Modern Topics in Scalar Field Cosmology

The aim of this research is to use modern techniques in scalar eld Cosmol-ogy to produce methods of detecting gravitational waves and apply them to current gravitational waves experiments and those that will be producing results in the not too distant future. In the rst chapter we discuss dark matter and some of its candidates, specically, the axion. We then address its relationship with gravitational waves. We also discuss ination and how it can be used to detect gravitational waves. Chapter 2 concentrates on constructing a multi eld system of axions in order to increase the mass range of the ultralight axion, putting it into the observation range of pul-sar timing arrays. Chapter 3 discusses non-attractor ination which is able to enhance stochastic background gravitational waves at scales that allows them to be measured by gravitational wave experiments. Chapter 4 uses a similar method to chapter 3 and applies it to 3-point overlap functions for tensor, scalar and a combination of the two polarisations.