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Baby Universes from Thermal Pure States in the Sachdev-Ye-Kitaev Model
Martin Sasieta1, Brian Swingle2, Alejandro Vilar López3
1University of California, Leinweber Institute for Theoretical Physics, Berkeley, California 94720, USA.
Abstract:
We construct a simple two-dimensional holographic model of a closed "baby" universe. The baby universe spacetime originates from the black hole interior in Jackiw-Teitelboim gravity. The holographic description is a low-temperature thermal pure state of two Sachdev-Ye-Kitaev (SYK) models. The construction of the state relies on the insertion of a heavy matter operator, which supports the baby universe, together with a first-order thermal phase transition between a black hole phase and an empty anti-de Sitter phase. For the transition, we employ a version of the Maldacena-Qi phase transition of two coupled SYK systems. The bulk entanglement between the anti-de Sitter region and the baby universe remains O(N) below the transition, owing to the large number of light bulk fields. This entanglement admits a definition through coarse-graining over SYK couplings.
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