Edge modes as dynamical frames: charges from post-selection in generally covariant theories

Understand

We develop a framework based on the covariant phase space formalism that identifies gravitational edge modes as dynamical reference frames.

• They enable the identification of the associated spacetime region and the imposition of boundary conditions in a gauge-invariant manner.
• While recent proposals considered the finite region in isolation and sought the maximal symmetry algebra compatible with that perspective, we regard it as a subregion embedded in a global spacetime and study the symmetries consistent with such an embedding.
• This clarifies that the frame, although appearing as "new" for the subregion, is built out of the field content of the complement.