| Abstract: The last few decades have witnessed the birth and rapid progress of high-precision cosmology, thanks, especially, to high-resolution, high-sensitivity cosmic microwave background (CMB) measurements. In particular, we have now quantified to sub-percent precision the abundance of dark matter, an unknown substance which makes up most of the mass of galaxies, yet is seemingly invisible. Dark matter’s nature remains one of the most salient questions in modern physics and astronomy, and many candidates — ranging from new elementary particles to primordial black holes — remain viable. In this talk, I will first review the basics physics underlying the CMB and highlight some recent advances in our theoretical understanding. Second, I will discuss novel ways to test possible interactions of particle-dark matter with visible matter, relying on seldom-used properties of CMB measurements. Third, I will talk about observational tests of primordial black holes, both with the CMB, and with gravitational waves, which have recently opened up a new window into the Universe. In closing, I will discuss recent forays into the field of low-frequency gravitational-wave measurements by pulsar timing arrays, which could be the Next Big Thing in astrophysics and cosmology. |