A Fuzzy Axiverse from String Theory

Abstract: In this talk, I showcase models for fuzzy axion dark matter within the framework of type IIB string theory, focusing on axions originating from the Ramond-Ramond four-form in compactifications on Calabi-Yau orientifold hypersurfaces. These models are amenable to cosmological tests if a substantial relic abundance of fuzzy dark matter is produced. I present a topologically exhaustive ensemble of more than 350{,}000 Calabi-Yau compactifications with up to seven axions together with a systematic analysis of the misalignment production of fuzzy dark matter. The resulting dark matter composition is generally a mixture of fuzzy axions and heavier axions, including the QCD axion. Dark photons frequently emerge due to the orientifold projection. I will also comment on applications of optimisation strategies based on automatic differentiation for exploring the string axiverse. This talk is partially based on arXiv:2412.12012.