Femtolensing and Picolensing by Axion Miniclusters

Non-linear effects in the evolution of the axion field in the early Universe may lead to the formation of gravitationally bound clumps of axions, known as ``miniclusters.'' Minicluster masses and radii should be in the range $M_{\rm mc}\sim10^{-12} M_\odot$ and $R_{\rm mc} \sim 10^{10}$cm, and in plausible early-Universe scenarios a significant fraction of the mass density of the Universe may be in the form of axion miniclusters. If such axion miniclusters exist, they would have the physical properties required to be detected by ``femtolensing.''