Recognition: unknown
g_{tt}g_{rr} =-1 black hole thermodynamics in extended quasi-topological gravity
Pith reviewed 2026-05-08 02:19 UTC · model grok-4.3
The pith
For black holes with g_tt g_rr = -1 the generating function of f(r) supplies the thermodynamic mass in a generalized first law using Wald entropy.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
Static black holes with g_tt g_rr = -1 are solutions of an integrable 2D effective dilaton theory and therefore vacuum solutions of d-dimensional extended quasi-topological gravity. The generating function that fixes f(r) = -g_tt in the integrated equation of motion therefore supplies the thermodynamic mass appearing in the generalized first law, with entropy given by the Wald prescription. The framework applies uniformly to spherical, toroidal and hyperbolic horizons and to both singular and regular solutions with flat or anti-de Sitter asymptotics.
What carries the argument
The generating function determining f(r) = -g_tt in the integrated equation of motion, which directly supplies the thermodynamic mass.
If this is right
- The thermodynamic mass is read off directly from the generating function without separate integration constants or asymptotic matching.
- Entropy follows automatically from the Wald formula for the underlying higher-derivative theory.
- The same first-law relation holds for spherical, toroidal and hyperbolic horizons alike.
- Both singular and regular black holes with flat or anti-de Sitter asymptotics are covered by the identical construction.
Where Pith is reading between the lines
- The reduction to an integrable 2D dilaton model may simplify thermodynamic calculations in other higher-curvature theories that admit similar static metrics.
- The approach suggests that many features of d-dimensional black-hole thermodynamics are already encoded in the 2D dilaton description for this restricted class of metrics.
- Similar generating-function techniques could be tested on time-dependent or non-static solutions that still obey g_tt g_rr = -1 in a suitable gauge.
Load-bearing premise
Any black hole satisfying g_tt g_rr = -1 can be treated as a solution of an integrable 2-dimensional effective dilaton theory and thereby as a vacuum solution of extended quasi-topological gravity.
What would settle it
An explicit black-hole solution with g_tt g_rr = -1 for which the value of the generating function fails to equal the mass required by the first law when entropy is computed via the Wald formula.
read the original abstract
We present a unified framework for the discussion of black hole thermodynamics of $d$-dimensional static black holes with spherical, toroidal or compact hyperbolic horizon topology satisfying $g_{tt}g_{rr}=-1$ in Schwarzschild gauge. To that end, we consider any such black hole as a solution to an integrable $2$-dimensional effective dilaton theory and thereby as a vacuum solution to an extended notion of $d$-dimensional quasi-topological gravity. We show that the generating function determining $f(r) = -g_{tt} $ in the integrated equation of motion provides the thermodynamic mass in a generalised first law with entropy computed as the Wald entropy. The framework presented here can be applied to singular and regular black holes with flat or anti-de Sitter asymptotics.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper presents a unified framework for black hole thermodynamics of d-dimensional static black holes (spherical, toroidal or hyperbolic horizons) obeying g_tt g_rr = -1 in Schwarzschild gauge. Any such metric is treated as a solution of an integrable 2D effective dilaton theory obtained by spherical reduction, which is asserted to be a vacuum solution of some extended d-dimensional quasi-topological gravity. The generating function that determines f(r) = -g_tt after integrating the equation of motion is identified as the thermodynamic mass conjugate to the Wald entropy in a generalized first law. The construction is claimed to apply uniformly to singular and regular solutions with flat or AdS asymptotics.
Significance. If the mapping from arbitrary f(r) to an extended quasi-topological Lagrangian is rigorously established, the result supplies a general, generating-function-based route to the first law that bypasses the need to fix the higher-dimensional action in advance and automatically incorporates the Wald entropy. This would unify thermodynamic calculations across a wide class of higher-curvature theories while remaining parameter-free once the 2D integrability is granted.
major comments (1)
- [framework construction (around the effective 2D theory and its lift)] The central identification of the generating function with thermodynamic mass rests on the claim that every metric with g_tt g_rr = -1 is a vacuum solution of some extended quasi-topological gravity. The manuscript must supply an explicit construction (or existence proof) of the d-dimensional Lagrangian whose spherical reduction reproduces an arbitrary integrable 2D dilaton model with the given f(r). Without this step, the 'thereby' step in the abstract remains an assumption rather than a derivation, and the thermodynamic interpretation does not follow for arbitrary f(r).
Simulated Author's Rebuttal
We thank the referee for their detailed review and for identifying the key point requiring clarification in the framework construction. We address the major comment below and will revise the manuscript accordingly to strengthen the derivation.
read point-by-point responses
-
Referee: The central identification of the generating function with thermodynamic mass rests on the claim that every metric with g_tt g_rr = -1 is a vacuum solution of some extended quasi-topological gravity. The manuscript must supply an explicit construction (or existence proof) of the d-dimensional Lagrangian whose spherical reduction reproduces an arbitrary integrable 2D dilaton model with the given f(r). Without this step, the 'thereby' step in the abstract remains an assumption rather than a derivation, and the thermodynamic interpretation does not follow for arbitrary f(r).
Authors: We agree that the manuscript would benefit from an explicit construction or existence proof to make the lift from the 2D effective dilaton theory to the d-dimensional extended quasi-topological gravity fully rigorous rather than asserted. In the revised version, we will add a dedicated subsection that constructs the d-dimensional Lagrangian explicitly. For any given integrable 2D dilaton model with arbitrary f(r) satisfying the g_tt g_rr = -1 condition, the spherical reduction of the extended quasi-topological action (built from the standard Lovelock terms plus the quasi-topological invariants that reduce to total derivatives or zero in spherical symmetry) can be matched term-by-term to the 2D action by solving for the coefficients of the higher-curvature polynomials. Because the quasi-topological terms provide sufficient freedom in their curvature invariants while preserving the integrability of the 2D equations, an existence proof follows from the invertibility of this coefficient-matching procedure for any smooth f(r) with the required asymptotic behavior. This will turn the 'thereby' statement into a derived result and confirm that the generating function is indeed the thermodynamic mass conjugate to the Wald entropy for arbitrary such solutions. revision: yes
Circularity Check
No significant circularity; framework assumption is explicit and derivation proceeds independently within it.
full rationale
The paper explicitly adopts the assumption that any g_tt g_rr=-1 black hole can be viewed as an integrable 2D dilaton solution and hence a vacuum solution in an extended quasi-topological gravity. Within this setup the integration of the effective equations yields a generating function that is then shown to enter the first law as mass when paired with Wald entropy. This identification follows from the structure of the 2D theory and the standard Wald formula rather than from re-labeling fitted parameters or self-referential definitions. No load-bearing self-citations, ansatzes smuggled via prior work, or uniqueness theorems imported from the same authors appear in the abstract or described chain. The central result is therefore self-contained once the initial mapping is granted.
Axiom & Free-Parameter Ledger
axioms (2)
- domain assumption Black holes with g_tt g_rr=-1 are solutions to an integrable 2D effective dilaton theory
- domain assumption These are vacuum solutions to extended quasi-topological gravity
Reference graph
Works this paper leans on
-
[1]
J. D. Bekenstein,Black holes and entropy,Phys. Rev. D7(1973) 2333–2346
1973
-
[2]
S. W. Hawking,Particle Creation by Black Holes, Commun. Math. Phys.43(1975) 199–220. [Erratum: Commun.Math.Phys. 46, 206 (1976)]
1975
-
[3]
R. M. Wald,Black hole entropy is the Noether charge, Phys. Rev. D48(1993), no. 8 R3427–R3431, [gr-qc/9307038]
work page Pith review arXiv 1993
-
[4]
Some Properties of Noether Charge and a Proposal for Dynamical Black Hole Entropy
V. Iyer and R. M. Wald,Some properties of Noether charge and a proposal for dynamical black hole entropy, Phys. Rev. D50(1994) 846–864, [gr-qc/9403028]
work page Pith review arXiv 1994
-
[5]
Renormalization group improved black hole spacetimes
A. Bonanno and M. Reuter,Renormalization group improved black hole space-times,Phys. Rev. D62 (2000) 043008, [hep-th/0002196]
work page Pith review arXiv 2000
-
[6]
Spacetime Structure of an Evaporating Black Hole in Quantum Gravity
A. Bonanno and M. Reuter,Spacetime structure of an evaporating black hole in quantum gravity,Phys. Rev. D73(2006) 083005, [hep-th/0602159]
work page Pith review arXiv 2006
-
[7]
Black holes and asymptotically safe gravity
K. Falls, D. F. Litim, and A. Raghuraman,Black Holes and Asymptotically Safe Gravity,Int. J. Mod. Phys. A27(2012) 1250019, [arXiv:1002.0260]
work page Pith review arXiv 2012
-
[8]
Structural aspects of asymptotically safe black holes
B. Koch and F. Saueressig,Structural aspects of asymptotically safe black holes,Class. Quant. Grav.31 (2014) 015006, [arXiv:1306.1546]
work page Pith review arXiv 2014
-
[9]
J. M. Pawlowski and D. Stock,Quantum-improved Schwarzschild-(A)dS and Kerr-(A)dS spacetimes, Phys. Rev. D98(2018), no. 10 106008, [arXiv:1807.10512]
work page Pith review arXiv 2018
-
[10]
A. Adeifeoba, A. Eichhorn, and A. B. Platania, Towards conditions for black-hole singularity-resolution in asymptotically safe quantum gravity,Class. Quant. Grav.35(2018), no. 22 225007, [arXiv:1808.03472]
-
[11]
Platania,Dynamical renormalization of black-hole spacetimes,Eur
A. Platania,Dynamical renormalization of black-hole spacetimes,Eur. Phys. J. C79(2019), no. 6 470, [arXiv:1903.10411]
-
[12]
A. Eichhorn and A. Held,Black holes in asymptotically safe gravity and beyond,arXiv:2212.09495
-
[13]
Platania,Black Holes in Asymptotically Safe Gravity
A. Platania,Black Holes in Asymptotically Safe Gravity. 2023.arXiv:2302.04272
-
[14]
F. Fragomeno, D. M. Gingrich, S. Hergott, S. Rastgoo, and E. Vienneau,A generalized uncertainty-inspired quantum black hole,Phys. Rev. D111(2025), no. 2 024048, [arXiv:2406.03909]
- [15]
-
[16]
A. Bonanno, M. Cadoni, M. Pitzalis, and A. P. Sanna, Effective quantum spacetimes from functional renormalization group,Phys. Rev. D111(2025), no. 6 064031, [arXiv:2410.16866]
-
[17]
Bardeen,Non-singular general-relativistic gravitational collapse,Abstracts of GR5 — the 5th international conference on gravitation and the theory of relativity, eds
J. Bardeen,Non-singular general-relativistic gravitational collapse,Abstracts of GR5 — the 5th international conference on gravitation and the theory of relativity, eds. V. A. Fock et al. (Tbilisi University Press, Tbilisi, Georgia, former USSR)(1968) 174–175
1968
-
[18]
Dymnikova,Vacuum nonsingular black hole,Gen
I. Dymnikova,Vacuum nonsingular black hole,Gen. Rel. Grav.24(1992) 235–242
1992
-
[19]
S. A. Hayward,Formation and evaporation of regular black holes,Phys. Rev. Lett.96(2006) 031103, [gr-qc/0506126]
work page Pith review arXiv 2006
-
[20]
Regular Black Hole in General Relativity Coupled to Nonlinear Electrodynamics
E. Ayon-Beato and A. Garcia,Regular black hole in general relativity coupled to nonlinear electrodynamics, Phys. Rev. Lett.80(1998) 5056–5059, [gr-qc/9911046]
work page Pith review arXiv 1998
-
[21]
E. Ayon-Beato and A. Garcia,Nonsingular charged black hole solution for nonlinear source,Gen. Rel. Grav.31(1999) 629–633, [gr-qc/9911084]
-
[22]
E. Ayon-Beato and A. Garcia,New regular black hole solution from nonlinear electrodynamics,Phys. Lett. B 464(1999) 25, [hep-th/9911174]
-
[23]
The Bardeen Model as a Nonlinear Magnetic Monopole
E. Ayon-Beato and A. Garcia,The Bardeen model as a nonlinear magnetic monopole,Phys. Lett. B493 (2000) 149–152, [gr-qc/0009077]
work page Pith review arXiv 2000
-
[24]
K. A. Bronnikov,Regular magnetic black holes and monopoles from nonlinear electrodynamics,Phys. Rev. D63(2001) 044005, [gr-qc/0006014]
work page Pith review arXiv 2001
-
[25]
I. Dymnikova,Regular electrically charged structures in nonlinear electrodynamics coupled to general relativity, Class. Quant. Grav.21(2004) 4417–4429, [gr-qc/0407072]
- [26]
-
[27]
Regular black holes with a nonlinear electrodynamics source
L. Balart and E. C. Vagenas,Regular black holes with a nonlinear electrodynamics source,Phys. Rev. D90 (2014), no. 12 124045, [arXiv:1408.0306]
work page Pith review arXiv 2014
-
[28]
Construction of Regular Black Holes in General Relativity
Z.-Y. Fan and X. Wang,Construction of Regular Black Holes in General Relativity,Phys. Rev. D94(2016), no. 12 124027, [arXiv:1610.02636]
work page Pith review arXiv 2016
-
[29]
M. E. Rodrigues and M. V. de Sousa Silva,Bardeen Regular Black Hole With an Electric Source,JCAP06 (2018) 025, [arXiv:1802.05095]
work page Pith review arXiv 2018
-
[30]
A. A. Ara´ ujo Filho, E. L. B. Junior, J. T. S. S. Junior, F. S. N. Lobo, J. A. A. Ramos, M. E. Rodrigues, D. Rubiera-Garcia, L. F. D. da Silva, and H. A. Vieira, Regular Black Holes in General Relativity from Nonlinear Electrodynamics with de Sitter Cores, arXiv:2604.20066
work page internal anchor Pith review Pith/arXiv arXiv
-
[31]
Banks and M
T. Banks and M. O’Loughlin,Two-dimensional quantum gravity in Minkowski space,Nucl. Phys. B 362(1991) 649–664
1991
-
[32]
D. Louis-Martinez, J. Gegenberg, and G. Kunstatter, Exact Dirac quantization of all 2-D dilaton gravity 8 theories,Phys. Lett. B321(1994) 193–198, [gr-qc/9309018]
-
[33]
Dilaton Gravity in Two Dimensions
D. Grumiller, W. Kummer, and D. V. Vassilevich, Dilaton gravity in two-dimensions,Phys. Rept.369 (2002) 327–430, [hep-th/0204253]
work page Pith review arXiv 2002
-
[34]
All $2D$ generalised dilaton theories from $d\geq 4$ gravities
J. Borissova,All2Dgeneralised dilaton theories from d≥4gravities,arXiv:2603.06786
work page internal anchor Pith review Pith/arXiv arXiv
-
[35]
G. W. Horndeski,Second-order scalar-tensor field equations in a four-dimensional space,Int. J. Theor. Phys.10(1974) 363–384
1974
-
[36]
Generalized G-inflation: Inflation with the most general second-order field equations
T. Kobayashi, M. Yamaguchi, and J. Yokoyama, Generalized G-inflation: Inflation with the most general second-order field equations,Prog. Theor. Phys.126(2011) 511–529, [arXiv:1105.5723]
work page Pith review arXiv 2011
-
[37]
J. Borissova and R. Carballo-Rubio,Regular black holes from pure gravity in four dimensions, arXiv:2602.16773
-
[38]
R. S. Palais,The principle of symmetric criticality, Commun. Math. Phys.69(1979), no. 1 19–30
1979
- [39]
-
[40]
S. Deser and B. Tekin,Shortcuts to high symmetry solutions in gravitational theories,Class. Quant. Grav. 20(2003) 4877–4884, [gr-qc/0306114]
- [41]
-
[42]
G. Frausto, I. Kol´ aˇ r, T. M´ alek, and C. Torre, Symmetry reduction of gravitational Lagrangians,Phys. Rev. D111(2025), no. 6 064062, [arXiv:2410.11036]
-
[43]
Regular Vaidya solutions of effective gravitational theories
V. Boyanov and R. Carballo-Rubio,Regular Vaidya solutions of effective gravitational theories, arXiv:2506.14875
work page internal anchor Pith review Pith/arXiv arXiv
-
[44]
R. Carballo-Rubio,Master field equations for spherically symmetric gravitational fields beyond general relativity,Nature Commun.17(2026), no. 1 1399, [arXiv:2507.15920]
-
[45]
Lanczos,A Remarkable property of the Riemann-Christoffel tensor in four dimensions,Annals Math.39(1938) 842–850
C. Lanczos,A Remarkable property of the Riemann-Christoffel tensor in four dimensions,Annals Math.39(1938) 842–850
1938
-
[46]
Lovelock,Divergence-free tensorial concomitants, Aequat
D. Lovelock,Divergence-free tensorial concomitants, Aequat. Math.4(1970), no. 1 127–138
1970
-
[47]
Lovelock,The Einstein tensor and its generalizations,J
D. Lovelock,The Einstein tensor and its generalizations,J. Math. Phys.12(1971) 498–501
1971
-
[48]
J. Oliva and S. Ray,A new cubic theory of gravity in five dimensions: Black hole, Birkhoff’s theorem and C-function,Class. Quant. Grav.27(2010) 225002, [arXiv:1003.4773]
- [49]
- [50]
-
[51]
A. Cisterna, L. Guajardo, M. Hassaine, and J. Oliva, Quintic quasi-topological gravity,JHEP04(2017) 066, [arXiv:1702.04676]
-
[52]
P. Bueno, P. A. Cano, J. Moreno, and ´A. Murcia,All higher-curvature gravities as Generalized quasi-topological gravities,JHEP11(2019) 062, [arXiv:1906.00987]
- [53]
- [54]
-
[55]
J. Moreno and ´A. J. Murcia,Classification of generalized quasitopological gravities,Phys. Rev. D108 (2023), no. 4 044016, [arXiv:2304.08510]
- [56]
-
[57]
P. Bueno, P. A. Cano, and R. A. Hennigar,Regular black holes from pure gravity,Phys. Lett. B861(2025) 139260, [arXiv:2403.04827]
- [58]
- [59]
-
[60]
R. L. Arnowitt, S. Deser, and C. W. Misner, Dynamical Structure and Definition of Energy in General Relativity,Phys. Rev.116(1959) 1322–1330
1959
-
[61]
R. L. Arnowitt, S. Deser, and C. W. Misner,The Dynamics of general relativity,Gen. Rel. Grav.40 (2008) 1997–2027, [gr-qc/0405109]
work page Pith review arXiv 2008
- [62]
-
[63]
F. Di Filippo, I. Kol´ aˇ r, and D. Kubiznak, Inner-extremal regular black holes from pure gravity, Phys. Rev. D111(2025), no. 4 L041505, [arXiv:2404.07058]
- [64]
- [65]
- [66]
- [67]
- [68]
-
[69]
V. P. Frolov and A. Zelnikov,Regular Black Holes in Quasitopological Gravity: Null Shells and Mass Inflation,arXiv:2601.01861
work page internal anchor Pith review Pith/arXiv arXiv
- [70]
- [71]
-
[72]
Cosmic Inflation From Regular Black Holes
K. Sueto, R. Yoshimoto, and P. A. Cano,Cosmic Inflation From Regular Black Holes, arXiv:2604.04601
work page internal anchor Pith review Pith/arXiv arXiv
-
[73]
Charged Black Holes in Quasi-Topological Gravity Coupled to Born-Infeld Nonlinear Electrodynamics
J. Pinedo Soto and V. P. Frolov,Charged Black Holes in Quasi-Topological Gravity Coupled to Born-Infeld Nonlinear Electrodynamics,arXiv:2604.06632
work page internal anchor Pith review Pith/arXiv arXiv
- [74]
-
[75]
B. C. L¨ utf¨ uo˘ glu,Long-lived quasinormal modes, shadows and particle motion in four-dimensional quasi-topological gravity,arXiv:2603.10844
work page internal anchor Pith review Pith/arXiv arXiv
-
[76]
A. Dubinsky,Scattering of a scalar field in the four-dimensional quasi-topological gravity, arXiv:2603.17644
-
[77]
Z. Malik,Thermodynamic, Optical, and Orbital Signatures of Regular Asymptotically Flat Black Holes in Quasi-Topological Gravity,arXiv:2603.24212
-
[78]
From Ringdown to Lensing: Analytic Eikonal Modes of Quasi-Topological Regular Black Holes
A. Dubinsky,From Ringdown to Lensing: Analytic Eikonal Modes of Quasi-Topological Regular Black Holes,arXiv:2604.13613
work page internal anchor Pith review Pith/arXiv arXiv
-
[79]
Colleaux,Regular black hole and cosmological spacetimes in Non-Polynomial Gravity theories
A. Colleaux,Regular black hole and cosmological spacetimes in Non-Polynomial Gravity theories. PhD thesis, Trento U., 6, 2019
2019
-
[80]
J. Borissova and R. Carballo-Rubio,Effective geometrodynamics for renormalization-group improved black-hole spacetimes in spherical symmetry, arXiv:2601.17115
work page internal anchor Pith review arXiv
discussion (0)
Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.