REVIEW 3 major objections 4 minor 73 references
Exact charged and rotating toroidal black hole in the Einstein $SU(N)$-Skyrme model
T0 review · 3 major / 4 minor · reviewed 2026-08-11 · deepseek-v4-flash
Pith's one-line read An exact charged and rotating toroidal black hole is constructed in the Einstein-SU(N)-Skyrme-Maxwell system, valid for any flavor number N.
desk verdict A plausible local construction of a charged rotating toroidal Skyrme black hole, but the boosted matter field is not single-valued on the torus for generic ω, leaving the global interpretation in doubt. 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 construction is carried by two objects. The first is the maximal embedding of SU(2) into SU(N) in Euler angles, which packages the flavor number into the single constant $a_N = N(N^2-1)/6$ that controls every matter contribution in the metric and thermodynamic quantities. The second is the improper coordinate transformation (25), a Lorentz boost in the $(t,\phi)$ plane, which turns the static toroidal black hole into a locally static but globally stationary rotating metric and must be applied to the Skyrme field as well; the Maxwell potential is transformed in the same way.
What would settle it
Check the holonomy of the Skyrme field $U$ around the nontrivial cycle $\phi \to \phi + 2\pi$ at fixed $t, r, \theta$: if $U$ does not return to its starting value for generic $\omega$, the field is not single-valued and the claimed global toroidal black hole does not exist.
Extended reading notes
Core claim
The central discovery is that the stationary metric (26), with lapse function f(r) given by (46), together with the Skyrme field (27) and the Maxwell potential (53), is an exact solution of the complete Einstein-SU(N)-Skyrme-Maxwell equations. Rotation comes from applying the improper coordinate transformation (25) to the static seed solution, which boosts the t-phi plane and simultaneously rotates the pion field; charge is added through a minimal U(1) gauge field whose potential is also transformed. Because the electric charge and the Skyrme quartic term enter the lapse at the same power of 1/$r^{2}$, the two contributions can be absorbed into a single effective coupling. The authors then derive the Hawking temperature, free energy, mass, angular momentum, electric charge, and entropy from the regularized Euclidean action and verify the first law for the family.
Load-bearing premise
The solution assumes the boosted Skyrme field $F_3 = q(\phi - (\omega/\ell)t)/\sqrt{1-\omega^2}$ is single-valued on the torus, meaning it returns to itself when $\phi$ is identified modulo $2\pi$; the paper does not prove this, and without it the configuration is only a local solution.
Editorial extensions
If this is right
- The first law of thermodynamics holds for the charged, rotating, hairy family, so the computed mass, angular momentum, charge, entropy, temperature, angular velocity, and electric potential are mutually consistent.
- For $\lambda = Q = 0$, the hairy rotating black hole has lower Gibbs free energy than the vacuum rotating toroidal black hole at the same temperature and angular velocity, so the hairy solution globally dominates in the grand canonical ensemble.
- Because the flavor number $N$ enters only through $a_N$, all solutions and thermodynamic quantities scale in a simple, predictable way with $N$.
- In the limit $\omega \to 0$, the rotating charged solution reduces to the static charged hairy black hole, and in the limit $q \to 0$, the mass and angular momentum reproduce the known rotating toroidal black hole of Lemos.
- The electric charge and the Skyrme quartic term contribute to the lapse at the same order in $1/r^2$, so the two can be combined into an effective coupling for the thermodynamic analysis.
Reading between the lines
- If the global periodicity issue with the boosted Skyrme field is resolved, this family could serve as a holographic dual for rotating, charged, flavored boundary plasmas, a direction the paper's QGP motivation suggests but does not develop.
- The same improper-boost technique might generate exact rotating solutions in other matter models whose fields depend linearly on the boosted coordinate, such as sigma models with spiral or helical boundary conditions.
- The mass bound that follows from the paper's equations may admit a sharper extremal-limit estimate, and a dedicated study of the hairy extremal configuration could reveal whether a Penrose-like bound applies to this family.
- The stability analysis is restricted to $\lambda = Q = 0$; extending it to the full charged, quartic case could reveal phase transitions between hairy and vacuum branches.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript constructs a new exact family of four-dimensional asymptotically locally AdS black holes with toroidal horizon in the Einstein-SU(N)-Skyrme-Maxwell theory. The construction starts from the static toroidal Skyrme black hole of Ref. [36], adds rotation by applying the improper coordinate transformation (25), and adds electric charge through the U(1) gauge field (53). The metric is Eq. (26) with lapse (46), the matter field is Eq. (27), and the thermodynamics are computed in the grand canonical ensemble via a regularized Euclidean action. The paper further claims that the first law is satisfied and that, in the NLSM limit, the hairy rotating solution is globally preferred over the vacuum solution. The central claim is that Eqs. (26)-(27) and (53) constitute an exact global charged rotating toroidal black hole for arbitrary flavor number N.
Significance. If correct, this would be a valuable analytic example: exact charged and rotating hairy black holes in four dimensions are rare, and the explicit dependence on the flavor number N could be useful for holographic applications and for testing no-hair ideas outside spherical symmetry. The paper's strengths are the explicit forms of the metric, matter and gauge fields, the analytic thermodynamic expressions, and the explicit free-energy comparison in the grand canonical ensemble. However, the global validity of the matter field on the toroidal quotient is not established, and this issue is load-bearing for the central claim.
major comments (3)
- [§III.A, Eqs. (26)-(27); §V.A] The central global-validity claim is not established. For the metric (12) to describe a toroidal horizon, the coordinates θ and φ must be periodically identified, but the paper never states the periods and never checks that the pionic field U(x) ∈ SU(N) is single-valued under those identifications. After the boost, at fixed t, φ → φ + 2π sends F3 to F3 + 2πq/√(1−ω²), so U → U·exp(2πqT3/√(1−ω²)). For N=2, exp(2πqT3/√(1−ω²)) = diag(e^{iπq/√(1−ω²)}, e^{−iπq/√(1−ω²)}), which is the identity only when q/√(1−ω²) is an even integer; for q=1, ω=1/2 it is not. Furthermore, the seed Ansatz (13) has F2=qθ, and under the torus identification θ ∼ θ+π the monodromy is e^{qπT2}, which for N=2, q=1 equals iσ_y and is not central; hence even the left-invariant current L is not single-valued. Thus Eqs. (26)-(27), and their charged version in §V.A, define at best a local solution on the universal cover, not a global toroidal black hole.
- [§III.A; §V.A] The exactness claim is asserted rather than verified. Section III.A states that 'one can check' that the Einstein-Skyrme system is completely solved, and §IV.A states that it is a direct computation to check the Maxwell and Skyrme equations, but no components of the field equations are displayed. Because the construction uses a non-global coordinate transformation and the matter field is transformed nontrivially, the authors should provide the explicit verification of the full Einstein-Skyrme-Maxwell system, including the cross terms generated by the boost, before the solution can be accepted as exact.
- [§III.B, Eqs. (36)-(40); §V.A, Eqs. (57)-(60)] The thermodynamic potentials E, J, S, and Q̃ are stated after 'some computations' with no derivation, and the first law is asserted without displaying the independent checks. In particular, the regularized Euclidean action (34)/(56) must be finite after the counterterm prescription (19) on the rotating background; this is not demonstrated. The authors should provide the on-shell evaluation of the Euclidean action and the derivation of the first law, especially because the global validity of the matter field is in question.
minor comments (4)
- [Eq. (12)] The ranges 0 ≤ θ < π and 0 ≤ φ < 2π do not by themselves define a torus; the periodic identifications of θ and φ should be stated explicitly, since the toroidal topology is essential to the paper and to the periodicity issue raised above.
- [Eqs. (35), (56)] There is a typographical inconsistency: 'Kκα_N' appears in Eqs. (35) and (56) where the coefficient should be Kκa_N, matching Eq. (11) and the surrounding formulas.
- [Section II.B, after Eq. (11)] The text refers to 'the energy-momentum tensor in Eq. (6)', but Eq. (6) is the parametrization of U; the energy-momentum tensor appears after Eq. (5) and is not numbered. The cross-reference should be corrected.
- [Acknowledgments] The heading 'Acknowlegdments' is misspelled and should read 'Acknowledgments'.
Circularity Check
No significant circularity: the charged rotating black hole is an explicit improper-boost extension of a prior static seed, and the thermodynamic potentials are computed rather than fitted.
full rationale
The derivation chain starts from the static toroidal SU(N)-Skyrme solution of Ref. [36] (quoted in Eqs. (12)-(14)), applies the improper gauge transformation (25) to metric (12), matter field (13), and later the Maxwell potential (43), giving (26), (27), and (53) with f(r) in (46). None of these outputs is assumed in the input: the boost and U(1) coupling are external construction steps, and the solution is checked by substitution into the field equations. The thermodynamics are obtained from the Euclidean action (16)-(19), with counterterms citing both the present authors' Ref. [36] and the independent Ref. [67]; the free energies (35), (49), (56) and potentials (57)-(60) are closed-form expressions, and no parameter is fitted to the quantities later called predictions. The first-law statement is an algebraic consistency check on independently computed E, J, S, and Q rather than a manufactured identity. The only caveats are non-circular: Ref. [36] is shared with the present authors, so the seed is self-cited (though directly checkable), and the transformation (25) is admitted to be only locally a coordinate transformation, which raises a global single-valuedness question for (27) on the torus but is not a circularity. Overall, the central exact-solution claim has independent content despite reliance on a prior self-cited seed.
Assumptions & free parameters
free parameters (3)
- q (Skyrme winding / hair parameter) =
integer (unspecified)
- Q (electric charge parameter) =
real constant
- omega (rotation parameter) =
0 <= omega^2 < 1
assumptions (5)
- domain assumption Maximal embedding ansatz (6)-(9) for the Skyrme field U(x)
- domain assumption Seed static toroidal black hole (12)-(14) from Ref. [36]
- domain assumption Improper transformation (25) descends to the toroidal quotient and preserves the topology
- domain assumption Euclidean action with counterterms (16)-(19) yields the correct thermodynamic potentials
- domain assumption Grand canonical free energy comparison with the q=0 vacuum is the correct stability criterion
Cite this review
Pith. "Pith review of Exact charged and rotating toroidal black hole in the Einstein $SU(N)$-Skyrme model." pith.science (2026). https://pith.science/paper/P7VXWS2E
@misc{pith2026241212343,
author = {Pith},
title = {Pith review of: Exact charged and rotating toroidal black hole in the Einstein $SU(N)$-Skyrme model},
year = {2026},
howpublished = {\url{https://pith.science/paper/P7VXWS2E}},
note = {Machine review of arXiv:2412.12343}
}
abstract
In this paper, we construct an exact solution of the Einstein $SU(N)$-Skyrme model in $D=4$ space-time dimensions describing a charged and rotating black hole with toroidal horizon. Rotation is added by applying an improper coordinate transformation to the known static toroidal black hole with Skyrme hair, while the electric charge is supplemented by considering a $U(1)$ gauge field interacting with Einstein gravity. We perform the thermal analysis in the grand canonical ensemble, explicitly showing the role that the flavor number plays. Some discussions about stability are also considered.
Figures
Reference graph
Works this paper leans on
-
[36]
M. Astorino, F. Canfora, M. Lagos and A. Vera, Phys. Rev. D 97, no.12, 124032 (2018)
work page 2018
- [1]
-
[2]
J. D. Bekenstein, [arXiv:gr-qc/9605059 [gr-qc]]
- [3]
-
[4]
S. Droz, M. Heusler and N. Straumann, Phys. Lett. B 268, 371-376 (1991)
work page 1991
- [5]
-
[6]
M. S. Volkov and D. V. Galtsov, JETP Lett. 50, 346-350 (1989)
work page 1989
-
[7]
B. R. Greene, S. D. Mathur and C. M. O’Neill, Phys. Rev. D 47, 2242-2259 (1993)
work page 1993
Show all 73 references
-
[8]
Torii and K
T. Torii and K. i. Maeda, Phys. Rev. D 48, 1643-1651 (1993)
1993
-
[9]
Heusler, S
M. Heusler, S. Droz and N. Straumann, Phys. Lett. B 285, 21-26 (1992)
1992
-
[10]
T. H. R. Skyrme, Proc. Roy. Soc. Lond. A 260, 127-138 (1961)
1961
-
[11]
T. H. R. Skyrme, Nucl. Phys. 31, 556-569 (1962)
1962
-
[12]
Manton and P
N. Manton and P. Sutcliffe, Topological Solitons, (Cambridge University Press, Cambridge, 2007)
2007
-
[13]
E. J. Weinberg, Cambridge University Press, 2012, ISBN 978-0-521-11463-9, 978-1-139-57461-7, 978-0-521-11463-9, 978-1- 107-43805-7
2012
-
[14]
Witten, Nucl
E. Witten, Nucl. Phys. B 223, 422-432 (1983)
1983
-
[15]
G. S. Adkins, C. R. Nappi and E. Witten, Nucl. Phys. B 228, 552 (1983)
1983
-
[16]
Bizon and T
P. Bizon and T. Chmaj, Phys. Lett. B 297, 55-62 (1992)
1992
-
[17]
Kleihaus, J
B. Kleihaus, J. Kunz and A. Sood, Phys. Lett. B 352, 247-253 (1995); T. Ioannidou, B. Kleihaus and J. Kunz, Phys. Lett. B 643, 213-220 (2006)
1995
-
[18]
Brihaye and T
Y. Brihaye and T. Delsate, Mod. Phys. Lett. A 21, 2043-2054 (2006)
2006
-
[19]
Sawado, N
N. Sawado, N. Shiiki, K. i. Maeda and T. Torii, Gen. Rel. Grav. 36, 1361-1371 (2004); N. Shiiki and N. Sawado, Phys. Rev. D 71, 104031 (2005); N. Shiiki and N. Sawado, Class. Quant. Grav. 22, 3561-3574 (2005); H. Sato and N. Sawado, Phys. Lett. B 660, 72-79 (2008)
2004
-
[20]
B. M. A. G. Piette and G. I. Probert, Phys. Rev. D 75, 125023 (2007)
2007
-
[21]
J. J. Blanco-Pillado, H. S. Ramadhan and N. Shiiki, Phys. Rev. D 79, 085004 (2009)
2009
-
[22]
Nelmes and B
S. Nelmes and B. M. A. G. Piette, Phys. Rev. D 84, 085017 (2011)
2011
-
[23]
C. Adam, C. Naya, J. Sanchez-Guillen, R. Vazquez and A. Wereszczynski, Phys. Lett. B 742, 136-142 (2015)
2015
-
[24]
Brihaye, C
Y. Brihaye, C. Herdeiro, E. Radu and D. H. Tchrakian, JHEP 11, 037 (2017)
2017
-
[25]
Perapechka and Y
I. Perapechka and Y. Shnir, Phys. Rev. D 95, no.2, 025024 (2017)
2017
-
[26]
B. E. Gunara, F. T. Akbar, R. Fadli, D. M. Akbar and H. Susanto, Adv. Theor. Math. Phys. 25, no.2, 507-541 (2021); B. E. Gunara, E. S. Fadhilla and A. N. Atmaja, Adv. Theor. Math. Phys. 26, no.8, 2667-2695 (2022)
2021
-
[27]
Leask, M
P. Leask, M. Huidobro and A. Wereszczynski, Phys. Rev. D 109, no.5, 056013 (2024)
2024
-
[28]
Canfora and H
F. Canfora and H. Maeda, Phys. Rev. D 87, no.8, 084049 (2013)
2013
-
[29]
Ayon-Beato, F
E. Ayon-Beato, F. Canfora and J. Zanelli, Phys. Lett. B 752, 201-205 (2016)
2016
-
[30]
Ay´ on-Beato, F
E. Ay´ on-Beato, F. Canfora, M. Lagos, J. Oliva and A. Vera, Eur. Phys. J. C 80, no.5, 384 (2020)
2020
-
[31]
Canfora, A
F. Canfora, A. Giacomini, M. Lagos, S. H. Oh and A. Vera, Eur. Phys. J. C 81, no.1, 55 (2021)
2021
-
[32]
Bonga and G
B. Bonga and G. Dotti, Phys. Rev. D 105, no.4, 044049 (2022)
2022
-
[33]
Astorino, F
M. Astorino, F. Canfora, A. Giacomini and M. Ortaggio, Phys. Lett. B 776, 236-241 (2018)
2018
-
[34]
Note that, according to Eq
and [35]) in the context of the SU (2)-NLSM. Note that, according to Eq. (46), the Skyrme field contributes in the same way as the Maxwell field, so that one can define an effective coupling constant and then apply all the results derived in Ref. [36]. B. Thermodynamics The te...
-
[35]
Henr ´ ıquez-B´ aez, M
C. Henr ´ ıquez-B´ aez, M. Lagos and A. Vera, Phys. Rev. D106, no.6, 064027 (2022)
2022
-
[37]
P. D. Alvarez, F. Canfora, N. Dimakis and A. Paliathanasis, Phys. Lett. B 773, 401-407 (2017)
2017
-
[38]
Concha, C
P. Concha, C. Henr ´ ıquez-Baez, E. Rodr ´ ıguez and A. Vera, Phys. Rev. D107, no.12, 124043 (2023)
2023
-
[39]
Canfora, S
F. Canfora, S. Carignano, M. Lagos, M. Mannarelli and A. Vera, Phys. Rev. D 103, no.7, 076003 (2021)
2021
-
[40]
Canfora, Eur
F. Canfora, Eur. Phys. J. C 78, no.11, 929 (2018); F. Canfora, S. H. Oh and A. Vera, Eur. Phys. J. C 79, no.6, 485 (2019); F. Canfora, M. Lagos and A. Vera, Eur. Phys. J. C 80, no.8, 697 (2020)
2018
-
[41]
Abbas, H
G. Abbas, H. Rehman, M. Usama and T. Zhu, Eur. Phys. J. C 83, no.5, 422 (2023)
2023
-
[42]
Canfora, JHEP 11, 007 (2023)
F. Canfora, JHEP 11, 007 (2023)
2023
-
[43]
Al-Badawi, Y
A. Al-Badawi, Y. Sekhmani, J. Rayimbaev and R. Myrzakulov, Int. J. Mod. Phys. D 33, no.12, 2450043 (2024)
2024
-
[44]
Malik, S
A. Malik, S. Chaudhary and A. S. M. Metwally, Eur. Phys. J. C 84, no.6, 610 (2024)
2024
-
[45]
C. G. Huang and C. B. Liang, Phys. Lett. A 201, 27-32 (1995)
1995
-
[46]
J. P. S. Lemos, Phys. Lett. B 353, 46-51 (1995)
1995
-
[47]
Vanzo, Phys
L. Vanzo, Phys. Rev. D 56, 6475-6483 (1997)
1997
-
[48]
R. G. Cai and Y. Z. Zhang, Phys. Rev. D 54, 4891-4898 (1996)
1996
-
[49]
D. R. Brill, J. Louko and P. Peldan, Phys. Rev. D 56, 3600-3610 (1997)
1997
-
[50]
R. B. Mann, Class. Quant. Grav. 14, L109-L114 (1997)
1997
-
[51]
M. M. Caldarelli, A. Christodoulou, I. Papadimitriou and K. Skenderis, JHEP 04 (2017), 001
2017
-
[52]
C. S. Peca and J. P. S. Lemos, J. Math. Phys. 41, 4783-4789 (2000). 12
2000
-
[53]
Anabal´ on, P
A. Anabal´ on, P. Concha, J. Oliva, C. Quijada and E. Rodr ´ ıguez, Phys. Lett. B835, 137521 (2022)
2022
-
[54]
Anabalon, D
A. Anabalon, D. Astefanesei, D. Choque and J. D. Edelstein, JHEP 07, 129 (2020)
2020
-
[55]
Papantonopoulos, Lect
E. Papantonopoulos, Lect. Notes Phys. 828 (2011), 1-438
2011
-
[56]
Bronnikov, N
K. Bronnikov, N. O. Santos and A. Wang, Class. Quant. Grav. 37, no.11, 113002 (2020)
2020
-
[57]
Bertini, S
S. Bertini, S. L. Cacciatori, B. L. Cerchiai, J. Math. Phys. (N.Y.) 47, 043510 (2006)
2006
-
[58]
McInnes, Nucl
B. McInnes, Nucl. Phys. B 989, 116126 (2023)
2023
-
[59]
T. E. Tilma and G. Sudarshan, J. Geom. Phys. 52, 263 (2004)
2004
-
[60]
S. L. Cacciatori, F. Dalla Piazza, and A. Scotti, Trans. Am. Math. Soc. 369, 4709 (2017)
2017
-
[61]
P. D. Alvarez, S. L. Cacciatori, F. Canfora and B. L. Cerchiai, Phys. Rev. D 101, no.12, 125011 (2020)
2020
-
[62]
S. L. Cacciatori and A. Scotti, Universe 8, no.10, 492 (2022)
2022
-
[63]
S. L. Cacciatori, F. Canfora, M. Lagos, F. Muscolino and A. Vera, Nucl. Phys. B 976, 115693 (2022)
2022
-
[64]
S. L. Cacciatori, F. Canfora, M. Lagos, F. Muscolino and A. Vera, JHEP 12, 150 (2021)
2021
-
[65]
G. W. Gibbons and S. W. Hawking, Phys. Rev. D 15, 2738-2751 (1977)
1977
-
[66]
Canfora, A
F. Canfora, A. Gomberoff, M. Lagos and A. Vera, Phys. Rev. D 105, no.8, 084045 (2022)
2022
-
[67]
Flores-Alfonso and H
D. Flores-Alfonso and H. Quevedo, Class. Quant. Grav. 36, 154001 (2019)
2019
-
[68]
Here we show that this formalism can be applied to the toroidal black hole in Eq
and [69]. Here we show that this formalism can be applied to the toroidal black hole in Eq. (14) to get a rotating solution. However, in the present case, there is a subtlety regarding the matter field, which makes our construction different from other rotating black holes in ...
-
[69]
J. D. Brown and J. W. York, Jr., Phys. Rev. D 47 (1993), 1407-1419
1993
-
[70]
Stachel, Phys
J. Stachel, Phys. Rev. D 26, 1281-1290 (1982)
1982
-
[71]
M. A. H. MacCallum, Gen. Rel. Grav. 30, 131-150 (1998)
1998
-
[72]
Erices and C
C. Erices and C. Martinez, Phys. Rev. D 97, no.2, 024034 (2018)
2018
-
[73]
C´ ardenas, O
M. C´ ardenas, O. Fuentealba, C. Mart ´ ınez and R. Troncoso, JHEP02, 058 (2023)
2023
Reviewed August 11, 2026 · model on record in the stance chip above.
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