Cosmology from the bispectrum

Abstract

With a suite of current and up-coming experiments set to provide us the with exquisite

measurements of the sky in a wide range of frequencies, we are posed with the problem of

how to maximally utilize these data sets. Historically two-point function measurements have

been the tool of choice, and they have been highly effective. However, two-point functions

are unable to extract all the available information, particularly on the small, non-linear

scales. With the goal of providing complimentary measurements to the power spectrum, we

use the bispectrum to explore a range of physical processes.

In the first half of this thesis, we discuss two applications of the bispectrum to probe large

scale structure. Firstly, we measure the bispectrum from secondary anisotropies of the

cosmic microwave background using data from the Atacama Cosmology telescope and the

Planck Satellite. Secondly, we use a suite of simulations to explore the bispectrum of weak

lensing shear maps. Using these simulations, we explore how bispectrum measurements

can be used to enhance our ability to measure cosmological parameters, including the sum

of the masses of the neutrinos. We find that, for an experiment like the Large Synoptic Sky

Survey, including information from the bispectrum will enhance parameter constraints by

30%.

In the second half of this thesis, we discuss two aspects regarding primordial gravitational

waves. First, we discuss how measurements of the bispectrum can be used to probe

primordial non-Gaussianity between tensor and scalar fields and present our preliminary

constraints on interactions between these fields. Secondly, we discuss how bispectrum

measurements of galactic foregrounds, including polarised dust and synchrotron emission,

have the potential to help discriminate between the desired signal from primordial gravity

waves and galactic contaminants.