TY  - JOUR
PB  - SciPost Foundation
DO  - 10.21468/SciPostPhys.19.6.143
TI  - Entangled universes
PY  - 2025/12/01
UR  - https://www.scipost.org/SciPostPhys.19.6.143
JF  - SciPost Physics
JA  - SciPost Phys.
VL  - 19
IS  - 6
SP  - 143
A1  - Gupta, Divij
AU  - Headrick, Matthew
AU  - Sasieta, Martin
AB  - We propose a generalization of the RT and HRT holographic entanglement entropy formulas to spacetimes with asymptotically Minkowski as well as asymptotically AdS regions. We postulate that such spacetimes represent entangled states in a tensor product of Hilbert spaces, each corresponding to one asymptotic region. We show that our conjectured formula has the same general properties and passes the same general tests as the standard HRT formula. We provide further evidence for it by showing that in many cases the Minkowski asymptotic regions can be replaced by AdS ones using a domain wall. We illustrate the use of our formula by calculating entanglement entropies between asymptotic regions in Brill-Lindquist spacetimes, finding phase transitions similar to those known to occur in AdS. We construct networks of universes by gluing together Brill-Lindquist spaces along minimal surfaces. Finally, we discuss a variety of possible extensions and generalizations, including to universes with asymptotically de Sitter regions; in the latter case, we identify an ambiguity in the homology condition, leading to two different versions of the HRT formula which we call "orthodox" and "heterodox", with different physical interpretations.
ER  -

@Article{10.21468/SciPostPhys.19.6.143,
	title={{Entangled universes}},
	author={Divij Gupta and Matthew Headrick and Martin Sasieta},
	journal={SciPost Phys.},
	volume={19},
	pages={143},
	year={2025},
	publisher={SciPost},
	doi={10.21468/SciPostPhys.19.6.143},
	url={https://scipost.org/10.21468/SciPostPhys.19.6.143},
}