 21cm intensity mapping in arXiv e-prints

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Bonaldi A (2016) SKA weak lensing- II. Simulated performance and survey design considerations in Monthly Notices of the Royal Astronomical Society

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Bonaldi A. (2014) Foreground removal requirements for measuring large-scale CMB B modes in light of BICEP2 in Monthly Notices of the Royal Astronomical Society

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Brown M. (2015) Weak gravitational lensing with the Square Kilometre Array in Advancing Astrophysics with the Square Kilometre Array (AASKA14)

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Brown Michael L (2012) Prospects for weak lensing studies with new radio telescopes in arXiv e-prints

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Demetroullas C (2015) Cross-correlation cosmic shear with the SDSS and VLA FIRST surveys in Monthly Notices of the Royal Astronomical Society