Flat space from the Fringes: An Introduction to Carrollian Holography

The AdS/CFT correspondence currently stands unrivalled as our most complete realisation of the holographic principle. Despite its numerous successes, the story is still far from over - intrinsic questions aside, AdS is a very special spacetime, and any holographic implications we could draw may likewise be restricted. The call for a more generic understanding of the holographic principle supplanted by observations that our universe possesses a positive cosmological constant has led to renewed efforts on holography for non-AdS spacetimes, specifically those involving its siblings: dS and Minkowski. In this talk, I will discuss aspects of boundary duals to the latter. Specifically, I will first review relevant properties of asymptotically flat spacetimes. In so doing, it will become clear that putative co-dimension one boundary duals must live atop a strange non-Lorentzian background known as a Carroll structure. With this motivation, I will formally define Carroll structures, remark on their symmetries and construct Carroll covariant theories. I will comment on their properties and tentative holographic interpretations, then conclude with an overview of current questions and future directions.