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A Firewall Argument from the Swampland
by Himanshu Chaudhary, Chethan Krishnan
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Submission summary
| Authors (as registered SciPost users): | Chethan Krishnan |
| Submission information | |
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| Preprint Link: | https://arxiv.org/abs/2003.05488v1 (pdf) |
| Date submitted: | 2020-03-31 02:00 |
| Submitted by: | Krishnan, Chethan |
| Submitted to: | SciPost Physics |
| Ontological classification | |
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| Academic field: | Physics |
| Specialties: |
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| Approach: | Theoretical |
Abstract
A classical solution where the (scalar) field value moves by an ${\cal O}(1)$ range in Planck units is believed to signal the breakdown of Effective Field Theory (EFT). One heuristic argument for this is that such a field will have enough energy to be inside its own Schwarzschild radius, and will result in collapse. In this paper, we consider an inverse problem: what kind of field ranges arise during the gravitational collapse of a classical field? Despite the fact that collapse has been studied for almost a hundred years, most of the discussion is phrased in terms of fluid stress tensors, and not fields. An exception is the scalar collapse made famous by Choptuik. We re-consider Choptuik-like systems, but with the emphasis now on the evolution of the scalar. We give strong evidence that generic spherically symmetric collapse of a massless scalar field leads to super-Planckian field movement. This observation reveals a sharp tension between two pieces of received wisdom: the swampland ${\cal O}(1)$ field range bound, and the validity of EFT at the horizon (of an incipient black hole). We also discuss how the familiar perfect fluid models for collapse like Oppenheimer-Snyder and Vaidya should be viewed in light of our results, and note the relevance of our observation to the information paradox.
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Reports on this Submission
Report #1 by Anonymous (Referee 1) on 2020-7-8 (Invited Report)
- Cite as: Anonymous, Report on arXiv:2003.05488v1, delivered 2020-07-08, doi: 10.21468/SciPost.Report.1810
Report
The authors study the swampland distance conjecture in the context of gravitational collapse. By numerically solving Einstein's equations coupled to a scalar field, they construct the back-reacted solution for various initial configurations of the scalar field and demonstrate that the scalar field deviates by O(1) in Planck units at late times. The authors suggest that this leads to tension with the expected smoothness at the horizon of the incipient black hole, as the distance conjecture would signal a breakdown of effective field theory. The paper is well written, explains all the technical details clearly, and the results are of broad interest to the high energy theory community. I would therefore recommend publication of the article.
One thing I found a bit unclear is the location of point in spacetime at which the scalar field becomes large relative to the horizon of the incipient black hole. For instance, if this point were deep behind the horizon, then there would be no tension with the validity of EFT at the horizon. So it may be helpful (at least for pedagogical pursposes) to show the location of this point on a Penrose diagram, or demonstrate clearly that this point is indeed causally connected with asymptotic infinity.