DeSitter entropy, quantum entanglement and AdS/CFT

A de Sitter brane-world bounding regions of anti-de Sitter space has a macroscopic entropy given by one-quarter the area of the observer horizon. A proposed variant of the AdS/CFT correspondence gives a dual description of this cosmology as conformal field theory coupled to gravity in de Sitter space. In the case of two-dimensional de Sitter space this provides a microscopic derivation of the entropy, including the one-quarter, as quantum entanglement of the conformal field theory across the horizon.