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Black holes and asymptotics of 2+1 gravity coupled to a scalar field

High Energy Physics - Theory · Submitted 22 Jan 2002 · 17 references

Pith's verdict: The asymptotic analysis and the hairy black hole family are solid and worth engaging; the printed temperature in (3.5) is wrong by a factor of Θ_ν², and the algebra argument is terse but the standard c-number logic holds.

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arXiv IDhep-th/0201170 (version 2)
Pith IDFRW6J7CP, Pith's permanent record of this paper and its review
CitationCristian Martinez, Jorge Zanelli, Marc Henneaux, Ricardo Troncoso. "Black holes and asymptotics of 2+1 gravity coupled to a scalar field." arXiv:hep-th/0201170 (2002). https://pith.science/paper/FRW6J7CP
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The paper

The paper claims

Three-dimensional gravity with a negative cosmological constant keeps its conformal asymptotic symmetry, and its central charge, even when a scalar field reaches infinity too slowly to count as localized matter.

The reading

The paper asks whether the asymptotic symmetry algebra of three-dimensional gravity with a negative cosmological constant survives when the matter coupled to it decays so slowly at infinity that it reaches the boundary instead of staying localized. The authors take a single self-interacting scalar field with falloff $gives$ — slower than the $r^{-(1+arepsilon)}$ decay that would make it invisible to the surface integrals — and show that the admitted asymptotic Killing vectors are still the two copies of the Virasoro algebra found for pure gravity, and that the canonical charges, once the scalar's contribution is added, still close with the same central charge $c = 3l/2G$. The payoff is a one-parameter family of exact, static, circularly symmetric black holes with scalar hair that is regular everywhere, whose causal structure matches the standard nonrotating black hole and which are continuously connected to the zero-mass solution. If the argument holds, the Brown-Henneaux central charge is not an artefact of vacuum boundary conditions but survives a class of matter backreaction that genuinely reaches infinity.

What carries the argument

Two pieces of machinery carry the argument. The first is the divergence cancellation between gravitational and scalar contributions to the canonical charge, computed with the Regge-Teitelboim surface-integral method: because the leading correction to $gives$ is tied to the scalar's leading coefficient $gives$, the $O(r)$ pieces of $gives$ and $gives$ cancel and leave a finite charge. The second is a conformal-frame construction: the potential family $gives$ is obtained by the rescaling $gives$ with $gives$ and $gives$ from an action whose matter part is conformally invariant for every value of the parameter $gives$, which is what makes the exact hairy solutions tractable. The horizon radius is read off as the first zero of the Schuster function $gives$, and consistency of the boundary conditions with the field equations is claimed to force the potential into the form $gives$ with $gives$ an arbitrary smooth function.

Extended reading notes

Core claim

The paper's central claim is that the asymptotic conditions $gives$, $gives$ and $gives$ — in which the radial metric component falls off one power of $r$ more slowly than in pure gravity — are left invariant by exactly the same asymptotic Killing vectors that generate the conformal group in the vacuum theory. The reason the symmetry survives is a cancellation: the variation of the scalar charge $gives$ contains a term linear in $r$ that would diverge, and it is cancelled by a divergent piece of the gravitational charge $gives$ precisely because, to leading order, $gives$. The total charge $gives$ is then finite, and the algebra of canonical generators is stated to be two copies of the Virasoro algebra with the same central extension as in pure gravity, since the vacuum is taken to be the standard massless black hole and the central-charge computation is therefore identical. On top of this, the authors exhibit exact black hole solutions with regular scalar hair for the potential family $gives$, with horizon at $gives$, mass $gives$, temperature $gives$, and entropy $S = A/4$; the specific heat equals the entropy, exactly as for the standard black hole. The authors themselves flag one loose end: applying Cardy's formula to the unchanged central charge would give an entropy larger than $A/4$ for $gives$, which they leave unresolved.

Load-bearing premise

The central-charge argument assumes that the reference configuration for this slower-falloff class is the standard massless black hole with vanishing scalar field, even though the same class also contains the $gives$ metric that the paper itself calls a degenerate ground state, and the paper does not show that these two are the same state or that the central charge is independent of which one is used as the reference.

Editorial extensions

If this is right

  • The Brown-Henneaux central charge $c = 3l/2G$ applies to a boundary-condition class in which the matter stress tensor does not vanish at infinity, so the correspondence between 2+1 gravity and a boundary conformal theory is not restricted to localized matter.
  • For every $gives$ there is an explicit hairy black hole with $gives$, $gives$ and $gives$, so the thermodynamic identities of the standard black hole carry over to the dressed solutions unchanged, including the equality of specific heat and entropy.
  • Because there is only one integration constant $B$, fixing the mass fixes the scalar profile: the scalar cannot be switched off at fixed mass, so each mass admits two distinct black holes, one with $gives$ and one with nontrivial hair.
  • The limit $gives$ gives a configuration of vanishing mass, temperature and entropy, which the paper treats as a degenerate ground state continuously connected to the rest of the family.
  • Consistency of the asymptotic conditions with the field equations restricts the admissible self-interactions to the family $gives$, so only a specific class of scalar potentials supports this slow-falloff behavior.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • If the central charge really is a property of the asymptotic class rather than of the chosen reference configuration, the same argument should extend to other matter that reaches the boundary slowly, such as gauge fields with logarithmic falloff or dilatonic couplings, which would turn this into a general statement about non-normalizable matter in AdS$_3$.
  • The acknowledged mismatch between Cardy counting and the area law may be a signal that the Cardy formula should be applied to the $gives$ configuration rather than the standard massless black hole, or with a shifted zero-point energy; checking which choice reproduces $S = A/4$ would identify the state the boundary theory actually counts.
  • The paper's charge formula already carries a rotational term $gives$, so a rotating generalization of the hairy family is a natural next check; if rotation preserves the same central extension, the robustness claim is strengthened considerably.
  • Because $gives$ interpolates between a previously known solution at $gives$ and the degenerate ground state at $gives$, the family looks like a continuous deformation of the dual theory, which could be probed by computing quasi-normal mode frequencies as a function of $gives$.
Original abstract

We consider 2+1 gravity minimally coupled to a self-interacting scalar field. The case in which the fall-off of the fields at infinity is slower than that of a localized distribution of matter is analyzed. It is found that the asymptotic symmetry group remains the same as in pure gravity (i.e., the conformal group). The generators of the asymptotic symmetries, however, acquire a contribution from the scalar field, but the algebra of the canonical generators possesses the standard central extension. In this context, new massive black hole solutions with a regular scalar field are found for a one-parameter family of potentials. These black holes are continuously connected to the standard zero mass black hole.

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.

Compiled by classifier-1.13-20260917 via OpenRouter, question bank abstract-p1-20260923, 2026-09-23: 1 request, 4,824 input tokens, $0.0002 reported.

What the abstract itself states, as probabilities: claims first 0.03 · states limitation 0.14 · human participants 0.01 · controlled comparison 0.14 · randomized assignment 0.01 · states quantitative result 0.18 · compares with prior results 0.75 · mentions code or data availability 0.01.

The abstract, sentence by sentence

arXiv listing abstract v2. Results and the main claim are underlined; .

We consider 2+1 gravity minimally coupled to a self-interacting scalar field. The case in which the fall-off of the fields at infinity is slower than that of a localized distribution of matter is analyzed. It is found that the asymptotic symmetry group remains the same as in pure gravity (i.e., the conformal group). The generators of the asymptotic symmetries, however, acquire a contribution from the scalar field, but the algebra of the canonical generators possesses the standard central extension. In this context, new massive black hole solutions with a regular scalar field are found for a one-parameter family of potentials. These black holes are continuously connected to the standard zero mass black hole.

background contribution method result interpretation main claim

What the classifier reports for each sentence. The number is the probability it gave the label.
#sentencerolethe authors' own workstates the main conclusionstrength
s0 We consider 2+1 gravity minimally coupled to a self-interacting scalar field. contribution 0.57 0.66 0.03 asserted 0.89
s1 The case in which the fall-off of the fields at infinity is slower than that of a localized distribution of matter is analyzed. contribution 0.90 0.63 0.04 asserted 0.86
s2 It is found that the asymptotic symmetry group remains the same as in pure gravity (i.e., the conformal group). result 1.00 0.91 0.28 asserted 1.00
s3 The generators of the asymptotic symmetries, however, acquire a contribution from the scalar field, but the algebra of the canonical generators possesses the standard central extension. result 1.00 0.90 0.22 asserted 1.00
s4 In this context, new massive black hole solutions with a regular scalar field are found for a one-parameter family of potentials. result 0.98 0.96 0.31 asserted 1.00
s5 These black holes are continuously connected to the standard zero mass black hole. result 0.98 0.86 0.14 asserted 1.00

What kind of paper the classifier reports this is: theoretical result 1.00 · evidence from proof or derivation 1.00.

What was examined, and what was not

sources read
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  • references and citing sentences
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  • T body sentences
  • C citations
  • R cross-paper relations

Every quoted sentence on this record is the authors'. Every label is from Pith's closed vocabulary, with the probability shown beside it. Every number in the measurements table is the authors', checked by code. Record as JSON

Figures
Figure 1. Plot of Θν as a function of ν. The intercepts are at Θ−1 = 0 and Θ0 = 4 3 . where B is a non-negative integration constant and H(r) = 1 2  r + p r 2 + 4Br . The line element reads ds2 = −  H H + B 2 F(r)dt2 +  H + B H + 2B 2 dr2 F(r) + r 2 dϕ2 , (3.4) with F = H2 l 2 − (1 + ν)  3B2 l 2 + 2B3 l 2H  . The causal structure of this geometry is the same as for the standard, nonrotating 2+ 1 black hole. The event horizon is located at r+ = BΘν , where the constant Θν is the first zero of the Schuster function of order ν, given by [12] Θν = 2(zz¯) 2/3 z 2/3 − z¯ 2/3 z − z¯ , and z…

Figures reproduced from arXiv:hep-th/0201170 by the authors.

References
How the literature uses it

47 arXiv papers cite this in 96 sentences

Each citing sentence is taken from the citing paper's LaTeX source and typed by Pith's classifier. A label appears at probability 0.8 or more (0.95 for support), a contest at 0.7 or more; the quoted words are the citing authors'. How each label was checked · JSON

Papers citing it · 66 sentences without a confident label

Builds on it 1 paper
  • Thus, if one considers the static hairy black hole of Ref. [ref] [equation] which has the same scalar field given in ([ref]), and performs the following boost [equation] where the constant $ω$ is restricted to satisfy $ω^2<1$, one directly obtains the rotating hairy solution described by Eqs. ([ref])-([ref]).

    Rotating hairy black hole and its microscopic entropy in three spacetime dimensions · Rotating hairy scalar black hole in three dimensions · 0.95

Uses its method or tool 1 paper
Compares with it 3 papers
Cites it as background 23 papers

Discussion

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