SciPost Submission Page
Asymptotic safety, quantum gravity, and the swampland: a conceptual assessment
by Ivano Basile, Benjamin Knorr, Alessia Platania, Marc Schiffer
Submission summary
| Authors (as registered SciPost users): | Benjamin Knorr · Alessia Platania |
| Submission information | |
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| Preprint Link: | https://arxiv.org/abs/2502.12290v2 (pdf) |
| Date submitted: | March 21, 2025, 4:29 p.m. |
| Submitted by: | Knorr, Benjamin |
| Submitted to: | SciPost Physics |
| Ontological classification | |
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| Academic field: | Physics |
| Specialties: |
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| Approach: | Theoretical |
Abstract
We provide a conceptual assessment of some aspects of fundamental quantum field theories of gravity in light of foundational aspects of the swampland program. On the one hand, asymptotically safe quantum gravity may provide a simple and predictive framework, thanks to a finite number of relevant parameters. On the other hand, a (sub-)set of intertwined swampland conjectures on the consistency of quantum gravity can be argued to be universal via effective field theory considerations. We answer whether some foundational features of these frameworks are compatible. This involves revisiting and refining several arguments (and loopholes) concerning the relation between field-theoretic descriptions of gravity and general swampland ideas. We identify the thermodynamics of black holes, spacetime topology change, and holography as the core aspects of this relation. We draw lessons on the features that a field theoretic description of gravity must (not) have to be consistent with fundamental principles underlying the swampland program, and on the universality of the latter.
Author indications on fulfilling journal expectations
- Provide a novel and synergetic link between different research areas.
- Open a new pathway in an existing or a new research direction, with clear potential for multi-pronged follow-up work
- Detail a groundbreaking theoretical/experimental/computational discovery
- Present a breakthrough on a previously-identified and long-standing research stumbling block
Current status:
Reports on this Submission
Strengths
2-thorough
3-extremely long list of references
Weaknesses
Report
I find the paper generally well argued, and want to especially commend the authors for their thorough review of the literature (which is much more thorough anyway than my knowledge of it). As an honest assessment of the substantial issues faced by field theoretic approaches to quantum gravity, it is a welcome addition to the efforts aimed at reconciling the various communities and potentially channeling their respective efforts on the most promising aspects. In view of this, my general tendency would be to recommend publication, provided the following two minor points are addressed.
Requested changes
First, it should be noted that the incompatibility with black hole thermodynamics has been the main objection from the string community to attempts at quantum gravity based on local field theory for almost three decades now. In particular, this objection predates and is completely independent of any landscape or swampland discussion. It would be worth emphasizing that the apparent difficulty of asymptotic safety to accommodate black hole entropy might point to a much more basic mathematical inconsistency of the theory. Relatedly, evading asymptotic darkness seems impossible without jeopardizing the validity of Einstein gravity (specifically, the formation of trapped surfaces) at long distances.
Second, I do not actually find the arguments in section 3.1 that exclude "spacetime topology change" internally entirely convincing. Again, a much more basic objection to asymptotic safety (or other local field theory approaches to quantum gravity) has been the incompatibility of local observables with diffeomorphism invariance. This is acknowledged later in the paper, where various loopholes are offered that might resolve this issue. It seems to me that if this is possible, then the same mechanism could also make these very observables "topology change invariant" much like in the context of the AdS/CFT correspondence asymptotic observables are well-defined because fluctuations of the metric and topology are confined to the interior. On a related note, I have never quite understood how the RG flow purported to lead to asymptotic safety should be compatible with diffeomorphism invariance, given that any scale or scale transformation is not. In any event, I would like to ask the authors to spell out more clearly their arguments on these points.
Recommendation
Ask for minor revision