Axions
Abstract:
Axions (and 'axion-like particles') are hypothetical particles predicted first as a solution to the charge-parity problem of QCD, and later found to emerge in more general settings involving spontaneous symmetry breaking, anomalies, and non-perturbative physics. They also emerge generically in theories with supersymmetry and extra dimensions, including string theory. I will briefly review the theory of axions before moving onto a study of their rich phenomenology, with a focus on cosmology in particular. We will cover axion dark matter, and methods to detect it, including new experimental proposals being constructed in Germany. 'Fuzzy' dark matter and its effects on the CMB and galaxy formation. Axion inflation, dark energy, and the cosmological constant problem. Searches for axions as mediators of new forces, and other laboratory effects. Axions and stellar evolution. Decays of heavy axions, and relation to collider physics. Constraints on axions from black hole physics, including gravitational waves.