REVIEW 3 major objections 4 minor 1 cited by
Black-Hole Thermodynamics from Gauge Freedom in Extended Iyer-Wald Formalism
T0 review · 3 major / 4 minor · reviewed 2026-08-06 · deepseek-v4-flash
Pith's one-line read The paper claims that exact isohomogeneous transformations, which rescale a thermodynamic potential while preserving its variables and first law, are realized in the extended Iyer-Wald formalism by a Killing-field rescaling plus a gauge…
desk verdict A real but niche step connecting EITs to Iyer-Wald gauge choices; the KadS application rests on an unproved existence claim in Appendix C. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The central object is the exact isohomogeneous transformation, defined by $M_1 = gM_0$, $T_1 = gT_0 + M_0\,\partial g/\partial S$, and the analogous replacements for the other conjugate variables, with $g$ homogeneous of degree zero and the shift function equal to $M_0$; because it pulls the contact form back by $g$, it is a contactomorphism. The geometric machinery is the extended Iyer-Wald formalism with a potential volume $V = \int \star\omega$ built from the contraction of the volume form with the horizon Killing field; the gauge freedom is the allowed addition of a closed form $\star\lambda$. An EIT is implemented by rescaling the horizon Killing field and shifting $\omega_0$ by $\lambda$, with the three parameters fixed by the integrability conditions, and it converts a non-integrable $\delta M$ into an exact differential $dM_1$.
What would settle it
One could look for a stationary black-hole spacetime with a cosmological constant for which $\nabla_\mu \omega^{\mu\nu} = \xi^\nu$ has no smooth global solution; for such a spacetime the potential volume (35) and the gauge form (56) cannot be built and the claimed integrable first law is not constructible.
Extended reading notes
Core claim
The paper establishes that exact isohomogeneous transformations admit a geometric realization inside the extended Iyer-Wald formalism. The realization combines a Killing-field transformation $K_0 \to aK_0$ (Eq. 41) with a gauge transformation of the potential form $\star\omega_0 \to a\star\omega_0 + \star\lambda$ (Eq. 51), where the parameters $a$ and $b$ and the closed form $\star\lambda$ are fixed by Eqs. (49), (50), and (53). This guarantees that the operator $\delta$ can be replaced by $d$ in the first-law expression, so $M_1 = gM_0$ is integrable and is a true thermodynamic potential. For Kerr-anti de Sitter, the gauge choice $g = 1/\sqrt{\Xi}$ recovers the conventional first law $dM_U = T_U\,dS + \Omega_U\,dJ + V_U\,dP$, and the difference between thermodynamic and geometric volumes is identified as a gauge term.
Load-bearing premise
The construction stands on the existence of a global potential for the volume form (and, in the Kerr-anti de Sitter example, a closed but non-exact form whose existence is asserted rather than proved); without such objects the gauge transformation is not defined.
Editorial extensions
If this is right
- Every thermodynamic description obtained from an integrable first law by an exact isohomogeneous transformation acquires a geometric Iyer-Wald realization, replacing the earlier ad hoc extraction of an exact differential from a non-integrable variation.
- The conventional ‘usual thermodynamic theory’ of Kerr-anti de Sitter, with first law $dM_U = T_U\,dS + \Omega_U\,dJ + V_U\,dP$, is recovered as the special gauge choice $g = 1/\sqrt{\Xi}$.
- The known discrepancy between the thermodynamic and geometric volumes of Kerr-anti de Sitter is re-interpreted as a gauge term rather than a fixed property of the spacetime.
- Because exact isohomogeneous transformations are contactomorphisms and Legendre transformations form a subset, Legendre-based potentials also fit inside the same geometric framework.
- The family with $(g,h) = (\Xi^n, M_A)$ generates infinitely many equivalent, integrable first laws for Kerr-anti de Sitter.
Reading between the lines
- If this construction is right, the gauge-fixing mechanism should extend to other diffeomorphism-invariant theories with free parameters wherever a global potential for the volume form exists; the case-by-case condition in Eq. (23) is the main restriction to check.
- If this construction is right, the gauge dependence of mass and volume may carry physical information about observers, so an operational rule for choosing the gauge could give the thermodynamic volume a concrete meaning.
- If this construction is right, the use of a closed non-exact form in Appendix C points to a topological condition for matching potential and vector volumes, making spacetimes with different horizon topologies a natural test of how general the Kerr-anti de Sitter result is.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper develops a gauge-theoretic extension of the Iyer–Wald formalism in which the black-hole mass and thermodynamic volume are gauge dependent, and it shows that exact isohomogeneous transformations (EITs), introduced by the authors in previous work, can be realized geometrically by a simultaneous rescaling of the horizon Killing vector and a gauge shift of the Killing potential. The central construction is in Section IV: starting from an integrable first law dM0 = (κ0/2π)d(A/4) + Ω0dJ + V0dP, the authors define a transformed Killing vector K1 = aK0 and a transformed potential ⋆ω1 = a⋆ω0 + ⋆λ, with a, b, and λ fixed by Eqs. (49), (50), and (53), so that the transformed Iyer–Wald variation satisfies the EIT first law and δ can be replaced by d. In Section V, the gauge function g = 1/√Ξ is used to derive the conventional Kerr-AdS first law from the authors' 'alternative thermodynamic theory' (ATT), with explicit formulas for the UTT quantities in Eq. (71). The paper also provides a contact-geometric interpretation of EITs in Section II, a treatment of nonexact transformations in Appendix B, and an attempt to match vector and potential volumes in Appendix C.
Significance. If the gaps identified below are closed, the framework would provide a systematic and unifying explanation of the multiple first-law formulations of Kerr-AdS thermodynamics, showing that the difference between thermodynamic and geometric volumes is a gauge artifact. The explicit matching of the EIT parameters a, b, λ with the extended Iyer–Wald charges is a constructive step that goes beyond earlier ad hoc treatments, and the contact-geometric interpretation of EITs is a useful contribution. The paper does not provide machine-checked proofs or code, but the algebraic framework is transparent enough for the key identities to be checked by an independent computation. The main results are, however, conditional on resolving two technical issues: the treatment of the variation of a and b in Section IV, and the global existence of the Killing potential in Appendix C.
major comments (3)
- [Section IV, Eqs. (41)–(47)] The derivation of Eq. (47) from Eqs. (45)–(46) treats a (and implicitly b) as constants under the variation, while Eqs. (49)–(50) later define a and b as functions of the thermodynamic state through g(S,J,P). If K1 is fixed with respect to ¯δ as stated and the gauge δξ0μ=0=δφμ is used, then δξ1 = δa ξ0 + δb φ = 0 forces δa = δb = 0, which is incompatible with the state dependence of Eqs. (49)–(50). If, instead, a and b are allowed to vary, Eqs. (45)–(46) omit terms proportional to δa and δb. Since Eq. (47) is the step that licenses the replacement of δ by d, this inconsistency must be resolved before the central integrability claim is established.
- [Appendix C and Section V, Eqs. (63)–(69)] The assertion that the ATT has a globally well-defined Killing potential ωA with VA = ∫_{σH} ωA is not proved. Equation (C2) uses the symbol θ for both a 2-form and a scalar integral, and Eq. (C3) assumes both the existence of a closed non-exact θ on KadS and the finiteness of lim_{σ→0} ∫σ ⋆ω, which are precisely the points at issue. Because the gauge construction in Eq. (69) and the ATT first law in Eq. (64) require ωA to be smooth on the exterior region, the local Poincaré lemma used in Eq. (32) is insufficient. This is a load-bearing gap for the Kerr-AdS application.
- [Section V, after Eq. (67)] The claim that the UTT first law is obtained 'without the need of any prior knowledge of the resulting theory' is overstated. The gauge function g = 1/√Ξ is chosen specifically to reproduce the known UTT first law, so the derivation is a consistency check that confirms the formalism can reproduce a selected gauge, not an independent derivation of that gauge. The paper should be reworded to make this distinction explicit.
minor comments (4)
- [Section IIB, Eq. (8)] The Reeb vector for the contact form η in Eq. (7) is not generally ξ = -∂/∂S unless the intensive variables are independent of S; as stated, homogeneity of degree zero does not imply independence from S. Either provide a proof under the stated assumptions or qualify the statement.
- [Notation, Sections IV–V] The transformation parameter a in Eqs. (41)–(53) and the rotation parameter a in Eqs. (57)–(71) share the same symbol, which is confusing in Section V where both appear. Rename one of them, for example by using α for the transformation parameter.
- [Appendix C, Eq. (C2)] Using the same symbol θ for a 2-form and for its integral makes the definition of θ′ ambiguous; distinct notation for the form and its period should be introduced.
- [Section V, final paragraph and footnote 6] There are typos: 'ETIs' should be 'EITs', and 'Is is also interesting' should be 'It is also interesting'.
Circularity Check
The KadS 'recovery' of UTT is selected by choosing g=1/√Ξ, so the advertised emergence reduces by construction; the central geometric construction itself is self-contained, but the application relies on a load-bearing unproved/self-cited existence assumption.
-
fitted input called prediction
[Section V, Eq. (67) and discussion after Eq. (71), pages 10-11]
"Among these infinite possibilities, a more usual (and fairly explored) thermodynamic description of KadS black holes [25] can be obtained using the following exact isohomogeneous transformation from the ATT: (g, h) = (1/√Ξ, M_A), Ξ(J, S, P) = (1 + 8π/3 J^2P/M_A^2)^{-1} . ... It demonstrates that our extended Iyer–Wald formalism reproduces the usual KadS thermodynamic theory for the Killing vector K_U of Equation (68), without the need of any prior knowledge of the resulting theory."
The gauge function g in Eq. (67) is not derived from first principles; it is explicitly chosen to be the inverse of the transformation that produced the ATT from Hawking's description, and Ξ is engineered so that the output is the known UTT of [25]. Eq. (70) is therefore the target encoded in the input g, not an independent prediction. The paper itself concedes in Section IV that 'the best that can be done is to fix this gauge so that it reproduces a desired value of M,' and the later claim that UTT is reproduced 'without the need of any prior knowledge of the resulting theory' directly contradicts that admission. This is a fitted input called a demonstration.
-
self citation load bearing
[Section V, Eq. (66) and Appendix C, Eqs. (C1)-(C3), pages 10 and 13]
"In Appendix C a proof that this ω_A exists is presented. ... Then, because there exists a θ in KadS, V_v = lim_{σ→0} ∫_{σ_H}^{σ} ı_v(⋆1) = lim_{σ→0} ∫_σ (⋆ω + θ′) + ∫_{σ_H} (⋆ω + θ′) = ∫_{σ_H} (⋆ω + θ′), which completes the proof since θ′ is closed."
The KadS application requires a global Killing potential ω_A so that V_A in Eq. (66) is a genuine potential volume and the ATT first law (64) is a proper starting point. Appendix C attempts to prove the needed gauge exists, but its construction defines θ′ using a closed non-exact θ whose existence is asserted by the phrase 'because there exists a θ in KadS' rather than demonstrated by an explicit θ, periods, or regularity argument. The only cited basis for the vector-volume statement is the authors' own [8]. Thus the load-bearing premise for the KadS derivation is supported by an asserted existence and a self-citation, not by an independent proof.
full rationale
The central formalism of Sections II-IV is not circular: EITs are defined independently in Eq. (2), their contact-geometric character is shown in Section II.B, and the Killing-field parameters a,b and gauge form λ in Eqs. (49)-(53) are solved, not assumed, to realize the EIT within the extended Iyer-Wald framework. That part is a self-contained construction anchored to Hawking's external formulas. The circularity is in the advertised application: the UTT first law of Eq. (70) is recovered because Eq. (67) selects g=1/√Ξ, which is precisely the transformation that maps the ATT to UTT; the target is therefore an input. The paper's own admission in Section IV that the gauge is fixed to reproduce a desired value of M makes this explicit, and the assertion that this happens 'without the need of any prior knowledge of the resulting theory' overstates the case. Additionally, the existence of the global Killing potential ω_A and closed non-exact θ needed for the ATT starting point is asserted in Appendix C and attributed to the authors' prior work [8], rather than proved; this is a load-bearing proof gap/self-citation. Because the formalism has substantial independent content and the circularity is confined to the demonstrative KadS application, the score is 6 rather than higher.
Assumptions & free parameters
free parameters (2)
- EIT scale function g(S,J,P) =
g = 1/sqrt(Ξ) for the UTT application, with Ξ given implicitly by Eq.
- ATT renormalization factor sqrt(Ξ) =
MA = MH/sqrt(Ξ), TA = TH/sqrt(Ξ), VA = VH/sqrt(Ξ) in Eqs. (63)-(65)
assumptions (4)
- standard math Poincaré lemma: every closed form is locally exact, applied to i_ξ(*1) and to λ
- ad hoc to paper Global existence of the Killing potential ω and of a closed non-exact form θ in KadS
- domain assumption The ATT is a legitimate thermodynamic representation and a valid starting point for EITs
- domain assumption Vacuum Einstein equations imply the conservation identity ∇_μ(∇^μξ^ν + Λω^μν)=0 for Killing vectors with a potential
invented entities (1)
-
Potential-volume gauge form λ
Cite this review
Pith. "Pith review of Black-Hole Thermodynamics from Gauge Freedom in Extended Iyer-Wald Formalism." pith.science (2026). https://pith.science/paper/66MRLVH2
@misc{pith2026250703751,
author = {Pith},
title = {Pith review of: Black-Hole Thermodynamics from Gauge Freedom in Extended Iyer-Wald Formalism},
year = {2026},
howpublished = {\url{https://pith.science/paper/66MRLVH2}},
note = {Machine review of arXiv:2507.03751}
}
read the original abstract
Thermodynamic systems admit multiple equivalent descriptions related by transformations that preserve their fundamental structure. This work focuses on exact isohomogeneous transformations (EITs), a class of mappings that keep fixed the set of independent variables of the thermodynamic potential, while preserving both the original homogeneity and the validity of a first law. Our investigation explores EITs within the extended Iyer--Wald formalism for theories containing free parameters (e.g., the cosmological constant). EITs provide a unifying framework for reconciling the diverse formulations of Kerr-anti de Sitter (KadS) thermodynamics found in the literature. While the Iyer--Wald formalism is a powerful tool for deriving first laws for black holes, it typically yields a non-integrable mass variation that prevents its identification as a proper thermodynamic potential. To address this issue, we investigate an extended Iyer--Wald formalism where mass and thermodynamic volume become gauge dependent. Within this framework, we identify the gauge choices and Killing vector normalizations that are compatible with EITs, ensuring consistent first laws. As a key application, we demonstrate how conventional KadS thermodynamics emerges as a special case of our generalized approach.
Forward citations
Cited by 1 Pith paper
-
The Role of the Volume in Black Hole Thermodynamics
Conserved charges built from a Kerr-Schild background show the first law requires the Killing vector and AdS background to be held fixed, explaining why the rotating-frame energy F fails while E works, and why the geo...
Reference graph
Works this paper leans on
-
[1]
Contact Symmetries and Hamiltonian Thermodynamics.Ann
Bravetti, A.; Lopez-Monsalvo, C.S.; Nettel, F. Contact Symmetries and Hamiltonian Thermodynamics.Ann. Phys. 2015, 361, 377–400
work page 2015
-
[2]
Some Properties of Noether Charge and a Proposal for Dynamical Black Hole Entropy.Phys
Iyer, V.; Wald, R. Some Properties of Noether Charge and a Proposal for Dynamical Black Hole Entropy.Phys. Rev. D 1994, 50, 846–864
work page 1994
-
[3]
Black hole entropy is the Noether charge.Phys
Wald, R. Black hole entropy is the Noether charge.Phys. Rev. D 1993, 48, R3427
work page 1993
-
[4]
Hajian, K.; Sheikh-Jabbari, M.M. Solution phase space and conserved charges: A general formulation for charges associated with exact symmetries.Phys. Rev. D 2016 93, 044074. arXiv:1512.05584
arXiv 2016
-
[5]
Extended black hole thermodynamics from extended Iyer–Wald formalism.Phys
Xiao, Y.; Tian, Y.; Liu, Y.X. Extended black hole thermodynamics from extended Iyer–Wald formalism.Phys. Rev. Lett. 2024, 132, 021401. arXiv:2308.12630
arXiv 2024
-
[6]
Enthalpy and the mechanics of adS black holes.Class
Kastor, D.; Ray, S.; Traschen, J. Enthalpy and the mechanics of adS black holes.Class. Quant. Grav. 2019, 26, 195011. arXiv:0904.2765
arXiv 2019
-
[7]
Black hole chemistry: thermodynamics with LambdaClass
Kubiznak, D.; Mann, R.B.; Teo, M. Black hole chemistry: thermodynamics with LambdaClass. Quantum Grav. 2017, 34, 063001. arXiv:1608.06147
arXiv 2017
-
[8]
Generating Kerr-anti-de Sitter thermodynamics.Phys
Campos, T.; Baldiotti, M.C.; Molina, C. Generating Kerr-anti-de Sitter thermodynamics.Phys. Rev. D 2024, 110, 024049. arXiv:2407.09610
arXiv 2024
Show all 25 references
-
[9]
General mass formulas for charged Kerr–adS black holes
Gao, Y.; Di, Z.; Gao, S. General mass formulas for charged Kerr–adS black holes. Phys. Scr. 2024, 99, 095022. arXiv:2304.10290
2024 arXiv
-
[10]
The First Law of Thermodynamics for Kerr-Anti-de Sitter Black Holes.Class
Gibbons, G.W.; Perry, M.J.; Pope, C.N. The First Law of Thermodynamics for Kerr-Anti-de Sitter Black Holes.Class. Quant. Grav. 2005, 22, 1503. arXiv:hep-th/0408217
2005 arXiv
-
[11]
Rotation and the AdS/CFT correspondence.Phys
Hawking, S.W.; Hunter, C.J.; Taylor-Robinson, M.M. Rotation and the AdS/CFT correspondence.Phys. Rev. D 1999, 59, 064005. arXiv:hep-th/9811056
1999 arXiv
-
[12]
Baldiotti, M.C.; Fresneda, R.; Molina. C. A Hamiltonian approach to Thermodynamics.Ann. Phys. 2016, 373, 245–256. arXiv:1604.03117
2016 arXiv
-
[13]
Contact geometry and thermodynamics.Int
Bravetti, A. Contact geometry and thermodynamics.Int. J. Geom. Meth. Mod. Phys. 2018, 16, 1940003
2018
-
[14]
A Hamiltonian approach for the Thermodynamics of AdS black holes.Ann
Baldiotti, M.C.; Fresneda, R.; Molina, C. A Hamiltonian approach for the Thermodynamics of AdS black holes.Ann. Phys. 2017, 382, 22–35. arXiv:1701.01119
2017 arXiv
-
[15]
Extended quasilocal Thermodynamics of Schwarzchild-anti de Sitter black holes.Ann
Fontana, W.B.; Baldiotti, M.C.; Fresneda, R.; Molina, C. Extended quasilocal Thermodynamics of Schwarzchild-anti de Sitter black holes.Ann. Phys. 2019, 411, 167954. arXiv:1806.05699
2019 arXiv
-
[16]
Action integrals and partition functions in quantum gravity.Phys
Gibbons, G.W.; Hawking, S.W. Action integrals and partition functions in quantum gravity.Phys. Rev. D 1977, 15, 2752
1977
-
[17]
Metric geometry of equilibrium thermodynamics.J
Weinhold, F. Metric geometry of equilibrium thermodynamics.J. Chem. Phys. 1975, 63, 2479
1975
-
[18]
Noether charge, black hole volume, and complexity.J
Couch, J.; Fischler, W.; Nguyen, P.H. Noether charge, black hole volume, and complexity.J. High Energy Phys. 2017, 2017, 119. arXiv:1610.02038
2017 arXiv
-
[19]
The Vector Volume and Black Hole.Phys
Ballik, W.; Lake, K. The Vector Volume and Black Hole.Phys. Rev. D 2013, 88, 104038. arXiv:1310.1935
2013 arXiv
-
[20]
The four laws of black hole mechanics.Commun
Bardeen, J.M.; Carter, B.; Hawking, S.W. The four laws of black hole mechanics.Commun. Math. Phys. 1973, 31, 161
1973
-
[21]
Pressure and volume in the first law of black hole thermodynamics.Class
Dolan, B.P. Pressure and volume in the first law of black hole thermodynamics.Class. Quant. Grav . 2011, 28, 235017. arXiv:1106.6260
2011 arXiv
-
[22]
Where is the PdV in the first law of black hole thermodynamics? InOpen Questions in Cosmology , 1st ed.; Olmo, G.J., Ed.; IntechOpen: Rijeka, Croatia, 2012; pp
Dolan, B.P. Where is the PdV in the first law of black hole thermodynamics? InOpen Questions in Cosmology , 1st ed.; Olmo, G.J., Ed.; IntechOpen: Rijeka, Croatia, 2012; pp. 291–315. arXiv:1209.1272
2012 arXiv
-
[23]
Cvetič, M.; Gibbons, G.W.; Kubizňák, D.; Pope, C.N.Blackholeenthalpyandanentropyinequalityforthethermodynamic volume. Phys. Rev. D 2011, 84, 024037. arXiv:1012.2888
2011 arXiv
-
[24]
First law for Kerr Taub-NUT AdS black holes.J
Rodríguez, N.H.; Rodriguez, M.J. First law for Kerr Taub-NUT AdS black holes.J. High Energy Phys. 2022, 2022, 44. arXiv:2112.00780
2022 arXiv
-
[25]
Thermodynamics of Kerr-Newmann-AdS black holes and conformal field theories
Caldarelli, M.; Cognola, G.; Klemm, D. Thermodynamics of Kerr-Newmann-AdS black holes and conformal field theories. Class. Quant. Grav. 2000, 17, 399. arXiv:hep-th/9908022
2000 arXiv
Reviewed August 6, 2026 · model on record in the stance chip above.
Discussion (0). Sign in to comment.