We introduce the fuzzy dark sector (FDS) scenario as a rich, interacting system and candidate for dark matter. This serves as a natural extension of the single-component, noninteracting fuzzy dark matter (FDM) paradigm. Concretely, we consider an ultralight Abelian-Higgs model, with interacting Higgs and dark photon degrees of freedom. We find that the transfer function and hence the imprint on the cosmic microwave background and large-scale structure (LSS) are characterized by a single characteristic scale of the interacting fuzzy dark sector, allowing us to recover the LSS signature of single-field FDM, dependent on the FDS parameters. In contrast, galactic halos present a great diversity, unlike with the universality of single-field FDM, owing to the interaction between fields. This interaction introduces an instability that is not otherwise present for the case of four decoupled scalars. Finally, we comment on primordial production and portals to the Standard Model and introduce another simple realization of the fuzzy dark sector paradigm with a kinetic coupling.

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• Dark matter
• Large scale structure of the Universe
• Particle dark matter