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Tunnelling to Holographic Traversable Wormholes
by Suzanne Bintanja, Ben Freivogel, Andrew Rolph
Submission summary
Authors (as registered SciPost users):  Suzanne Bintanja · Andrew Rolph 
Submission information  

Preprint Link:  scipost_202308_00046v1 (pdf) 
Date submitted:  20230830 12:12 
Submitted by:  Bintanja, Suzanne 
Submitted to:  SciPost Physics 
Ontological classification  

Academic field:  Physics 
Specialties: 

Approach:  Theoretical 
Abstract
We study nonperturbative effects of quantum gravity in a system consisting of a coupled pair of holographic CFTs. The AdS4/CFT3 system has three possible ground states: two copies of empty AdS, a pair of extremal AdS black holes, and an eternal AdS traversable wormhole. We give a recipe for calculating transition rates via gravitational instantons and test it by calculating the emission rate of radiation shells from a black hole. We calculate the nucleation rate of a traversable wormhole between a pair of AdSRN black holes in the canonical and microcanonical ensembles. Our results give predictions of nonpertubative quantum gravity that can be tested in a holographic simulation.
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Reports on this Submission
Strengths
1. This paper computes an interesting nonperturbative effect describing tunneling between three different solutions in AdS.
2. The computations are explained well with an indepth discussion of the different ensembles/boundary conditions.
3. Where relevant this work compares and contrasts with other results.
Weaknesses
1. I am somewhat skeptical that these results are relevant for the motivation mentioned in the introduction, i.e. testing gravity using holographic simulations (see the report).
2. Some effects that might be relevant (e.g. Schwinger pair production) are not discussed.
Report
This paper studies the tunneling rate between three different solutions in AdS$_4$ when coupling the two boundary CFTs: empty AdS, two (near)extremal magnetic black holes and a traversable wormhole. This is an interesting computation that is relevant to understand nonperturbative (quantum) gravity effects in holography. The results are presented clearly and as far as I can tell and have checked the computations are correct. I see a two aspects that can be improved.
First, I think the results are of interest on its own, but the authors mention in the introduction that they might be relevant for "testing gravity predictions" by simulating holographic CFTs on a quantum computer. To see these (exponentially) suppressed effects we have to work in a regime where there is no semiclassical bulk dual. Can we even sharply distinguish between the different bulk solutions in this case?
Second, the authors study an extremal magnetic black hole solution with massless charged Dirac fermions. They view these solutions as ground states, but I expect these solutions to be unstable under Schwinger pair production. A discussion how this influences their results (or why it does not) would be useful.
Requested changes
1. Clarify precisely what the authors have in mind when they mention they want to test gravity outside of the semiclassical regime using holographic simulations. Is there a sharp prediction they want to test? Can we even define these different (semi)classical solutions?
2. Explain why the extremal black holes can be viewed as ground states. If not, why is Schwinger pair production not a relevant decay channel.
3. Add a reference to https://arxiv.org/abs/2004.06084. This paper showed that nearextremal magnetic black holes are highly unstable. This seems relevant for the results of this paper for nearextremal black holes such as in Sec. 5.1.