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Black holes with unusual topology

General Relativity and Quantum Cosmology · Submitted 5 May 1997 · 41 references

Pith's verdict: A careful, honest thermodynamics paper: the S = A/4 fix for higher-genus AdS black holes is real but rests on a background choice the paper argues for rather than derives.

T0 · AI review

How this review was made: An AI referee (selfhosted/deepseek-v4.1-flash) read the paper on November 11, 2026 and answered a fixed list of questions about it. T0 is the starting level every paper gets. The levels describe how deeply Pith has checked the paper, never the authors.

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  5. T4 Proof Those claims proved, and the proof checked by computer.

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arXiv IDgr-qc/9705004 (version 3)
Pith IDZCK6LMDM, Pith's permanent record of this paper and its review
CitationL. Vanzo. "Black holes with unusual topology." arXiv:gr-qc/9705004 (1997). https://pith.science/paper/ZCK6LMDM
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Referee report
The paper

The paper claims

Black holes in anti-de Sitter space can have horizons shaped like tori or higher-genus Riemann surfaces, and their thermodynamics becomes well behaved — positive mass, entropy equal to one quarter the horizon area — once the zero of energy,

The reading

Einstein's equations with a negative cosmological constant do not force a black hole horizon to be a sphere. Vanzo shows that the standard static ansatz $ds^2=-V dt^2+V^{-1}dr^2+r^2 dsigma^2$ still solves the equations when the two-surface carrying $dsigma^2$ has constant curvature of either sign, so the horizon can be a torus or a Riemann surface of any genus $g>1$. Each such solution has a horizon radius, a surface gravity, and a temperature fixed by the period of the Euclidean continuation, and a mass defined by Hamiltonian subtraction against a reference solution of the same topology. The paper's real target is a bookkeeping problem: with the natural subtraction (the zero-mass, locally anti-de Sitter solution) the higher-genus entropy picks up a negative topological term and goes negative at low temperature, which is nonsense. Vanzo argues that subtracting instead the extreme solution — the one whose Euclidean section is regular at any period — removes the term and leaves $S=A/4$ with a non-negative mass spectrum.

What carries the argument

The load-bearing object is the lapse function $V=kappa-k'/r+r^2/ell^2$, which satisfies $R_{ab}=Lambda g_{ab}$ with $Lambda=-3ell^{-2}$ for any constant-curvature two-metric $sigma_{ij}$ with $R_{ij}=kappa,sigma_{ij}$. Rescaling sets $kappa=-1$ for $g>1$ and $kappa=0$ for the torus, giving $V=-1-2eta/r+r^2/ell^2$ and $V=-2eta/r+r^2/ell^2$ respectively, with the horizon at the positive root $r_+$. The temperature comes from requiring the Euclidean section to close smoothly at $r_+$: $beta_+=4piell^2 r_+/(3r_+^2-ell^2)$ for $g>1$ and $beta_+=4piell^2/(3r_+)$ for the torus. The mass comes from the Hamiltonian boundary term $-frac{1}{8pi}int_{S_g}sqrt{V}(Theta-Theta_0),r^2sqrt{sigma},d^2x$ evaluated at large radius, which forces the background to carry the same genus as the solution. The entropy comes from the off-shell Euclidean action with the Gauss-Bonnet conical-defect contribution $frac{A}{16pi}frac{beta_+}{beta}(beta_+-beta)$ for both solution and background.

Extended reading notes

Core claim

The central claim is that the whole family of topological anti-de Sitter black holes, from the torus up through every genus, forms a thermodynamically consistent sequence once the reference background used to define energy is chosen to be the extreme solution with $eta_0=-ell/(3sqrt{3})$ (equivalently $r_0=r_c=ell/sqrt{3}$). The mass formula $M=(eta-eta_0)(g-1)+eta|mathrm{Im},tau|,delta(g,1)/(4pi)$ ties the mass to the horizon geometry, the first law $dM=kappa,dA/8pi$ holds for every genus, and the off-shell Euclidean action $I=beta M-A/4+[1-delta(r_0,r_c)]A_0/4$ reproduces both the mean energy and the entropy. With the extreme background the indicator factor $[1-delta(r_0,r_c)]$ switches off, the conical contribution of the background disappears, and the entropy reduces to exactly one quarter of the horizon area, $S=A/4-pi r_0^2(g-1)[1-delta(r_0,r_c)]$. The author reads this as evidence that the negative-mass and negative-entropy branches found under the other subtraction were an artifact of the wrong zero of energy, and that the third law of thermodynamics lines up with the third law of black hole mechanics: the zero-temperature state is the extreme solution, which is a naked singularity rather than a black hole.

Load-bearing premise

The argument rests on treating the extreme solution — the one whose Euclidean section stays regular at any imaginary-time period — as the physically correct zero of energy, a choice the paper defends by regularity and by the disappearance of a negative entropy term rather than by deriving it from the dynamics; the author concedes there is freedom in where the zero of energy is placed.

Editorial extensions

If this is right

  • For every genus $g$, the first law $dM=kappa,dA/8pi$ holds in vacuum, and the mass is a monotonically increasing function of temperature, so the specific heat is positive and the canonical ensemble is stable.
  • The toroidal black hole has $r_+=(8piell^2M/|mathrm{Im},tau|)^{1/3}$, so its size is set by the mass and the torus's conformal class rather than by the cosmological constant; small toroidal black holes can exist at any mass.
  • Higher-genus black holes have no small-mass limit: their minimum size is of order $ell$, so they are cosmological objects that could only have existed when the cosmological constant was large.
  • The density of states grows as $rho(E)simexp(C_1E^{2/3})$ with exponent fixed by $A/4$, matching the behaviour of a massless gas in two spatial dimensions.
  • The genus, and for the torus the Teichmüller parameter $tau$, enter the metric as free non-dynamical parameters, so the spectrum contains disconnected sectors labelled by horizon topology.

Reading between the lines

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

  • If the entropy really is $A/4$ independent of subtraction, then the negative-entropy branch is a diagnostic of a bad reference frame rather than a physical instability, which suggests a general rule: any candidate zero of energy whose Euclidean section is not regular at arbitrary period should be suspect in anti-de Sitter thermodynamics.
  • The genus label behaving as a fixed external parameter is the sharpest loose end; a path-integral treatment that sums over horizon topologies would turn it into a dynamical variable and could in principle allow transitions between genus sectors, which the paper explicitly says it cannot rule out.
  • The same subtraction ambiguity should show up in the charged topological black holes, where an inner horizon gives a second natural candidate for the zero of energy; checking whether the extreme charged solution plays the same regularizing role would test whether the mechanism is about extremality rather than about this particular uncharged family.
  • Because the toroidal solution survives in a nearly flat universe while higher-genus ones do not, the observable content of this family is concentrated in the $g=1$ case, which makes the torus's conformal class the one free parameter worth asking about physically.
Original abstract

The Einstein's equations with a negative cosmological constant admit solutions which are asymptotically anti-de Sitter space. Matter fields in anti-de Sitter space can be in stable equilibrium even if the potential energy is unbounded from below, violating the weak energy condition. Hence there is no fundamental reason that black hole's horizons should have spherical topology. In anti-de Sitter space the Einstein's equations admit black hole solutions where the horizon can be a Riemann surface with genus $g$. The case $g=0$ is the asymptotically anti-de Sitter black hole first studied by Hawking-Page, which has spherical topology. The genus one black hole has a new free parameter entering the metric, the conformal class to which the torus belongs. The genus $g>1$ black hole has no other free parameters apart from the mass and the charge. All such black holes exhibits a natural temperature which is identified as the period of the Euclidean continuation and there is a mass formula connecting the mass with the surface gravity and the horizon area of the black hole. The Euclidean action and entropy are computed and used to argue that the mass spectrum of states is positive definite.

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, 6,851 input tokens, $0.0003 reported.

What the abstract itself states, as probabilities: claims first 0.14 · states limitation 0.09 · human participants 0.01 · controlled comparison 0.03 · randomized assignment 0.01 · states quantitative result 0.29 · compares with prior results 0.61 · mentions code or data availability 0.01.

The abstract, sentence by sentence

arXiv listing abstract v3. Results and the main claim are underlined; .

The Einstein's equations with a negative cosmological constant admit solutions which are asymptotically anti-de Sitter space. Matter fields in anti-de Sitter space can be in stable equilibrium even if the potential energy is unbounded from below, violating the weak energy condition. Hence there is no fundamental reason that black hole's horizons should have spherical topology. In anti-de Sitter space the Einstein's equations admit black hole solutions where the horizon can be a Riemann surface with genus $g$. The case $g=0$ is the asymptotically anti-de Sitter black hole first studied by Hawking-Page, which has spherical topology. The genus one black hole has a new free parameter entering the metric, the conformal class to which the torus belongs. The genus $g>1$ black hole has no other free parameters apart from the mass and the charge. All such black holes exhibits a natural temperature which is identified as the period of the Euclidean continuation and there is a mass formula connecting the mass with the surface gravity and the horizon area of the black hole. The Euclidean action and entropy are computed and used to argue that the mass spectrum of states is positive definite.

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 The Einstein's equations with a negative cosmological constant admit solutions which are asymptotically anti-de Sitter space. background 1.00 0.06 0.04 asserted 0.99
s1 Matter fields in anti-de Sitter space can be in stable equilibrium even if the potential energy is unbounded from below, violating the weak energy condition. background 0.87 0.13 0.07 asserted 0.86
s2 Hence there is no fundamental reason that black hole's horizons should have spherical topology. interpretation 0.79 0.16 0.47 asserted 0.94
s3 In anti-de Sitter space the Einstein's equations admit black hole solutions where the horizon can be a Riemann surface with genus $g$. result 0.59 0.48 0.47 asserted 0.98
s4 The case $g=0$ is the asymptotically anti-de Sitter black hole first studied by Hawking-Page, which has spherical topology. background 0.98 0.06 0.06 asserted 1.00
s5 The genus one black hole has a new free parameter entering the metric, the conformal class to which the torus belongs. result 0.88 0.63 0.06 asserted 1.00
s6 The genus $g>1$ black hole has no other free parameters apart from the mass and the charge. result 0.93 0.66 0.10 asserted 1.00
s7 All such black holes exhibits a natural temperature which is identified as the period of the Euclidean continuation and there is a mass formula connecting the mass with the surface gravity and the horizon area of the black hole. result 0.95 0.68 0.17 asserted 1.00
s8 The Euclidean action and entropy are computed and used to argue that the mass spectrum of states is positive definite. result 0.84 0.85 0.21 asserted 0.98

What kind of paper the classifier reports this is: theoretical result 1.00 · evidence from proof or derivation 0.96.

What was examined, and what was not

sources read
  • arXiv listing abstract v3
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

References
How later papers used it

71 later papers cite it

Evidence: substantial. 71 of the citing papers share no author with it, and 6 of those carry a confident label from Pith's citation classifier.

Pith read 12 of the 110 citing sentences, choosing only those whose citation markers point at this paper alone, and wrote the paraphrases from them. The summary, the counts, the evidence level, the links and the quotes come from code; the summary counts the papers listed below. A later paper is listed under a label when Pith's citation classifier gives one of its sentences that label at probability 0.8 or more (0.95 for support), Pith's reading finds that the citing paper itself did it, and a second check confirms the paraphrase against the sentence. This section lists uses only. It does not list criticism or disagreement, so their absence here says nothing about how the paper has been received. Papers that share an author with this one are listed apart, under "By the same authors". A quote is the citing authors' own sentence, shown when their paper's licence is CC BY, CC BY-SA or CC0. JSON

Uses its method or tool 1 paper
Cites it as support 2 papers
  • Said that this supports the consideration of some of these extremal solutions as groundstates, citing this paper.

    Cosmic censorship in Lovelock theory (2013) · 0.98 · paraphrased: the licence does not allow quoting

  • Said that this supports the consideration of some of these extremal solutions as groundstates, citing this paper.

    Lovelock gravity, black holes and holography (2015) · 0.99 · paraphrased: the licence does not allow quoting

How the literature uses it

65 arXiv papers cite this in 99 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 · 51 sentences without a confident label

Builds on it 1 paper
  • Les trous noirs topologiques rencontr�s � la sous-section [ref] en dimension $D=4$ [ref] se g�n�ralisent facilement en dimension $D ≥4$ [ref] .

    Black hole solutions of modified gravity theories · La solution de Tangherlini et ses versions topologiques · 0.87

Uses its data or values 1 paper
  • The Hawking temperature of the MTBH is equal to [ref] – [ref] [equation] and from the QNF ([ref]) of the massless Dirac field we find [equation] We see that the first expression in formulas ([ref]) saturates the inequality ([ref]) and that the second expression does not satisfy the previously mentioned inequality.

    Quasinormal frequencies of the Dirac field in the massless topological black hole · Hod's bound · 0.89

Compares with it 1 paper
Cites it as support 1 paper
  • This supports the consideration of some of these extremal solutions as groundstates [ref] .

    Cosmic censorship in Lovelock theory · The puzzle of multi horizon black holes · 0.98

Cites it as background 38 papers

Discussion

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