Study of multiple axion cosmologies

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The study of axion-like particles provides an interesting and promising approach to understanding a range of physical phenomena in particle physics and the structure of the universe. Since the early days of QCD physics, it was found that that the action of QCD was permitted to contain a CP-violating term. Through the work of Peccei and Quinn it was postulated that breaking a newly introduced U(1) symmetry would give rise to a light spin zero particle known as the axion. It soon became apparent that theories suggested axions could have been created in abundance during the Big Bang. If axions presented certain properties, preventing other decay modes, the universe would be constructed with primordial axions. Axions could therefore plausibly provide an explanation to the observed dark matter density of the physical universe. The current view on the cosmology and astrophysics of axion-like particles provides a very important framework for areas such as inflation and the structural formation of the present-day expanding Universe. A generic prediction of various string theories is the presence of many axion like particles. In the context of string theory, axions appear to provide promising candidates for dark energy/dark matter evolution and explaining the cosmological constant via quintessence. Therefore, it is important that cosmological observations should be used in order to place constraints on the properties these fields might have. Understanding the evolution of these scalar fields in respect to higher order models, in order to reproduce the cosmological observations of the universe we observe today, will serve as a foundation to this project by investigating multiple axion cosmologies.