Date and time: November 12th at 10:30 AM CET

Speaker: Julia Stadler

Abstract: Axions can be produced in the early universe at very low momenta by the misalignment mechanism and provide an excellent candidate for dark matter. However, the resulting axion population is expected to exhibit large inhomogeneities, if the Peccei Quinn symmetry is restored after inflation. Such fluctuation of $\mathcal(O)(1)$ collapse very early, around matter radiation equality, and form dense lumps of dark matter called axion miniclusters. The relevant mass scale for axion miniclusters is about $10^{-12} M_\astrosun$. Not only could the miniclusters dramatically modify direct detection constraints but also would they offer a new way of testing axion dark matter -- via their gravitational lensing signal. Cosmological defects, inevitablely present in cosmological scenarios which lead to minicluster formation, and a large separation of scales make the prediction of the density contrast challenging. The density contrast, however, determines the mass spectrum and fraction of dark matter defined in miniclusters.



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