Axions in Cosmology
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Axions in Cosmology


This thesis is based on two main projects completed during my graduate studies. The first project consists of showing that hybrid inflationary theories are still viable meaning that there is a parameter space that give us cosmological parameters in agreement with the Planck data.The second project explore the mixing between gravity wave, electromagnetic waves and axion waves in a curved space time as a way to potentially detect dark matter. We revisit two-field hybrid inflation as an effective field theory for low-scale inflation with sub- Planckian scalar field ranges. We focus on a prototype model by Stewart because it allows for a red spectral tilt, which still fits the current data. We describe the constraints on this model imposed by current CMB measurements. We then explore the stability of this model to quantum corrections. We find that for relevant, marginal, and at least a finite set of irrelevant operators, some additional mechanism is required to render the model stable to corrections from both quantum field theory and quantum gravity. We outline a possible mechanism by realizing the scalars as compact axions dual to massive 4-form field strengths, and outline how natural hybrid inflation may be supported by strong dynamics in the dual theory. We describe bosonic (scalar, electromagnetic and gravitational) wave mixing in curved space- time. Curved spacetime adds a new length scale, the Schwarzschild radius, which significantly alters the oscillation probabilities in comparison to the standard flat spacetime computations. The alterations are analogous to the Mikheyev-Smirnov-Wolfenstein (MSW) effect for neutrinos and are “frozen- in” as the outgoing gravitational and/or electromagnetic wave propagates away from a compact object. Although we consider the axion and axion-like particles, our computations iii are largely model independent and applicable for generic spin-zero dark matter. We describe the probabilities for axions and generic bosonic dark matter oscillations. We describe some of the ob- servational consequences of the mixing including the energy and polarization of the waves exiting the compact object.

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