Dark Energy and the Symbiosis Between Micro-physics and Cosmology (Naturally)

These lectures aim to highlight the remarkable symbiosis that currently exists between the physics of the very small and the physics of the very large, using the unsolved puzzle of the nature of Dark Energy as a vehicle for so doing. The lectures first summarize what we know observationally about the properties of Dark Energy (and the Dark sector more broadly) and then discuss several approaches to explain them. Along the way this involves determining the types of interactions that would on general grounds be expected to be present in the low-energy limit of fundamental theories involving the many hierarchy of scales we see around us. This includes (but is not limited to) a discussion of technical naturalness (and `t Hooft naturalness) as well as the arguments for their use as a criterion for distinguishing amongst candidate theories. Some recent approaches I find promising are briefly summarized at the end.