Cold and fuzzy dark sector

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, non-interacting Fuzzy Dark Matter (FDM) paradigm. Concretely, we consider an ultra-light Abelian-Higgs model, with interacting Higgs and dark photon degrees of freedom. We find that the transfer function, and hence imprint on the CMB and Large-Scale Structure (LSS), is 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.