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

Preprint Link:  scipost_202308_00046v2 (pdf) 
Date accepted:  20240221 
Date submitted:  20240205 11:22 
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.
Author comments upon resubmission
We thank the referee for their insightful questions and comments. Below we address each of the comments in turn.
 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?
Let us first clarify what we mean by semiclassical. The solutions, like the traversable wormhole, are welldefined semiclassical solutions (in the sense of being solutions to Einstein’s equations using ⟨Tμν ⟩). What is outside of the semiclassical regime is the instanton tunnelling rate, in the sense that it is nonperturbative in GN ℏ, and that rate is the prediction that we would in principle want to test. For fixed temperature, the canonical ensemble, the rate is given by (1.4), while for fixed energy, the microcanonical ensemble, it is given by (1.3). Within our regime of validity, these tunnelling rates are small, exponentially suppressed, but nonzero.
We have added a sentence towards the end of the third paragraph of the introduction for clarification.
 Explain why the extremal black holes can be viewed as ground states. If not, why is Schwinger pair production not a relevant decay channel.
The semiclassical solution which is a pair of extremal black holes is not the true ground state outside of the bottom right of the region of parameter space shown in our Fig 1. We explicitly compare the energies of the different solutions in Sec 3 and find the regions of parameter space where either the traversable wormhole or empty AdS solutions have lower energy. It is true that AdSRN black holes can develop instabilities as they approach extremality, zero temperature, as investigated for example in [1–7]. We are investigating another kind of instability; in our paper, we are calculating the fixedenergy and temperature rates for an instantonmediated decay channel. As the referee points out, an important question is whether this decay channel is the dominant one. We considered other decay channels, such as in section 3.4 where we consider decay via fragmentation. With regards to the specific concern of the decay of our black hole via Schwinger pair production, presumably of magnetic monopoles, we assume that the mass of such monopoles is sufficiently large that this decay channel is irrelevant. The decay rate is exponentially suppressed by the mass of the monopole, and heavy monopoles are confined by the effective radial potential.
We have added a new subsection, section 3.5, going into more detail on other decay channels.
 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.
The suggested reference discusses an enhancement of Hawking radiation of nearextremal magnetic black holes. In sec 5.1, we are working in the canonical ensemble, so the macrostate is in thermodynamic equilibrium. For the black hole phase, this means that emitted Hawking radiation, even if enhanced, is in equilibrium with incoming thermal radiation, so we do not believe that Maldacena’s enhancement result is of direct relevance to our work. The underlying reason is that in our setup the geometries we consider are asymptotically AdS, while Maldacena’s results are valid in asymptotically flat space.
We have added the reference and this comment to the new section 3.5.
References
[1] S. S. Gubser, “Breaking an Abelian gauge symmetry near a black hole horizon,” Phys. Rev. D 78 (2008) 065034, arXiv:0801.2977 [hepth]. [2] S. A. Hartnoll, C. P. Herzog, and G. T. Horowitz, “Building a Holographic Superconductor,” Phys. Rev. Lett. 101 (2008) 031601, arXiv:0803.3295 [hepth]. [3] S. A. Hartnoll, C. P. Herzog, and G. T. Horowitz, “Holographic Superconductors,” JHEP 12 (2008) 015, arXiv:0810.1563 [hepth]. [4] S.S. Lee, “A NonFermi Liquid from a Charged Black Hole: A Critical Fermi Ball,” Phys. Rev. D 79 (2009) 086006, arXiv:0809.3402 [hepth]. [5] H. Liu, J. McGreevy, and D. Vegh, “NonFermi liquids from holography,” Phys. Rev. D 83 (2011) 065029, arXiv:0903.2477 [hepth]. [6] M. Cubrovic, J. Zaanen, and K. Schalm, “String Theory, Quantum Phase Transitions and the Emergent FermiLiquid,” Science 325 (2009) 439–444, arXiv:0904.1993 [hepth]. [7] T. Faulkner, H. Liu, J. McGreevy, and D. Vegh, “Emergent quantum criticality, Fermi surfaces, and AdS(2),” Phys. Rev. D 83 (2011) 125002, arXiv:0907.2694 [hepth].
List of changes
Added a sentence in the third paragraph of the introduction to clarify the nonperturbative effect of gravity we probe: "In other words, we compute the nonperturbative, yet dominant decay rate between semiclassical solutions with different topologies."
Added a new section 3.5 on possible instabilities of the black hole phase such as Schwinger pair production and the enhancement of Hawking radiation of https://arxiv.org/abs/2004.06084.
Published as SciPost Phys. 16, 066 (2024)
Reports on this Submission
Weaknesses
There is perhaps too much emphasis on the possibility of test experimentally the result and simulations, but it is confined in the discussion session.
Report
The paper computes the tunneling rate from a pair of disconnected extremal black holes to a traversable wormhole. This is a nonperturbative effects of quantum gravity involving a change of topology. This is an interesting computation for understanding quantum gravity effects in holography. This timely paper is clear and wellwritten and, in my opinion, meets the criteria for publication in SciPost.