REVIEW
Separation of gravitational perturbations of singly spinning Myers-Perry black holes
High Energy Physics - Theory · Submitted 13 Oct 2026 · 27 references
Pith's verdict: Major advance in separating gravitational perturbations of higher-dimensional rotating black holes; well-supported and opens a new path for quasinormal mode computations.
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Referee report
The paper
The paper claims
Gravitational perturbations of a higher-dimensional rotating black hole separate, despite coupling between polarisations.
The reading
What carries the argument
Two commuting second-order angular operators $K_C$ and $K_3$ acting on the triple of curvature components $(\Psi_0, \bar\Psi_0, \Phi_{00})$. These operators are independent of the radial coordinate and satisfy a polynomial relation $F(K_C,K_3)=0$ that defines the joint spectrum. They extend the angular Teukolsky operator by coupling the base curvature to the warp component of the transverse sphere. The radial problem is organised by a first-order system of two physical relations that reduce the four apparent integration constants to two, matching the physical degrees of freedom.
Extended reading notes
Core claim
The paper establishes that scalar gravitational perturbations of a singly spinning Myers–Perry black hole, when restricted to the sector invariant under rotations of the transverse $S^{d-4}$, admit a complete separation of variables. Despite the known obstruction to a decoupled Teukolsky equation, two commuting second-order angular operators $K_C$ and $K_3$ are found that act on the triple of gauge-invariant curvature components $\Omega = (\Psi_0, \bar\Psi_0, \Phi_{00})$. Their joint eigenfunctions define an angular harmonic that fixes the relative profiles of the three components. The radial dynamics then reduce to a $2\times 2$ first-order system, equivalent to a single second-order equation, with two physical integration constants. This separation allows the bar-mode and ultraspinning instabilities to be studied via ordinary differential equations alone. The author computes the bar-mode quasinormal spectrum in $d=5,6,7$ and the growing axisymmetric modes in $d=6,\ldots,9$, recovering and in some cases improving on previous PDE results.
Load-bearing premise
The analysis assumes that the three gauge-invariant curvature components form a closed system under the Newman–Penrose and Codazzi identities when restricted to the sector invariant under rotations of the transverse sphere, and that no additional curvature components couple into this system.
Editorial extensions
If this is right
- The bar-mode instability onset in $d=6,7$ can be computed to high precision with a laptop, enabling systematic parameter scans that were previously expensive.
- The growth rates and onset rotations of the axisymmetric ultraspinning instability are obtained for $d=6,\ldots,9$, revealing a turnover in the growth rate for $d=7,8,9$ that was not previously resolved.
- The separated form provides a clean framework for mode stability analysis in higher dimensions, analogous to Whiting's construction for Kerr.
- The angular operators $K_C$ and $K_3$ suggest a hidden symmetry structure in the linearised Einstein equations that may extend to other sectors or more general backgrounds.
Reading between the lines
- The existence of two commuting angular operators indicates that the linearised Einstein equations in this sector possess a hidden symmetry algebra, possibly related to a principal Killing–Yano tensor. Identifying this covariant origin could unify the separation properties observed here with those for test fields.
- The separated radial equations are suitable for studying the nonlinear evolution of instabilities via perturbation theory, and may inform the endpoint of the ultraspinning instability in higher dimensions.
- The method could be extended to multiply spinning Myers–Perry black holes or to include a cosmological constant, provided an analogous invariant sector exists.
Original abstract
Gravitational perturbations of rotating black holes in higher dimensions generally obey coupled partial differential equations. We show that scalar gravitational perturbations invariant under rotations of the transverse sphere of a singly spinning Myers-Perry black hole separate, despite the obstruction to a decoupled Teukolsky equation. Two commuting, second-order angular operators organise the three gauge-invariant curvature components into joint eigenfunctions. The physical radial problem is a $2\times2$ first-order system, equivalent to a single second-order equation. This gives a separation of the sector containing both the bar-mode and axisymmetric ultraspinning instabilities. Using only ordinary differential equations, we compute the bar-mode quasinormal spectrum in $d=5,6,7$ and find instability onsets at $a/r_+=0.90498$ and $0.83228$ in $d=6,7$. We also compute the growing axisymmetric modes and their onset rotations in $d=6,\ldots,9$. The construction shows how separability can survive the coupling between gravitational polarisations.
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.
The abstract, sentence by sentence
Gravitational perturbations of rotating black holes in higher dimensions generally obey coupled partial differential equations. We show that scalar gravitational perturbations invariant under rotations of the transverse sphere of a singly spinning Myers-Perry black hole separate, despite the obstruction to a decoupled Teukolsky equation. Two commuting, second-order angular operators organise the three gauge-invariant curvature components into joint eigenfunctions. The physical radial problem is a $2\times2$ first-order system, equivalent to a single second-order equation. This gives a separation of the sector containing both the bar-mode and axisymmetric ultraspinning instabilities. Using only ordinary differential equations, we compute the bar-mode quasinormal spectrum in $d=5,6,7$ and find instability onsets at $a/r_+=0.90498$ and $0.83228$ in $d=6,7$. We also compute the growing axisymmetric modes and their onset rotations in $d=6,\ldots,9$. The construction shows how separability can survive the coupling between gravitational polarisations.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | Gravitational perturbations of rotating black holes in higher dimensions generally obey coupled partial differential equations. | background 1.00 | 0.06 | 0.03 | asserted 0.90 |
| s1 | We show that scalar gravitational perturbations invariant under rotations of the transverse sphere of a singly spinning Myers-Perry black hole separate, despite the obstruction to a decoupled Teukolsky equation. | result 0.66 | 0.96 | 0.84 | asserted 1.00 |
| s2 | Two commuting, second-order angular operators organise the three gauge-invariant curvature components into joint eigenfunctions. | method 0.87 | 0.89 | 0.13 | asserted 1.00 |
| s3 | The physical radial problem is a $2\times2$ first-order system, equivalent to a single second-order equation. | result 0.55 | 0.82 | 0.10 | asserted 1.00 |
| s4 | This gives a separation of the sector containing both the bar-mode and axisymmetric ultraspinning instabilities. | result 0.49 | 0.73 | 0.20 | asserted 1.00 |
| s5 | Using only ordinary differential equations, we compute the bar-mode quasinormal spectrum in $d=5,6,7$ and find instability onsets at $a/r_+=0.90498$ and $0.83228$ in $d=6,7$. | result 0.95 | 0.97 | 0.14 | asserted 1.00 |
| s6 | We also compute the growing axisymmetric modes and their onset rotations in $d=6,\ldots,9$. | result 0.84 | 0.96 | 0.06 | asserted 1.00 |
| s7 | The construction shows how separability can survive the coupling between gravitational polarisations. | interpretation 1.00 | 0.81 | 0.30 | asserted 1.00 |
What was examined, and what was not
- arXiv listing abstract v1
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Figures
Figures reproduced from arXiv:2610.18956 by the authors.
References
Discussion
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