| Abstract: | The dark matter landscape, ranging from fuzzy dark matter to primordial black holes, spans more than 90 orders of magnitude in mass. We will discuss how new and upcoming cosmological observables can probe models that lie on the extreme ends of this spectrum. We will first present an updated picture of the scenario of primordial black holes as dark matter. Placing an emphasis on the stellar-mass window motivated by the most recent LIGO detections, we will introduce constraints from astrophysical transients such as gravitational waves from merging black holes, fast radio bursts and more. We will then turn to the 21cm global signal at cosmic dawn, and advocate for its unique sensitivity to interactions between the dark and visible sectors. In particular, we will discuss the suggested dark matter explanation for the recently claimed detection of an anomalous 21cm absorption profile by the EDGES experiment, showing that the viable parameter space is highly fine-tuned. Finally, we will demonstrate how a robust detection of the 21cm global signal at cosmic dawn can be used to place the strongest constraints to date on models of ultra-light hidden-photon dark matter. |