Properties of causal holographic information

In the context of the AdS/CFT correspondence, there are two natural bulk surfaces associated to a subregion of the CFT: the minimal area surface and the "causal information surface" [1]. While the area of the minimal area surface appears to compute the entanglement entropy of the subregion, it is not yet clear what CFT quantity the causal information surface computes. We investigate the properties of causal holographic information, focusing in particular on the universal coefficient of the logarithmically divergent term. We find that this coefficient contains a novel conformal invariant that cannot be written as an integral of local quantities. By considering higher curvature corrections in the bulk, we identify the coefficient of the a and c central charges in 4 dimensions. Finally, we speculate about which CFT quantity could correspond to causal holographic information.