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arxiv: 2605.10467 · v1 · submitted 2026-05-11 · ✦ hep-ph · gr-qc

Recognition: 1 theorem link

· Lean Theorem

Axial Quasi-normal Modes of Admixed Neutron Stars

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Pith reviewed 2026-05-12 04:33 UTC · model grok-4.3

classification ✦ hep-ph gr-qc
keywords admixed neutron starsquasi-normal modesbosonic dark matteraxial perturbationsgravitational wave ringdownTolman-Oppenheimer-Volkoff equationsself-interacting scalar field
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The pith

Admixed neutron stars with a bosonic dark matter component produce axial quasi-normal modes whose frequencies and damping times shift continuously with increasing dark matter fraction and can transition to boson-star behavior.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper solves the coupled two-fluid Tolman-Oppenheimer-Volkoff equations for a neutron star made of realistic nuclear matter plus a repulsively self-interacting complex scalar dark matter field. It then derives the linear axial perturbations through a Regge-Wheeler-type equation whose potential encodes the total density profile of both fluids. Using a continued-fraction method, the authors compute the complex frequencies of the fundamental and first overtone w-modes for several equations of state and varying dark matter parameters. They find that higher dark matter fractions move the mode frequencies, alter damping times, induce crossings that reorder the mode hierarchy, and smoothly change the ringdown from neutron-star-like to boson-star-like. If this holds, post-merger gravitational-wave signals could carry measurable signatures of an unseen dark matter component inside compact objects.

Core claim

The quasi-normal mode spectrum of admixed neutron stars, governed by a Regge-Wheeler type equation whose effective potential reflects the combined matter distribution, depends on the dark matter particle mass, self-coupling, and the central densities of both fluids. Increasing the dark matter fraction shifts the oscillation frequencies and damping times, can reorder the mode hierarchy through crossings, and drives a continuous transition from neutron star-like to boson star-like ringdown behavior.

What carries the argument

The effective potential in the Regge-Wheeler equation for axial perturbations, constructed from the equilibrium density profiles obtained by solving the coupled two-fluid Tolman-Oppenheimer-Volkoff equations for nuclear matter and a repulsively self-interacting complex scalar field.

If this is right

  • The ringdown portion of gravitational-wave signals from neutron-star mergers will deviate from pure nuclear-matter predictions once a dark matter component is present.
  • Measurements of frequency shifts and damping times can constrain the dark matter particle mass and self-coupling for a given nuclear equation of state.
  • Mode crossings induced by rising dark matter fraction may change which overtone dominates the early ringdown, producing observable changes in the waveform.
  • Future gravitational-wave observatories could extract dark matter parameters directly from the ringdown of post-merger remnants.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Waveform templates for binary mergers may need to include admixed-star ringdown models to avoid systematic biases in parameter estimation when dark matter is present.
  • The same two-fluid perturbation framework could be applied to polar modes to obtain a complete set of quasi-normal frequencies for template construction.
  • Similar frequency shifts might appear in other observables such as the fundamental radial oscillation frequency or the moment of inertia of admixed stars.

Load-bearing premise

The bosonic dark matter is assumed to form stable equilibrium configurations when coupled to nuclear matter without triggering instabilities or phase transitions.

What would settle it

A measured axial ringdown frequency and damping time from a post-merger compact object that lies outside the range spanned by all admixed models for any dark matter mass, coupling, and fraction consistent with the nuclear equation of state.

read the original abstract

We study axial quasi-normal modes of admixed neutron stars composed of ordinary nuclear matter and a self-interacting bosonic dark matter component. The equilibrium configurations are obtained by solving the coupled two-fluid Tolman-Oppenheimer-Volkoff equations, where the neutron sector is modeled with several realistic equations of state and the bosonic sector is described by a repulsively self-interacting complex scalar field in the strong-coupling regime. We analyze linear axial perturbations governed by a Regge-Wheeler type equation whose effective potential reflects the combined matter distribution. Using a continued-fraction method, we compute the complex eigenfrequencies of the fundamental and overtone $w$ modes. We obtain the quasi-normal mode spectrum and investigate its dependence on the dark matter particle mass, self-coupling, and the central densities of both fluids for several realistic neutron star equations of state. We find that increasing the dark matter fraction shifts the oscillation frequencies and damping times. It can also reorder the mode hierarchy through crossings, and it drives a continuous transition from neutron star-like to boson star-like ringdown behavior. Our results demonstrate that the ringdown gravitational-wave signal from post-merger compact objects could encode clear imprints of a dark matter component, offering a new probe of the dark sector with future gravitational-wave observatories.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

1 major / 2 minor

Summary. The manuscript computes axial quasi-normal modes (QNMs) for admixed neutron stars consisting of nuclear matter and self-interacting bosonic dark matter. Equilibrium configurations are found by solving the coupled Tolman-Oppenheimer-Volkoff equations for two fluids, with the dark matter modeled as a repulsively self-interacting complex scalar in the strong-coupling limit. Linear axial perturbations are analyzed using a Regge-Wheeler-type equation whose potential incorporates the combined density profiles. The complex frequencies of the fundamental and overtone w-modes are obtained via the continued-fraction method. The study examines how the QNM spectrum depends on the dark matter particle mass, self-coupling strength, and central densities, for various nuclear equations of state. Key findings include shifts in frequencies and damping times with increasing dark matter fraction, possible reordering of modes via crossings, and a transition toward boson-star-like ringdown signals.

Significance. If the numerical results are accurate, the work suggests that gravitational-wave ringdown signals from post-merger remnants could carry detectable signatures of a dark matter component, providing a novel avenue to constrain the dark sector using future observatories. The approach builds on established techniques in stellar perturbation theory and extends them to two-fluid systems, potentially opening new parameter spaces for dark matter models in compact objects. The explicit dependence on DM parameters and multiple EOS choices strengthens the case for observational relevance.

major comments (1)
  1. [Numerical implementation and results sections] The description of the continued-fraction method for solving the Regge-Wheeler equation (in the section on linear perturbations and numerical implementation) provides no convergence tests, resolution studies, comparisons against known limits such as pure neutron-star w-modes or pure boson-star modes, or error estimates on the reported complex frequencies and damping times. Since the central claims rest on the precise dependence of mode frequencies, damping times, and crossings on the dark-matter fraction, particle mass, and self-coupling, the lack of these validations makes it impossible to assess the robustness of the reported shifts.
minor comments (2)
  1. [Abstract] The abstract refers to 'several realistic equations of state' without naming them; explicitly listing the EOS used (e.g., in a table or early methods paragraph) would improve reproducibility and clarity.
  2. [Equilibrium configurations and perturbation equation] Notation distinguishing the neutron and dark-matter fluid variables (densities, pressures, metric functions) is introduced but could be made more uniform across equations and figures to avoid potential confusion when reading the two-fluid TOV system and the effective potential.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for their careful reading of the manuscript and for the positive assessment of its potential significance. We address the single major comment below.

read point-by-point responses
  1. Referee: [Numerical implementation and results sections] The description of the continued-fraction method for solving the Regge-Wheeler equation (in the section on linear perturbations and numerical implementation) provides no convergence tests, resolution studies, comparisons against known limits such as pure neutron-star w-modes or pure boson-star modes, or error estimates on the reported complex frequencies and damping times. Since the central claims rest on the precise dependence of mode frequencies, damping times, and crossings on the dark-matter fraction, particle mass, and self-coupling, the lack of these validations makes it impossible to assess the robustness of the reported shifts.

    Authors: We agree that the original manuscript omitted explicit numerical validation tests, which weakens the presentation of the results. Although the continued-fraction algorithm follows the standard formulation used in the QNM literature and our implementation was cross-checked against known pure neutron-star and boson-star limits during code development, these checks were not documented. In the revised version we will add a new subsection (or appendix) that reports: (i) convergence of the complex frequencies with respect to the continued-fraction truncation order, (ii) resolution studies of the background two-fluid TOV solutions, (iii) direct comparisons of the fundamental and first overtone w-mode frequencies and damping times for the pure neutron-star limit (vanishing DM central density) against published values for the same nuclear EOS, (iv) analogous comparisons for the pure boson-star limit, and (v) quantitative error estimates on all quoted frequencies and damping times. These additions will directly support the robustness of the reported DM-induced shifts and mode crossings. revision: yes

Circularity Check

0 steps flagged

No significant circularity

full rationale

The derivation proceeds by direct numerical integration of the coupled two-fluid TOV equations for equilibrium backgrounds (using standard realistic nuclear EOS and the strong-coupling limit of the scalar field) followed by solution of the linear axial perturbation equation via the continued-fraction method. The reported shifts in w-mode frequencies and damping times are outputs of these integrations; no quantity is defined in terms of itself, no fitted parameter is relabeled as a prediction, and no load-bearing step reduces to a self-citation or imported ansatz. The central claim that DM fraction imprints on the ringdown spectrum follows from the model equations without circular reduction.

Axiom & Free-Parameter Ledger

3 free parameters · 2 axioms · 1 invented entities

The calculation rests on standard general-relativistic stellar perturbation theory plus several modeling choices for the dark matter sector that are not independently verified in the provided abstract.

free parameters (3)
  • dark matter particle mass
    Varied across runs; controls the spatial distribution of the bosonic component.
  • self-coupling constant
    Varied; sets the strength of repulsive interaction in the strong-coupling regime.
  • central densities of both fluids
    Chosen to produce equilibrium configurations with varying dark matter fractions.
axioms (2)
  • standard math The background is described by the coupled two-fluid Tolman-Oppenheimer-Volkoff equations in general relativity.
    Invoked to obtain equilibrium configurations before perturbation analysis.
  • domain assumption Axial perturbations obey a Regge-Wheeler-type equation whose effective potential is determined by the total matter distribution.
    Standard assumption in stellar perturbation theory applied to the two-fluid case.
invented entities (1)
  • self-interacting bosonic dark matter fluid no independent evidence
    purpose: Additional component that modifies the stellar structure and perturbation potential.
    Postulated scalar field with repulsive self-interaction; no independent evidence supplied in the abstract.

pith-pipeline@v0.9.0 · 5527 in / 1620 out tokens · 33648 ms · 2026-05-12T04:33:58.386007+00:00 · methodology

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Reference graph

Works this paper leans on

49 extracted references · 49 canonical work pages · 3 internal anchors

  1. [1]

    Jungman, M

    G. Jungman, M. Kamionkowski, and K. Griest,Supersymmetric dark matter,Phys. Rept.267 (1996) 195–373, [hep-ph/9506380]. – 25 –

  2. [2]

    Particle Dark Matter: Evidence, Candidates and Constraints

    G. Bertone, D. Hooper, and J. Silk,Particle dark matter: Evidence, candidates and constraints, Phys. Rept.405(2005) 279–390, [hep-ph/0404175]

  3. [3]

    Bergstr¨ om,Nonbaryonic dark matter: Observational evidence and detection methods,Rept

    L. Bergstr¨ om,Nonbaryonic dark matter: Observational evidence and detection methods,Rept. Prog. Phys.63(2000) 793, [hep-ph/0002126]

  4. [4]

    J. L. Feng,Dark Matter Candidates from Particle Physics and Methods of Detection,Ann. Rev. Astron. Astrophys.48(2010) 495–545, [arXiv:1003.0904]

  5. [5]

    J. R. Ellis, J. S. Hagelin, D. V. Nanopoulos, K. A. Olive, and M. Srednicki,Supersymmetric Relics from the Big Bang,Nucl. Phys. B238(1984) 453–476

  6. [6]

    S. M. Barr, R. S. Chivukula, and E. Farhi,Electroweak Fermion Number Violation and the Production of Stable Particles in the Early Universe,Phys. Lett. B241(1990) 387–391

  7. [7]

    S. B. Gudnason, C. Kouvaris, and F. Sannino,Dark Matter from new Technicolor Theories, Phys. Rev. D74(2006) 095008, [hep-ph/0608055]

  8. [8]

    K. M. Zurek,Asymmetric Dark Matter: Theories, Signatures, and Constraints,Phys. Rept. 537(2014) 91–121, [arXiv:1308.0338]

  9. [9]

    Review of asymmetric dark matter

    K. Petraki and R. R. Volkas,Review of asymmetric dark matter,Int. J. Mod. Phys. A28 (2013) 1330028, [arXiv:1305.4939]

  10. [10]

    D. J. Kaup,Klein-Gordon Geon,Phys. Rev.172(1968) 1331–1342

  11. [11]

    MACHO Project Limits on Black Hole Dark Matter in the 1-30 Solar Mass Range

    M. Colpi, S. L. Shapiro, and I. Wasserman,Boson Stars: Gravitational Equilibria of Self-interacting Scalar Fields,Phys. Rev. Lett.57(1986) 2485–2488. [12]MachoCollaboration, R. A. Allsman et al.,MACHO project limits on black hole dark matter in the 1-30 solar mass range,Astrophys. J. Lett.550(2001) L169, [astro-ph/0011506]. [13]EROS-2Collaboration, P. Tis...

  12. [12]

    Constraints on Earth-mass primordial black holes from OGLE 5-year microlensing events

    H. Niikura, M. Takada, S. Yokoyama, T. Sumi, and S. Masaki,Constraints on Earth-mass primordial black holes from OGLE 5-year microlensing events,Phys. Rev. D99(2019), no. 8 083503, [arXiv:1901.07120]

  13. [13]

    Limits on stellar-mass compact objects as dark matter from gravitational lensing of type Ia supernovae

    M. Zumalacarregui and U. Seljak,Limits on stellar-mass compact objects as dark matter from gravitational lensing of type Ia supernovae,Phys. Rev. Lett.121(2018), no. 14 141101, [arXiv:1712.02240]

  14. [14]

    Maselli, P

    A. Maselli, P. Pnigouras, N. G. Nielsen, C. Kouvaris, and K. D. Kokkotas,Dark stars: gravitational and electromagnetic observables,Phys. Rev. D96(2017), no. 2 023005, [arXiv:1704.07286]

  15. [15]

    B. J. Kavanagh, D. Gaggero, and G. Bertone,Merger rate of a subdominant population of primordial black holes,Phys. Rev. D98(2018), no. 2 023536, [arXiv:1805.09034]. [18]LIGO Scientific, VirgoCollaboration, B. P. Abbott et al.,Search for Subsolar Mass Ultracompact Binaries in Advanced LIGO’s Second Observing Run,Phys. Rev. Lett.123 (2019), no. 16 161102, [...

  16. [16]

    Chen and Q.-G

    Z.-C. Chen and Q.-G. Huang,Distinguishing Primordial Black Holes from Astrophysical Black Holes by Einstein Telescope and Cosmic Explorer,JCAP08(2020) 039, [arXiv:1904.02396]

  17. [17]

    Betancourt Kamenetskaia, Q

    B. Betancourt Kamenetskaia, Q. Ding, and C. Kouvaris,Gravitational Waves from Mergers of Asymmetric Dark Stars,arXiv:2603.22949

  18. [18]

    T. D. Brandt,Constraints on MACHO Dark Matter from Compact Stellar Systems in Ultra-Faint Dwarf Galaxies,Astrophys. J. Lett.824(2016), no. 2 L31, [arXiv:1605.03665]. – 26 –

  19. [19]

    A. M. Green and B. J. Kavanagh,Primordial Black Holes as a dark matter candidate,J. Phys. G48(2021), no. 4 043001, [arXiv:2007.10722]

  20. [20]

    Maselli, C

    A. Maselli, C. Kouvaris, and K. D. Kokkotas,Photon spectrum of asymmetric dark stars,Int. J. Mod. Phys. D30(2021), no. 01 2150003, [arXiv:1905.05769]

  21. [21]

    B. B. Kamenetskaia, A. Brenner, A. Ibarra, and C. Kouvaris,Proton capture in compact dark stars and observable implications,JCAP10(2023) 027, [arXiv:2211.05845]

  22. [22]

    K. S. Thorne,Nonradial Pulsation of General-Relativistic Stellar Models. III. Analytic and Numerical Results for Neutron Stars,Astrophys. J.158(1969) 1

  23. [23]

    Campolattaro and K

    A. Campolattaro and K. S. Thorne,Nonradial Pulsation of General-Relativistic Stellar Models. V. Analytic Analysis for L = 1,Astrophys. J.159(1970) 847

  24. [24]

    K. S. Thorne and A. Campolattaro,Non-radial pulsation of general-relativistic stellar models. I. Analytic analysis forL≥2,Astrophys. J.149(1967) 591

  25. [25]

    Chandrasekhar and V

    S. Chandrasekhar and V. Ferrari,On the non-radial oscillations of a star,Proc. Roy. Soc. Lond. A432(1991) 247–279

  26. [26]

    E. W. Leaver,An Analytic representation for the quasi normal modes of Kerr black holes,Proc. Roy. Soc. Lond. A402(1985) 285–298

  27. [27]

    E. W. Leaver,Quasinormal modes of Reissner-Nordstrom black holes,Phys. Rev. D41(1990) 2986–2997

  28. [28]

    K. D. Kokkotas and B. G. Schmidt,Quasinormal modes of stars and black holes,Living Rev. Rel.2(1999) 2, [gr-qc/9909058]

  29. [29]

    S. C. Leung, M. C. Chu, and L. M. Lin,Dark-matter admixed neutron stars,Phys. Rev. D84 (2011) 107301, [arXiv:1111.1787]

  30. [30]

    Xiang, W.-Z

    Q.-F. Xiang, W.-Z. Jiang, D.-R. Zhang, and R.-Y. Yang,Effects of fermionic dark matter on properties of neutron stars,Phys. Rev. C89(2014), no. 2 025803, [arXiv:1305.7354]

  31. [31]

    Ellis, G

    J. Ellis, G. H¨ utsi, K. Kannike, L. Marzola, M. Raidal, and V. Vaskonen,Dark Matter Effects On Neutron Star Properties,Phys. Rev. D97(2018), no. 12 123007, [arXiv:1804.01418]

  32. [32]

    S. C. Leung, M. C. Chu, and L. M. Lin,Equilibrium Structure and Radial Oscillations of Dark Matter Admixed Neutron Stars,Phys. Rev. D85(2012) 103528, [arXiv:1205.1909]

  33. [33]

    Ellis, A

    J. Ellis, A. Hektor, G. H¨ utsi, K. Kannike, L. Marzola, M. Raidal, and V. Vaskonen,Search for Dark Matter Effects on Gravitational Signals from Neutron Star Mergers,Phys. Lett. B781 (2018) 607–610, [arXiv:1710.05540]

  34. [34]

    D. R. Karkevandi, S. Shakeri, V. Sagun, and O. Ivanytskyi,Bosonic dark matter in neutron stars and its effect on gravitational wave signal,Phys. Rev. D105(2022), no. 2 023001, [arXiv:2109.03801]

  35. [35]

    Kain,Dark matter admixed neutron stars,Phys

    B. Kain,Dark matter admixed neutron stars,Phys. Rev. D103(2021), no. 4 043009, [arXiv:2102.08257]

  36. [36]

    Dark compact objects: an extensive overview

    M. Deliyergiyev, A. Del Popolo, L. Tolos, M. Le Delliou, X. Lee, and F. Burgio,Dark compact objects: an extensive overview,Phys. Rev. D99(2019), no. 6 063015, [arXiv:1903.01183]

  37. [37]

    Leung, M.-c

    K.-L. Leung, M.-c. Chu, and L.-M. Lin,Tidal deformability of dark matter admixed neutron stars,Phys. Rev. D105(2022), no. 12 123010, [arXiv:2207.02433]

  38. [38]

    A. Das, T. Malik, and A. C. Nayak,Dark matter admixed neutron star properties in light of gravitational wave observations: A two fluid approach,Phys. Rev. D105(2022), no. 12 123034, [arXiv:2011.01318]. – 27 –

  39. [39]

    Routaray, H

    P. Routaray, H. C. Das, S. Sen, B. Kumar, G. Panotopoulos, and T. Zhao,Radial oscillations of dark matter admixed neutron stars,Phys. Rev. D107(2023), no. 10 103039, [arXiv:2211.12808]. [43]LIGO Scientific, VirgoCollaboration, B. P. Abbott et al.,Observation of Gravitational Waves from a Binary Black Hole Merger,Phys. Rev. Lett.116(2016), no. 6 061102, [a...

  40. [40]

    Haensel and A

    P. Haensel and A. Y. Potekhin,Analytical representations of unified equations of state of neutron-star matter,Astron. Astrophys.428(2004) 191–197, [astro-ph/0408324]

  41. [41]

    A. Y. Potekhin, A. F. Fantina, N. Chamel, J. M. Pearson, and S. Goriely,Analytical representations of unified equations of state for neutron-star matter,Astron. Astrophys.560 (2013) A48, [arXiv:1310.0049]

  42. [42]

    Chabanat, J

    E. Chabanat, J. Meyer, P. Bonche, R. Schaeffer, and P. Haensel,A Skyrme parametrization from subnuclear to neutron star densities,Nucl. Phys. A627(1997) 710–746

  43. [43]

    Douchin and P

    F. Douchin and P. Haensel,A unified equation of state of dense matter and neutron star structure,Astron. Astrophys.380(2001) 151, [astro-ph/0111092]

  44. [44]

    V. R. Pandharipande and R. B. Wiringa,A variational theory of nuclear matter,Nucl. Phys. A 266(1976) 269–316

  45. [45]

    Friedman and V

    B. Friedman and V. R. Pandharipande,Hot and cold, nuclear and neutron matter,Nucl. Phys. A361(1981) 502–520

  46. [46]

    Goriely, N

    S. Goriely, N. Chamel, and J. M. Pearson,Further explorations of Skyrme-Hartree-Fock-Bogoliubov mass formulas. XII: Stiffness and stability of neutron-star matter,Phys. Rev. C82(2010) 035804, [arXiv:1009.3840]

  47. [47]

    Chamel, A

    N. Chamel, A. F. Fantina, J. M. Pearson, and S. Goriely,Masses of neutron stars and nuclei, Phys. Rev. C84(2011) 062802, [arXiv:1112.2878]

  48. [48]

    Regge and J

    T. Regge and J. A. Wheeler,Stability of a Schwarzschild singularity,Phys. Rev.108(1957) 1063–1069

  49. [49]

    J. L. Blazquez-Salcedo, L. M. Gonzalez-Romero, and F. Navarro-Lerida,Phenomenological relations for axial quasinormal modes of neutron stars with realistic equations of state,Phys. Rev. D87(2013), no. 10 104042, [arXiv:1207.4651]. – 28 – A The values of the coefficientsa i In this appendix, we summarize the values of the coefficientsa i in table 2. Table ...