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Information Transfer with a Gravitating Bath

by Hao Geng, Andreas Karch, Carlos Perez-Pardavila, Suvrat Raju, Lisa Randall, Marcos Riojas, Sanjit Shashi

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Submission summary

Authors (as registered SciPost users): Hao Geng · Andreas Karch · Suvrat Raju · Sanjit Shashi
Submission information
Preprint Link: scipost_202102_00009v1  (pdf)
Date submitted: Feb. 5, 2021, 12:06 p.m.
Submitted by: Suvrat Raju
Submitted to: SciPost Physics
Ontological classification
Academic field: Physics
Specialties:
  • High-Energy Physics - Theory
Approach: Theoretical

Abstract

Late-time dominance of entanglement islands plays a critical role in addressing the information paradox for black holes in AdS coupled to an asymptotic non-gravitational bath. A natural question is how this observation can be extended to gravitational systems. To gain insight into this question, we explore how this story is modified within the context of Karch-Randall braneworlds when we allow the asymptotic bath to couple to dynamical gravity. We find that because of the inability to separate degrees of freedom by spatial location when defining the radiation region, the entanglement entropy of radiation emitted into the bath is a time-independent constant, consistent with recent work on black hole information in asymptotically flat space. If we instead consider an entanglement entropy between two sectors of a specific division of the Hilbert space, we then find non-trivial time-dependence, with the Page time a monotonically decreasing function of the brane angle---provided both branes are below a particular angle. However, the properties of the entropy depend discontinuously on this angle, which is the first example of such discontinuous behavior for an AdS brane in AdS space.

Current status:
Has been resubmitted

Reports on this Submission

Report #2 by Anonymous (Referee 2) on 2021-4-2 (Invited Report)

  • Cite as: Anonymous, Report on arXiv:scipost_202102_00009v1, delivered 2021-04-02, doi: 10.21468/SciPost.Report.2752

Strengths

  1. The paper is discussing an issue that is very topical, namely to what extend the island formula can be applied to a situation where the bath region that collects the Hawking radiation has dynamical gravity. The paper is therefore a very useful addition to the discussion.
  2. The paper describes concrete and novel set ups and comes with a very thorough analysis.

Weaknesses

I have not identified any specific weaknesses of the paper.

Report

The paper is discussing the really interesting question as to whether all the progress made on understanding and solving the information loss paradox using replica wormholes leading to the island formula for the entropy of the radiation can be applied to realistic black holes where the bath region far from black hole still has dynamical gravity. This gets to the heart of some of the deepest questions of quantum gravity: to what extent one can define local quantities like the entropy of a subregion in a QFT in a situation where gravity is dynamical. The paper is adding something useful to the on-going debate, is well written and I cannot see any obvious errors. The conclusion of the paper seems to back up the point of view that there is an essential difference between the cases having no gravity in the bath and cases with dynamical gravity. I can recommend its publication.
  • validity: high
  • significance: high
  • originality: good
  • clarity: high
  • formatting: excellent
  • grammar: perfect

Report #1 by Edgar Shaghoulian (Referee 1) on 2021-3-15 (Invited Report)

  • Cite as: Edgar Shaghoulian, Report on arXiv:scipost_202102_00009v1, delivered 2021-03-15, doi: 10.21468/SciPost.Report.2703

Strengths

The paper's primary strength is a concrete brane model where the radiation bath and the gravitational region are both gravitating, within which computations can still be performed. This model in particular has a surface (the interface between the two regions) that is non-gravitating and that allows nontrivial entanglement entropies to be defined and computed.

Weaknesses

The primary weakness is a philosophical one: the theme of the paper is that one is not allowed to shut off gravity in realistic scenarios like our universe where there is gravity everywhere, so they would like to consider that case. However, the nontrivial results of their paper are precisely in a situation where gravity is shut off on the interface between their two gravitating regions.

Report

This is a nice paper with novel calculations which merits publication in SciPost Physics. I would again like to highlight for the reader the non-gravitating interface on which entanglement entropy computations are performed as an interesting new feature.

Requested changes

I would suggest the authors cite Penington's 1905.08255 when introducing the "island formula" in equation (2.1).

  • validity: top
  • significance: high
  • originality: high
  • clarity: good
  • formatting: perfect
  • grammar: perfect

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