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  • Open Access

Entanglement Entropy as a Probe beyond the Horizon

Konstantinos Boutivas*, Dimitrios Katsinis†, Georgios Pastras‡,∥, and Nikolaos Tetradis§

  • *Contact author: kboutivas@phys.uoa.gr
  • †Contact author: dkatsinis@phys.uoa.gr
  • ‡Also at Laboratory for Manufacturing Systems and Automation, Department of Mechanical Engineering and Aeronautics, University of Patras, 26110 Patra, Greece.
  • §Contact author: ntetrad@phys.uoa.gr
  • ∥Contact author: pastras@lms.mech.upatras.gr
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Phys. Rev. Lett. 135, 061602 – Published 4 August, 2025

DOI: https://doi.org/10.1103/mmd6-7zzl

Abstract

The entanglement entropy of a free field in de Sitter space is enhanced by the squeezing of its modes. We show analytically that the expansion induces a term in the entanglement entropy that depends logarithmically on the size of the overall system, which may extend beyond the horizon. In cosmology the size of the system can be identified with the size of a spatially finite universe or with the wavelength of the first mode that exited the horizon in the beginning of inflation.

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Numerical calculation of entanglement entropy in de Sitter space

Konstantinos Boutivas, Dimitrios Katsinis, Georgios Pastras, and Nikolaos Tetradis
Phys. Rev. D 111, 065010 (2025)

Article Text

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Outline

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Phys. Rev. Lett. 135, 061602– Published 4 August, 2025
  • Received 28 July 2024
  • Revised 14 February 2025
  • Accepted 18 June 2025
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.

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