[NTU-NCTS String Seminar] Entanglement between two gravitating universes

  • Event Date: 2022-11-25
  • High Energy Physics and Astrophysics
  • Speaker: Prof. Tomonori Ugajin (Kyoto University)  /  Host: Profs. Yu-tin Huang & Pei-Ming Ho (NTU)
    Place: Rm. 815, Dept. of Physics, NTU

Title: [NTU-NCTS String Seminar] Entanglement between two gravitating universes
Speaker: Prof. Tomonori Ugajin (Kyoto University)​​​​​​​
Time: Nov. 25, 2022 (Fri.) 14:00-15:00
Venue: Rm. 815, Dept. of Physics, NTU

Abstract:
We study two disjoint universes in an entangled pure state. When only one universe contains gravity, the path integral for the nth Rényi entropy includes a wormhole between the n copies of the gravitating universe, leading to a standard "island formula" for entanglement entropy consistent with unitarity of quantum information. When both universes contain gravity, gravitational corrections to this configuration lead to a violation of unitarity. However, the path integral is now dominated by a novel wormhole with 2n boundaries connecting replica copies of both universes. The analytic continuation of this contribution involves a quotient by Zn replica symmetry, giving a cylinder connecting the two universes. When entanglement is large, this configuration has an effective description as a "swap wormhole", a geometry in which the boundaries of the two universes are glued together by a "swaperator". This description allows precise computation of a generalized entropy-like formula for entanglement entropy. The quantum extremal surface computing the entropy lives on the Lorentzian continuation of the cylinder/swap wormhole, which has a connected Cauchy slice stretching between the universes -- a realization of the ER=EPR idea. The new wormhole restores unitarity of quantum information.