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Topological black holes dressed with a conformally coupled scalar field and electric charge

High Energy Physics - Theory · Submitted 1 Dec 2005 · 62 references

Pith's verdict: A clean charged hairy AdS black hole with a non-area-law entropy and a tidy entropy-positivity/cosmic-censorship map, but the grand-canonical first law is never verified and my check suggests it may not hold for G ≠ 1.

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arXiv IDhep-th/0512022 (version 2)
Pith IDMXGL2U4C, Pith's permanent record of this paper and its review
CitationCristian Martinez, Juan Pablo Staforelli, Ricardo Troncoso. "Topological black holes dressed with a conformally coupled scalar field and electric charge." arXiv:hep-th/0512022 (2005). https://pith.science/paper/MXGL2U4C
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Referee report
The paper

The paper claims

An electrically charged black hole can carry a conformally coupled scalar field, and its entropy is not one quarter of the horizon area but that area divided by a scalar-dependent effective Newton constant, with the positivity bound on that

The reading

The paper asks whether a charged black hole can carry a conformally coupled scalar field — hair that the usual no-hair arguments discourage — while the scalar stays regular on and outside the horizon, and what that does to the hole's thermodynamics. Working in four dimensions with a negative cosmological constant and a horizon that is a surface of constant negative curvature, the authors exhibit an exact solution in which the scalar is real and smooth outside the horizon, and in which the charge-to-mass ratio is fixed by the couplings in the action rather than left free. The payoff is thermodynamic: because the scalar couples non-minimally to curvature, the entropy is not one quarter of the horizon area but one quarter of the area divided by an effective Newton constant $1/4$ ... more precisely $S = A_+/(4G_+)$ with $1/G_+ = (1/G)(1 - 4pi G phi_+^2/3)$ evaluated at the horizon. Requiring that entropy to be positive becomes a bound on the mass and charge, and after a conformal transformation to a frame where the scalar is minimally coupled, the same bound becomes the condition that the mapped spacetime has no naked singularity. If that correspondence holds, a purely thermodynamic requirement in one frame encodes a causal requirement in another.

What carries the argument

The load-bearing object is the effective Newton constant at the horizon, $1/G_+ = (1/G)(1 - 4pi G phi_+^2/3)$, which is precisely the conformal factor $hat{g}_{munu} = (1 - 4pi G phi^2/3) g_{munu}$ of the map to the Einstein frame, together with the field redefinition $Psi = sqrt{3/(4pi G)}, tanh^{-1}sqrt{4pi G/3}, phi$. Because the same combination of the scalar appears both as the thing that rescales the entropy and as the thing that decides where the conformal frame degenerates, the requirement $S > 0$ and the requirement that the Einstein-frame geometry not degenerate into a naked singularity are literally the same inequality. The Euclidean reduced action, with its boundary term fixed by the Regge-Teitelboim variation, is the technical vehicle that produces $S = A_+/(4G_+)$ from an on-shell action rather than by assumption.

Extended reading notes

Core claim

For the hyperbolic-horizon branch ($gamma = -1$, $Lambda = -3/l^2$) the metric $ds^2 = -[r^2/l^2 - (1 + Gmu/r)^2]dt^2 + [r^2/l^2 - (1 + Gmu/r)^2]^{-1}dr^2 + r^2 dsigma^2$, with scalar $phi = sqrt{1/(2alpha l^2)}, Gmu/(r + Gmu)$ and potential $A = -(q/r)dt$, solves the Einstein-Maxwell equations with a conformally coupled, quartically self-interacting scalar, subject to the constraint $q^2 = -gamma G mu^2 (1 + 2pi Lambda G/(9alpha))$ that ties charge to mass. The authors show the scalar is regular outside the horizon, that the mass may be negative but is bounded below ($Gmu ge -l/4$), and that in the negative-mass window the causal structure contains three horizons and describes a black hole inside a black hole, with a timelike scalar singularity that is nevertheless geometrically regular. Evaluating the Euclidean action in the grand canonical ensemble gives $M = sigma mu/4pi$, $Q = sigma q/4pi$ and the non-area-law entropy $S = A_+/(4G_+)$; positivity of that entropy yields a window on $mu$, and the paper argues that under the conformal map to the Einstein frame this same window is exactly the condition that the mapped solution is not a naked singularity. A companion $alpha = 0$ solution gives a massless charged hairy black hole with $r_+ = l$, $M = 0$ and $S = (sigma l^2/4)(1/G - q^2 l^2)$, whose positivity bound $Gq^2/l^2 < 1$ plays the same double role.

Load-bearing premise

The thermodynamics is read off from a formal variation of the boundary term, but the solution family is one-parameter — the constraint $q^2 = -gamma G mu^2 (1 + 2pi Lambda G/(9alpha))$ ties charge to mass — so temperature and potential cannot really be varied independently, and the paper never writes down or checks the first law $dM = T,dS + Phi,dQ$ along that constrained family.

Editorial extensions

If this is right

  • Charged, asymptotically locally AdS black holes with hyperbolic horizons exist in this theory alongside the Reissner-Nordstrom-AdS branch with the same boundary geometry, and the two branches meet only at vanishing mass and charge.
  • The entropy of a black hole with a non-minimally coupled scalar is a quarter of the horizon area measured in units of a scalar-dependent effective Newton constant, so the area law is recovered only in the limit where the scalar vanishes at the horizon.
  • Negative-mass black holes in this family have a causal structure with an inner and an outer event horizon, so a timelike observer can cross the outer horizon and still choose among several futures, including escaping to a mirror asymptotic region.
  • The $alpha = 0$ branch produces a massless, electrically charged hairy black hole with $r_+ = l$ whose entropy still depends on the stealth scalar through the effective Newton constant.
  • Bounds obtained from demanding positive entropy in the conformal frame coincide with bounds that forbid naked singularities in the minimally coupled Einstein frame.

Reading between the lines

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

  • The entropy formula suggests a general rule worth testing: whenever a scalar couples conformally, replace $G$ by $G_+$ at the horizon and the first law may still close, which would let one read off thermodynamic stability without redoing the Euclidean integral.
  • The 'black hole inside a black hole' causal structure raises a concrete question the paper sets aside: whether the inner horizon contributes an extra channel of Hawking radiation to asymptotic observers, which would make the single-horizon thermodynamic treatment an approximation rather than the full answer.
  • Because the conformal factor vanishes exactly where the effective Newton constant changes sign, the map between frames acts as a dictionary in which a negative-entropy solution is not merely unphysical but geometrically singular; this could be turned into a practical diagnostic for other conformally coupled hairy solutions.
  • The stealth solutions, whose stress-energy tensor vanishes while the scalar is nontrivial, suggest that scalar profiles can be invisible to the geometry but not to the entropy, a distinction worth checking in other dimensions.
Original abstract

Electrically charged solutions for gravity with a conformally coupled scalar field are found in four dimensions in the presence of a cosmological constant. If a quartic self-interaction term for the scalar field is considered, there is a solution describing an asymptotically locally AdS charged black hole dressed with a scalar field that is regular on and outside the event horizon, which is a surface of negative constant curvature. This black hole can have negative mass, which is bounded from below for the extremal case, and its causal structure shows that the solution describes a "black hole inside a black hole". The thermodynamics of the non-extremal black hole is analyzed in the grand canonical ensemble. The entropy does not follow the area, and there is an effective Newton constant which depends on the value of the scalar field at the horizon. If the base manifold is locally flat, the solution has no electric charge, and the scalar field has a vanishing stress-energy tensor so that it dresses a locally AdS spacetime with a nut at the origin. In the case of vanishing selfinteraction, the solutions also dress locally AdS spacetimes, and if the base manifold is of negative constant curvature a massless electrically charged hairy black hole is obtained. The thermodynamics of this black hole is also analyzed. It is found that the bounds for the black holes parameters in the conformal frame obtained from requiring the entropy to be positive are mapped into the ones that guarantee cosmic censorship in the Einstein frame.

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, 7,055 input tokens, $0.0003 reported.

What the abstract itself states, as probabilities: claims first 0.03 · states limitation 0.45 · human participants 0.01 · controlled comparison 0.02 · randomized assignment 0.01 · states quantitative result 0.32 · compares with prior results 0.12 · mentions code or data availability 0.01.

The abstract, sentence by sentence

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

Electrically charged solutions for gravity with a conformally coupled scalar field are found in four dimensions in the presence of a cosmological constant. If a quartic self-interaction term for the scalar field is considered, there is a solution describing an asymptotically locally AdS charged black hole dressed with a scalar field that is regular on and outside the event horizon, which is a surface of negative constant curvature. This black hole can have negative mass, which is bounded from below for the extremal case, and its causal structure shows that the solution describes a "black hole inside a black hole". The thermodynamics of the non-extremal black hole is analyzed in the grand canonical ensemble. The entropy does not follow the area, and there is an effective Newton constant which depends on the value of the scalar field at the horizon. If the base manifold is locally flat, the solution has no electric charge, and the scalar field has a vanishing stress-energy tensor so that it dresses a locally AdS spacetime with a nut at the origin. In the case of vanishing selfinteraction, the solutions also dress locally AdS spacetimes, and if the base manifold is of negative constant curvature a massless electrically charged hairy black hole is obtained. The thermodynamics of this black hole is also analyzed. It is found that the bounds for the black holes parameters in the conformal frame obtained from requiring the entropy to be positive are mapped into the ones that guarantee cosmic censorship in the Einstein frame.

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 Electrically charged solutions for gravity with a conformally coupled scalar field are found in four dimensions in the presence of a cosmological constant. contribution 0.54 0.91 0.14 asserted 1.00
s1 If a quartic self-interaction term for the scalar field is considered, there is a solution describing an asymptotically locally AdS charged black hole dressed with a scalar field that is regular on and outside the event horizon, which is a surface of negative constant curvature. result 0.85 0.88 0.26 asserted 0.98
s2 This black hole can have negative mass, which is bounded from below for the extremal case, and its causal structure shows that the solution describes a "black hole inside a black hole". result 0.92 0.88 0.21 asserted 0.77
s3 The thermodynamics of the non-extremal black hole is analyzed in the grand canonical ensemble. contribution 0.57 0.91 0.05 asserted 0.99
s4 The entropy does not follow the area, and there is an effective Newton constant which depends on the value of the scalar field at the horizon. result 1.00 0.88 0.11 asserted 1.00
s5 If the base manifold is locally flat, the solution has no electric charge, and the scalar field has a vanishing stress-energy tensor so that it dresses a locally AdS spacetime with a nut at the origin. result 0.99 0.86 0.05 asserted 1.00
s6 In the case of vanishing selfinteraction, the solutions also dress locally AdS spacetimes, and if the base manifold is of negative constant curvature a massless electrically charged hairy black hole is obtained. result 0.95 0.87 0.09 asserted 1.00
s7 The thermodynamics of this black hole is also analyzed. contribution 0.68 0.89 0.04 asserted 0.89
s8 It is found that the bounds for the black holes parameters in the conformal frame obtained from requiring the entropy to be positive are mapped into the ones that guarantee cosmic censorship in the Einstein frame. result 0.87 0.93 0.40 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
  • arXiv listing abstract v2
not examined
  • full text
  • figures and tables
  • references and citing sentences
  • relations to other papers
levels run
  • P abstract
not run
  • S sections
  • 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. FIG. 1: Penrose diagram for the generic case:
Figure 2. FIG. 2: Penrose diagram for

Figures reproduced from arXiv:hep-th/0512022 by the authors.

References
How the literature uses it

52 arXiv papers cite this in 105 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 · 68 sentences without a confident label

Builds on it 2 papers
  • We begin by considering the case of a conformally coupled scalar field, presenting the non-Abelian extension of the MTZ black hole [ref] .

    (Super-)renormalizable hairy meronic black holes · Discussion · 0.93

  • Par exemple, en utilisant les techniques d�crites dans ce chapitre, il est possible de construire en dimension quatre des trous noirs axioniques en th�orie d'Einstein-Maxwell-AdS en pr�sence d'un champ scalaire conform�ment coupl� � la gravitation et avec deux champs axioniques, conduisant ainsi � une axionisation des trous noirs de [ref] .

    Black hole solutions of modified gravity theories · Conclusion · 0.98

Uses its method or tool 1 paper
  • Here we observe a linear relation between temperature and heat capacity [equation] with the entropy for the MTZ black hole [equation] However, since the conformal coupling term appears in the action, the entropy should be obtained by making use of the Euclidean action approach [ref] and the Wald method [ref] as [equation] where an effective Newtonian constant at the event horizon is given by [equation] The positivity of entropy $S_M ≥0$ requires a bound [equation] It requires lower bounds for being the positive entropy.

    Holographic superconductor in the exact hairy black hole · CMTZ black holes · 0.84

Compares with it 8 papers
  • Les solutions que nous pr�sentons ici poss�dent un horizon plat, un cheveu scalaire secondaire et partagent des propri�t�s quasiment identiques � celles des trous noirs avec horizons hyperboliques �tudi�s dans [ref] .

    Black hole solutions of modified gravity theories · Introduction · 0.99

  • The causal structure of the solution is notoriously enhanced with respect to the MTZ family [ref] including regular black holes, wormholes and cosmological spacetimes with bounces[The vanishing cosmological constant case was early discussed in [ref] and it represents a traversable wormhole.].

    AdS-Taub-NUT spacetimes and exact black bounces with scalar hair · Introduction · 0.93

  • The temperature $T_H$ is identical to the Hawking temperature of the MTZ black hole as determined in [ref] .

    Hawking Radiation via Gravitational Anomalies in Non-spherical Topologies · Hawking Radiation from a TBH Conformally Coupled to a Scalar Field · 0.86

Cites it as background 21 papers
  • Fortunately, the charged MTZ (CMTZ) black hole was found with scalar hair when the coefficient $α$ of $ϕ^4$-term is between 0 and $2πG/3l^2$ [ref] , where the upper bound corresponds to the MTZ black hole [ref] and the lower bound is not allowed.

    Holographic superconductor in the exact hairy black hole · Introduction · 0.81

  • In particular, when gravitational theories are supplemented with conformally coupled scalar fields, a broad class of solutions has been constructed [ref] , including gravitational instantons [ref] .

    (Super-)renormalizable hairy meronic black holes · Introduction · 0.80

  • In the case of a negative cosmological constant, stable solutions were found numerically for spherical geometries [ref] and an exact solution in asymptotically AdS space with hyperbolic geometry was presented in [ref] and generalized later to include charge [ref] .

    A New Class of Exact Hairy Black Hole Solutions · Introduction · 0.93

Discussion

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