Gravitational $SL(2,\mathbb{R})$ Algebra on the Light Cone

Understand

In a region with a boundary, the gravitational phase space consists of radiative modes in the interior and edge modes at the boundary.

• Such edge modes are necessary to explain how the region couples to its environment.
• In this paper, we characterise the edge modes and radiative modes on a null surface for the tetradic Palatini--Holst action.
• Our starting point is the definition of the action and its boundary terms.