Axions and the Lightest DM Candidate
David Marsh (Universität Göttingen)

Axions are a hypothetical class of particle which may constitute all, or a part of, the dark matter in the Universe. Due to their unique symmetry properties, they are the lightest viable dark matter candidate, with the mass possibly being as low as 1e-22 eV. I will discuss how this lower limit is derived from observations of the cosmic microwave background anisotropies, and the abundance of galaxies at high redshift, and the observed spin distribution of supermassive black holes. At the lower mass limit, axions manifest novel wavelike behaviour in the inner regions of galaxies that can be used to search for evidence of them in stellar motions. Direct detection of such ultralight axions is extremely challenging, and I will discuss some ideas.