REVIEW
Holographic Renormalization of Asymptotically Flat Spacetimes
High Energy Physics - Theory · Submitted 8 Nov 2005 · 59 references
Pith's verdict: A genuinely new implicit counter-term that gives a finite, stationary action for asymptotically flat gravity, with one honest caveat in d=4 that the abstract papers over.
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Referee report
The paper
The paper claims
A local boundary term gives asymptotically flat gravity a finite, stationary action, and charges that include NUT.
The reading
What carries the argument
The central object is $K_{ij}$, the trace-reversed analogue of the extrinsic curvature the boundary would have if it were detached from the bulk and embedded in Minkowski space. Instead of solving the full Gauss-Codazzi relation, which has too many components to admit a solution when the boundary has more than three dimensions, the authors use only its trace, $R_{ik} = K_{ik}K - K^{m}{}_{i}K_{mk}$, and solve that for a symmetric tensor. This makes the counter-term a local algebraic function of the boundary metric and its Ricci tensor, and it is what distinguishes the construction from the reference-background subtraction it imitates: background subtraction needs an embedding to exist for an open set of boundary metrics, which fails for $d$ at least 4. The finiteness argument is power counting: the difference between the true extrinsic curvature and the counter-term tensor is sourced by the bulk Riemann tensor, giving a difference of order $O(1)$ in the trace for cylindrical temporal cutoffs, and for hyperbolic cutoffs the leading correction is the electric part of the Weyl tensor, which is traceless, so the trace difference is one power of the radius smaller still. The stationarity argument linearises the same defining equation and shows the resulting boundary momentum matches the true one to the required order. The charge construction then follows a general counter-term charge prescription, with a boundary stress tensor whose leading piece is proportional to the electric Weyl tensor.
Extended reading notes
Core claim
The paper's claim is that the action $S_{renorm} = S_{EH+GH} + (1/8G)$ times the integral over the boundary of the square root of the boundary metric times the trace of a tensor $K_{ij}$ (defined implicitly, see key machinery) has two properties: it is finite on asymptotically flat Ricci-flat solutions, and it is stationary about any such solution under all variations that preserve asymptotic flatness. Both properties are argued for any dimension $d$ at least 4, for a cylindrical temporal cutoff combined with either a cylindrical or a hyperbolic spatial cutoff, and for a hyperbolic temporal cutoff combined with a hyperbolic spatial cutoff, with one qualification: in $d=4$ with the hyperbolic temporal cutoff the variations must be restricted to those with $h_{1ij}$ changing as a multiple of the leading boundary metric, a condition taken over from Ashtekar, Bombelli and Reula. The paper also checks two earlier proposals, a counter-term proportional to the square root of the boundary Ricci scalar and the Kraus-Larsen-Siebelink counter-term, and finds them finite and stationary for $d$ at least 5 with these cutoffs, but shows by explicit next-order calculation that the square-root counter-term is not in general stationary in $d=4$ with hyperbolic cutoffs. Finally, the same actions feed the counter-term charge algorithm to produce finite conserved quantities at spacelike infinity; these agree with standard ADM-type definitions where those are defined, and extend them to cases with large magnetic Weyl part.
Load-bearing premise
The implicit equation defining the counter-term tensor must have a solution over an open set of boundary metrics near spacelike infinity, so that the term is defined not just on one solution but on all nearby ones that the action must be varied through.
Editorial extensions
If this is right
- A finite, stationary action for asymptotically flat vacuum gravity in any dimension $d$ at least 4, for cylindrical and hyperbolic cutoffs, closing a gap between flat-space and anti-de Sitter treatments of the gravitational path integral.
- Conserved energy, momentum and angular momentum at spacelike infinity follow from a single algorithm rather than case-by-case surface-term constructions, and agree with ADM values where those exist.
- The same charges extend to spacetimes whose magnetic Weyl part is as large as the electric part, giving well-defined charges for non-zero NUT charge in four dimensions.
- The failure of the square-root-Ricci-scalar counter-term in four dimensions with hyperbolic cutoffs shows that matching only the leading divergence is not enough; sub-leading structure of the counter-term matters.
- A boundary stress tensor at spacelike infinity whose leading term is the electric Weyl tensor, conserved at every finite cutoff, mirroring the anti-de Sitter boundary stress tensor story.
Reading between the lines
- Because the counter-term is built only from the boundary Ricci tensor and its trace, the construction looks portable to actions with matter or higher-curvature bulk terms, provided the near-infinity falloff of the extra fields is slow enough to be absorbed into the same power counting.
- The conserved charges being expressible as an integral of a boundary stress tensor contracted with an asymptotic Killing field suggests a dual description living at spacelike infinity with a stress tensor whose leading piece is traceless; whether such a dual is a local field theory is not addressed and seems doubtful given the de Sitter-like signature of the boundary.
- The four-dimensional hyperbolic-cutoff restriction on variations is exactly the kind of condition that a covariant phase space with finite symplectic structure imposes; a reader could test whether the restricted variations are the full set compatible with finite symplectic flux, or merely a sufficient subset.
- The paper leaves past and future boundary terms uncomputed throughout, so any application with corners, such as the Euclidean thermal case the authors mention, would need those terms checked before the numerical value of the action could be trusted.
Original abstract
A new local, covariant ``counter-term'' is used to construct a variational principle for asymptotically flat spacetimes in any spacetime dimension $ d \ge 4$. The new counter-term makes direct contact with more familiar background subtraction procedures, but is a local algebraic function of the boundary metric and Ricci curvature. The corresponding action satisfies two important properties required for a proper treatment of semi-classical issues and, in particular, to connect with any dual non-gravitational description of asymptotically flat space. These properties are that 1) the action is finite on-shell and 2) asymptotically flat solutions are stationary points under {\it all} variations preserving asymptotic flatness; i.e., not just under variations of compact support. Our definition of asymptotic flatness is sufficiently general to allow the magentic part of the Weyl tensor to be of the same order as the electric part and thus, for d=4, to have non-vanishing NUT charge. Definitive results are demonstrated when the boundary is either a cylindrical or a hyperbolic (i.e., de Sitter space) representation of spacelike infinity ($i^0$), and partial results are provided for more general representations of $i^0$. For the cylindrical or hyperbolic representations of $i^0$, similar results are also shown to hold for both a counter-term proportional to the square-root of the boundary Ricci scalar and for a more complicated counter-term suggested previously by Kraus, Larsen, and Siebelink. Finally, we show that such actions lead, via a straightforward computation, to conserved quantities at spacelike infinity which agree with, but are more general than, the usual (e.g., ADM) results.
The compiled record
The paper's own sentences, arranged, kept beside the review and separate from it. Each label is drawn from a closed vocabulary; the number beside it is the probability the classifier gave that label. Numbers in the tables are the authors', checked by code. No sentence in this record was written by a model.
The abstract, sentence by sentence
A new local, covariant ``counter-term'' is used to construct a variational principle for asymptotically flat spacetimes in any spacetime dimension $ d \ge 4$. The new counter-term makes direct contact with more familiar background subtraction procedures, but is a local algebraic function of the boundary metric and Ricci curvature. The corresponding action satisfies two important properties required for a proper treatment of semi-classical issues and, in particular, to connect with any dual non-gravitational description of asymptotically flat space. These properties are that 1) the action is finite on-shell and 2) asymptotically flat solutions are stationary points under {\it all} variations preserving asymptotic flatness; i.e., not just under variations of compact support. Our definition of asymptotic flatness is sufficiently general to allow the magentic part of the Weyl tensor to be of the same order as the electric part and thus, for d=4, to have non-vanishing NUT charge. Definitive results are demonstrated when the boundary is either a cylindrical or a hyperbolic (i.e., de Sitter space) representation of spacelike infinity ($i^0$), and partial results are provided for more general representations of $i^0$. For the cylindrical or hyperbolic representations of $i^0$, similar results are also shown to hold for both a counter-term proportional to the square-root of the boundary Ricci scalar and for a more complicated counter-term suggested previously by Kraus, Larsen, and Siebelink. Finally, we show that such actions lead, via a straightforward computation, to conserved quantities at spacelike infinity which agree with, but are more general than, the usual (e.g., ADM) results.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | A new local, covariant ``counter-term'' is used to construct a variational principle for asymptotically flat spacetimes in any spacetime dimension $ d \ge 4$. | contribution 0.98 | 0.93 | 0.37 | asserted 1.00 |
| s1 | The new counter-term makes direct contact with more familiar background subtraction procedures, but is a local algebraic function of the boundary metric and Ricci curvature. | contribution 0.45 | 0.78 | 0.09 | asserted 1.00 |
| s2 | The corresponding action satisfies two important properties required for a proper treatment of semi-classical issues and, in particular, to connect with any dual non-gravitational description of asymptotically flat space. | result 0.66 | 0.77 | 0.17 | asserted 1.00 |
| s3 | These properties are that 1) the action is finite on-shell and 2) asymptotically flat solutions are stationary points under {\it all} variations preserving asymptotic flatness; i.e., not just under variations of compact support. | result 0.80 | 0.77 | 0.21 | asserted 0.99 |
| s4 | Our definition of asymptotic flatness is sufficiently general to allow the magentic part of the Weyl tensor to be of the same order as the electric part and thus, for d=4, to have non-vanishing NUT charge. | contribution 0.54 | 0.65 | 0.05 | asserted 0.92 |
| s5 | Definitive results are demonstrated when the boundary is either a cylindrical or a hyperbolic (i.e., de Sitter space) representation of spacelike infinity ($i^0$), and partial results are provided for more general representations of $i^0$. | limitation 0.38 | 0.90 | 0.10 | asserted 1.00 |
| s6 | For the cylindrical or hyperbolic representations of $i^0$, similar results are also shown to hold for both a counter-term proportional to the square-root of the boundary Ricci scalar and for a more complicated counter-term suggested previously by Kraus, Larsen, and Siebelink. | result 0.95 | 0.87 | 0.08 | asserted 1.00 |
| s7 | Finally, we show that such actions lead, via a straightforward computation, to conserved quantities at spacelike infinity which agree with, but are more general than, the usual (e.g., ADM) results. | result 1.00 | 0.95 | 0.35 | asserted 1.00 |
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References
How later papers used it
76 later papers cite it
3 later papers by other authors are listed below: 1 built on it and 2 used its method or tool. 1 more paper by the same authors is listed: 1 used its method or tool.
Builds on it 1 of 7 papers with this label
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Said that its result generalizes this paper's previous result, where variations over asymptotically flat configurations with only fixed magnetic four-momentum were considered with hyperbolic temporal and spatial cut-offs.
Asymptotic Flatness, Taub-NUT, and Variational Principle (2011) · 0.97 · paraphrased: the licence does not allow quoting
Uses its method or tool 3 of 13 papers with this label · 1 by the same authors
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Used an intrinsic boundary quantity defined implicitly by the relation given in this paper in its action.
Celestial IR divergences and the effective action of supertranslation modes (2021) · 0.80 · paraphrased: the licence does not allow quoting
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Evaluated the boundary stress-tensor using the formula from this paper to compute the conserved charges.
Harrison transformation and charged black objects in Kaluza-Klein theory (2009) · 0.99 · paraphrased: the licence does not allow quoting
By the same authors
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Followed the same approach that was used in this paper.
Boundary Terms Unbound! Holographic Renormalization of Asymptotically Linear Dilaton Gravity (2009) (same authors) · 1.00 · paraphrased: the licence does not allow quoting
How the literature uses it
70 arXiv papers cite this in 178 sentences
Papers citing it · 110 sentences without a confident label
Contests it 1 paper
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The primary purpose of this paper is to address the terms in the stress tensor that were overlooked in [ref] .
On the Stress Tensor for Asymptotically Flat Gravity · Introduction · contest 0.85
Builds on it 6 papers
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This generalizes the previous result [ref] where with hyperbolic temporal and spatial cut-offs variations over asymptotically flat configurations with only fixed magnetic four-momentum, i.e., $δk_ab = 0$, were considered.
Asymptotic Flatness, Taub-NUT, and Variational Principle · Conclusions · 0.97
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In this section we generalize the constructions of [ref] to the ALD theories described in the last section.
Boundary Terms Unbound! Holographic Renormalization of Asymptotically Linear Dilaton Gravity · $$ Counterterms · 0.99
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First, we further elaborate on the discussion of [ref] on how the six Lorentz charges are encoded at the boundary in the form of conserved tensors.
On Asymptotic Flatness and Lorentz Charges · Introduction and Summary of Results · 0.95
Uses its method or tool 13 papers
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We then present the covariant counterterm action of [ref] in section [ref], and vary it with respect to the boundary metric to obtain the full boundary stress tensor.
On the Stress Tensor for Asymptotically Flat Gravity · Introduction · 0.81
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We adopt those of Compère and Dehouck [ref] which are less restrictive than all other boundary conditions previously considered in the literature, [equation] On the resulting restricted phase-space, a suitable action to consider is [ref] [equation] where $S_EH$ denotes the standard Einstein–Hilbert action [equation] and $S_ℋ_+$ is the sum of the Gibbons–Hawking–York (GHY) and Mann–Marolf (MM) countertems required to make the variational principle well-posed at the spatial boundaries, [equation] Here, $K$ is the extrinsic curvature while $K̂=H^abK̂_ab$ is an intrinsic boundary quantity defined implicitly[Although we will not make use of them, explicit formulas for $K̂_ab$ are also available [ref] .] by the relation [ref] [equation] where $R_ab[H]$ is the Ricci tensor constructed from the induced metric $H_ab$.
Celestial IR divergences and the effective action of supertranslation modes · Gravity at spatial infinity · 0.80
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We perform this analysis in the covariant phase space approach of [ref] as well as in the holographic renormalization approach of Mann and Marolf [ref] .
Supertranslations and Holographic Stress Tensor · Introduction · 1.00
Compares with it 3 papers
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This is not a surprising result: gravity with asymptotically flat boundary conditions suffers from the same problem [ref] .
Boundary Terms Unbound! Holographic Renormalization of Asymptotically Linear Dilaton Gravity · Equations of Motion · 0.84
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The advantage of the first order treatment is that, unlike [ref] , the surface term is given explicitly and there are no infinite counter-terms involved.
The gravitational Hamiltonian, first order action, Poincar\'e charges and surface terms · Introduction · 0.99
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This is in contrast to previous works that, in analogy with the AdS case, studied holography at various boundaries of flat space [ref] .
Mapping AdS to dS spaces and back · Introduction · 0.96
Cites it as support 2 papers
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Even if the regulating boundary for a spacetime can be embedded in an appropriate reference background, such embeddings cannot be constructed for an open family around that spacetime [ref] .
Boundary Terms Unbound! Holographic Renormalization of Asymptotically Linear Dilaton Gravity · Introduction · 1.00
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For this reason, the variational principle associated to the renormalized gravitational action ([ref]) is not always well-defined [ref] .
Spin Connection and Renormalization of Teleparallel Action · Introduction · 0.98
Cites it as background 27 papers
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More recently, a definition of conserved charges was introduced that makes use of a boundary stress tensor [ref] .
On the Stress Tensor for Asymptotically Flat Gravity · Introduction · 0.87
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The AdS/CFT correspondence [ref] has been brought up for long time while there are lots of attempts [ref] aiming to construct the duality relation between the quantum gravity theory with (asymptotically) flat background and the boundary conformal field theories.
Holographic reconstruction of flat spacetime · Introduction · 0.98
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The total gravitational action [ref] then depends on both the spacetime and reference metrics and can be written as [ref] [equation] The well-known problem is that the isometric embedding of a metric in Minkowski spacetime does not have to exist, what lead to development of new regularization methods, including holographic renormalization, where the counterterm is a local covariant function of the intrinsic geometry of the boundary [ref] , and the recent counterterm for null boundaries [ref] .
Einstein gravity from the Einstein action: Counterterms and covariance · Introduction · 0.85
Discussion
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