Holographic Space-time Models of Anti-deSitter Space-times
  We study the constraints on HST models of AdS space-time. The causal diamonds of HST along time-like geodesics of AdS space-time, fit nicely into the FRW patch of AdS space. The coordinate singularity of the FRW patch is identified with the proper time at which the Hilbert space of the causal diamond becomes infinite dimensional. For diamonds much smaller than the AdS radius, RAdS, the time dependent Hamiltonians of HST are the same as those used to describe similar diamonds in Minkowski space. In particular, they are invariant under the fuzzy analog of volume preserving diffeomorphisms of the holographic screen, which leads to fast scrambling of perturbations on the horizon of a black hole of size smaller than RAdS. We argue that, in order to take a limit of this system which converges to a CFT, one must choose Hamiltonians, in a range of proper times of order RAdS, which break this invariance, and become local in a particular choice of basis for the variables. We show that, beginning with flat, sub-RAdS, patches of dimension D, the resulting CFT, constructed from the variables of HST, is inconsistent with the entropy of large black holes, unless one has at least two compact dimensions, whose size is of order RAdS. The argument is connected to a new observation about the scrambling rate of information localized on the compact dimensions. Our construction explains why large AdS black holes do not have the fast scrambling property. Our present approach cannot deal with models where string theory is weakly coupled and RAdS is of order the string scale, because the relationship between area and entropy is non-universal in such models. On spatial length scales longer than RAdS, our mapping of HST variables into CFT shares much with the Tensor Network Renormalization Group (TNRG)[1] and is a sort of evolving error correcting code[2]. 
Tom Banks and Willy Fischler
hep-th gr-qc