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Islands and mixed states in closed universes

Fallows, Seamus; Ross, Simon F.

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Seamus Fallows
PGR Student Doctor of Philosophy


We investigate the appearance of islands when a closed universe with gravity is entangled with a non-gravitating quantum system. We use braneworlds in three-dimensional multiboundary wormhole geometries as a model to explore what happens when the non-gravitating system has several components. The braneworld can be either completely contained in the entanglement wedge of one of the non-gravitating systems or split between them. In the former case, entanglement with the other system leads to a mixed state in the closed universe, unlike in simpler setups with a single quantum system, where the closed universe was necessarily in a pure state. We show that the entropy of this mixed state is bounded by half of the coarse-grained entropy of the effective theory on the braneworld.


Fallows, S., & Ross, S. F. (2021). Islands and mixed states in closed universes. Journal of High Energy Physics, 2021(7), Article 22.

Journal Article Type Article
Acceptance Date Jun 17, 2021
Online Publication Date Jul 6, 2021
Publication Date 2021
Deposit Date Jul 9, 2021
Publicly Available Date Oct 21, 2021
Journal Journal of High Energy Physics
Print ISSN 1126-6708
Publisher Scuola Internazionale Superiore di Studi Avanzati (SISSA)
Peer Reviewed Peer Reviewed
Volume 2021
Issue 7
Article Number 22
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Copyright Statement
Open Access . This article is distributed under the terms of the Creative Commons Attribution License (CC-BY 4.0), which permits any use, distribution and reproduction in any medium, provided the original author(s) and source are credited.

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