Cite as: doi:10.26081/K6V913

**
I will discuss how central extensions of charge algebras in
gravitational theories with null boundaries arise from anomalous
transformations of the boundary term in the gravitational action. This
parallels the way in which the holographic Weyl anomaly appears in
AdS/CFT, with the ambiguity in the normalization of the null generator
acting analogously to the choice of Weyl frame. This entails
understanding the covariant phase space of gravitational subregions
which are open Hamiltonian systems. I will describe how to obtain
unambiguous expressions for gravitational charges within this formalism,
motivated both by AdS/CFT and by the variational principle for
gravitational subregions. As an application, I will analyze the
near-horizon Virasoro symmetries of black holes and give a systematic
derivation of the central charges. I will show that the central
extension computed by the charge algebra is directly related to the
Bekenstein-Hawking entropy via the Cardy formula.
**

**
**

To download: Right-click and choose "Save Link As..."