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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.

T0 · AI review

How this review was made: An AI referee (deepseek/deepseek-v4-flash) read the paper on October 15, 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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  3. T2 Compute The paper's code or calculations re-run with the same results.
  4. T3 Formal statement The claims written out in a formal math language a computer can read.
  5. T4 Proof Those claims proved, and the proof checked by computer.

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arXiv ID2610.18956 (version 1)
Pith IDWQBST724, Pith's permanent record of this paper and its review
CitationJorge E. Santos. "Separation of gravitational perturbations of singly spinning Myers-Perry black holes." arXiv:2610.18956 (2026). https://pith.science/paper/WQBST724
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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

This paper shows that gravitational perturbations of a singly spinning Myers–Perry black hole can be separated into ordinary differential equations in the sector invariant under rotations of the transverse sphere. This sector contains both the bar-mode and axisymmetric ultraspinning instabilities. The separation is achieved by constructing two commuting angular operators that organise the three gauge-invariant curvature components into joint eigenfunctions. The radial problem reduces to a single second-order equation, similar in complexity to the four-dimensional Teukolsky equation, even though the components remain coupled. This provides a practical method to compute quasinormal spectra and instability onsets using only ODEs, which the author demonstrates for dimensions five through nine.

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

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

  • 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.

Compiled by classifier-1.13.0 via TypeSafe API, question bank abstract-p1-20260923, 2026-10-15: 1 request, 6,253 input tokens.

What the abstract itself states, as probabilities: claims first 0.06 · states limitation 0.50 · human participants 0.01 · controlled comparison 0.02 · randomized assignment 0.01 · states quantitative result 0.98 · compares with prior results 0.26 · mentions code or data availability 0.02.

The abstract, sentence by sentence

arXiv listing abstract v1. Results and the main claim are underlined; .

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

What the classifier reports for each sentence. The number is the probability it gave the label.
#sentencerolethe authors' own workstates the main conclusionstrength
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 kind of paper the classifier reports this is: theoretical result 0.97 · evidence from proof or derivation 0.65.

What was examined, and what was not

sources read
  • arXiv listing abstract v1
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

Figures
Figure 1. FIG. 1. Real (a) and imaginary (b) parts of the
Figure 2. shows the growth rates as functions of a/r+. Extrapolating from γr+ ≲ 3 × 10−3 gives the onsets in Table II. To compare with the original ultraspinning thresholds [20], we convert to a/r0 = x(1 + x 2 ) −1/(n+1) , where x = a/r+ and r0 is defined below Eq. (1). In d = 7, 8, 9 this recovers the stationary zero modes to all quoted digits. In d = 6 the onsets are about 1% lower. Although this exceeds the earlier quoted error estimate, it likely reflects numerical error in the PDE calculation, whose stability and accuracy in d = 6 were particularly sensitive to the asymptotic fall-off

Figures reproduced from arXiv:2610.18956 by the authors.

References

Discussion

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