Axions and the Evolution of Structure in the Universe

A cosmological scenario where axions provide the dark matter in the universe is considered. Fluctuations in the axion-field energy density produced by domain walls and strings cause the appearance of "axion clumps" of masses of order ${10}^6{M}_{\odot }$ which most likely collapse to black holes by or at the time that the universe becomes axion dominated at $T\sim 10$ eV. These objects form the building blocks for the clustering hierarchy theory of galaxy and supercluster formation on scales up to ∼ 10 Mpc and ${10}^{15}{M}_{\odot }$.