Holographic Lorentz and Carroll Frames

It has been shown that the solution space of three-dimensional gravity contains an additional free function if we relax the Bondi gauge. This additional function allows to promote the boundary metric to a Lorentz or Carroll frame, in asymptotically AdS or flat spacetimes. In this talk, we focus on the symplectic structure of this solution space, which is finite and obtained taking advantage of the built-in ambiguities. Remarkably, there is a prescription of the selected corner term that makes smooth the flat limit of the AdS symplectic structure. This prescription reveals a holographic anomaly in the boundary Lorentz symmetry, that rotates the frame, and which survives in the flat limit, thus predicting the existence of quantum anomalies in conformal Carrollian field theories.