2020/08/31 by Vijay Balasubramanian, Arjun Kar, Tomonori Ugajin · 1 citation
Physics and Astronomy · #hep-th
paper · pdf · doi:10.1007/jhep02(2021)136
30 pages, 7 figures, references added, improved discussion
arxiv created 2020/12/24 · arxiv updated 2021/03/17
We use the replica method to compute the entanglement entropy of a universe without gravity entangled in a thermofield-double-like state with a disjoint gravitating universe. Including wormholes between replicas of the latter gives an entropy functional which includes an "island" on the gravitating universe. We solve the back-reaction equations when the cosmological constant is negative to show that this island coincides with a causal shadow region that is created by the entanglement in the gravitating geometry. At high entanglement temperatures, the island contribution to the entropy functional leads to a bound on entanglement entropy, analogous to the Page behavior of evaporating black holes. We demonstrate that the entanglement wedge of the non-gravitating universe grows with the entanglement temperature until, eventually, the gravitating universe can be entirely reconstructed from the non-gravitating one.