Pith. sign in

REVIEW 4 major objections 4 minor 42 references

$f$-Mode oscillations and the gravitational response of compact stars with analytic equations of state

T0 review · 4 major / 4 minor · reviewed 2026-08-03 · deepseek-v4-flash

Pith's one-line read Analytic equations of state from holographic quark matter and scalar dark matter can reproduce realistic compact-star f-mode oscillations.

desk verdict Standard machinery applied to two analytic EOSs, but an inconsistent equation in the appendix makes the f-mode results unverifiable. read the letter →

arxiv 2601.21911 v2 pith:LYZ3J4TP submitted 2026-01-29 hep-ph astro-ph.HEastro-ph.SRgr-qc

classification hep-phastro-ph.HEastro-ph.SRgr-qc
keywords compactstarsequationsofstateholographicQCDself-interactingdarkmatterf-modeoscillationstidaldeformabilitygravitational-waveasteroseismologyrelativisticstellarstructure
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

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

The reading

The paper aims to show that two closed-form, analytic equations of state — one derived from a holographic description of dense quark matter and one from a self-interacting scalar dark-matter model — can serve as complete descriptions of compact stars. Solving the relativistic stellar-structure equations with these EOSs yields mass-radius curves, tidal deformabilities, and f-mode oscillation frequencies and damping times in a single self-consistent calculation. The central new claim is that f-mode frequencies depend mainly on the star's average density, following roughly its square root, while damping times follow simple combinations of mass and radius. If true, this means gravitational-wave asteroseismology can extract dense-matter information from analytic models quickly, and the same pipeline can be applied to any analytic equation of state.

What carries the argument

A pair of closed-form barotropic equations of state — one from an instanton-gas approximation in a confining holographic model (Eq. 2.1) and one from a self-interacting scalar-field model that also has a holographic quark-core interpretation (Eq. 2.3). These are integrated in the relativistic stellar-structure equations from the center to p=0, then fed into two perturbation problems: a first-order Riccati equation for the tidal Love number and a four-function linear system for nonradial oscillations with purely outgoing waves at infinity. The main output is the f-mode frequency scaling with the square root of average density.

What would settle it

A post-merger gravitational-wave measurement of a compact star's f-mode frequency, mass, and radius that falls outside the predicted sqrt(average-density) band would contradict the central claim; so would a demonstration that either analytic EOS fails basic low-density nuclear constraints (e.g., saturation density and symmetry energy) that the stars must satisfy.

Watch

Extended reading notes

Core claim

The authors' central discovery claim is that the f-mode frequency of a compact star described by either analytic EOS scales approximately with the square root of the average stellar density, while the damping time is controlled by simple combinations of mass and radius — so the oscillation spectrum is fixed by global stellar properties rather than by the microscopic details of the EOS. They also show that both analytic EOSs produce mass-radius and tidal-deformability curves spanning neutron-star-like and more compact quark-star- or dark-star-like configurations, which they take as evidence that these models are compatible with current multi-messenger constraints and useful for gravitational-

Load-bearing premise

Everything rests on the assumption that each analytic equation of state is complete from the stellar center to the zero-pressure surface, with no crust or low-density nuclear matching; if the EOS is wrong in the outer layers, the computed radii, tidal deformabilities, and f-mode frequencies are not those of real compact stars.

Editorial extensions

If this is right

  • If the scaling holds, f-mode frequencies can be estimated from mass and radius alone, bypassing detailed microphysics.
  • Analytic EOSs enable fast parameter scans for gravitational-wave asteroseismology, since no numerical EOS tables are needed.
  • The same calculation pipeline applies to any analytic equation of state, broadening the set of models that can be confronted with observations.
  • Tidal deformability tracks EOS stiffness, so combined inspiral and post-merger measurements could help identify the underlying microscopic model.
  • Frequency and damping time together provide two independent observables that future gravitational-wave detectors could use to test the same EOSs.

Reading between the lines

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

  • The paper tests only two EOS families; whether the sqrt-density scaling is a genuine quasi-universal relation would need checking against a broader set of analytic and tabulated EOSs.
  • A hybrid test — matching these EOSs to a hadronic low-density EOS and crust — would show how much of the result depends on the no-crust assumption.
  • Feeding these equilibrium models into numerical-relativity merger simulations would test whether post-merger oscillations follow the predicted f-modes.
  • If the scaling survives finite-temperature and rotation extensions, the same pipeline could apply to hot post-merger remnants, not just cold isolated stars.
Share X Bluesky LinkedIn Reddit HN

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Referee Report

4 major / 4 minor

Summary. The paper studies two analytic equations of state: a Witten-Sakai-Sugimoto (WSS) instanton-gas EOS (Eq. 2.1) and a self-interacting dark matter / D3-D7 type EOS (Eq. 2.3). It integrates the TOV equations to obtain mass-radius relations, solves the Hinderer tidal-deformability equation, and computes f-mode oscillation frequencies and damping times using the Lindblom-Detweiler formalism (Appendix A). The central claim, stated in Section 5, is that f-mode asteroseismology is the 'main new result': f-mode frequencies scale approximately with the square root of the average stellar density, and damping times follow simple mass-radius combinations, with analytic EOSs providing a fast route to gravitational-wave parameter scans.

Significance. If correct, the paper would demonstrate that simple analytic EOSs can reproduce realistic compact-star observables, enabling efficient scans of dense-matter parameters. However, the manuscript currently lacks the quantitative support needed to establish this. There are no numerical tables, no code, no comparison to published universal-relation fits or observational constraints (GW170817, NICER), and no validation against known f-mode results for a standard EOS. More seriously, the perturbation equations in Appendix A contain an apparent dimensional inconsistency that puts the f-mode results into question unless corrected and re-verified.

major comments (4)
  1. [Appendix A, Eq. (A.2)] The second algebraic relation for X^{ℓm} contains the term ω^3 (ε+p) e^{-ψ/2} V^{ℓm}. This is inconsistent with the rest of the linearized system, which is second-order in time and therefore contains at most ω^2. Dimensionally, ω^3(ε+p)e^{-ψ/2}V has units of 1/L^8 (for ℓ=2), while the other terms in the same equation have dimensions 1/L^6 and 1/L^4, so the equation as written cannot be correct. If this relation was actually used in the numerical solver, the computed f-mode frequencies and damping times are not physical eigenfrequencies. If it is a transcription error, the printed equations are not self-consistent and the results are not reproducible. The authors should correct this equation, re-run the calculations, and provide a validation check against known results for a standard EOS.
  2. [Sections 4 and 5, Figs. 5-6] The paper claims that f-mode frequency scales as the square root of the average density and that the results follow 'robust trends,' but no quantitative support is given. There are no fits, residuals, or error estimates, and no comparison to the well-known Andersson-Kokkotas empirical relations or to other published f-mode universal relations. Furthermore, the claim that this is the 'main new result' is overstated, as similar scalings have been established for many EOSs. The authors should compare their f-mode curves with existing universal relations and provide a quantitative measure of the scatter.
  3. [Sections 2 and 5] The analytic EOSs are used from the stellar center to the surface with p=0, with no matching to a low-density hadronic EOS or crust. The parameter ranges for ℓ (in Eq. 2.1) and B (in Eq. 2.3) are swept without any independent justification against observational or theoretical constraints. The paper asserts in Section 5 that these EOSs produce configurations 'compatible with current astrophysical constraints,' but no quantitative comparison to GW170817, NICER, or other data is shown. Without such a comparison, the claimed astrophysical relevance is not established.
  4. [Section 4, Eq. (4.1)-(4.5)] The manuscript does not describe the numerical method used to solve the Lindblom-Detweiler equations, nor does it report the number of grid points, convergence criteria, or how the complex eigenfrequency ω is extracted. The only reference is to Appendix A, which itself has the inconsistency noted above. This lack of detail, together with the absence of code or data tables, makes the f-mode results impossible to reproduce or verify. At minimum, the authors should provide a table of f-mode frequencies and damping times for representative parameter values.
minor comments (4)
  1. [Abstract vs. Section 2] The abstract refers to 'neutron stars and quark stars,' while Section 2 describes the second EOS as a 'dark star' (SIDM) model. Please clarify the terminology consistently.
  2. [Figures 2 and 6] The captions refer to 'Eq. (1)' but should refer to Eq. (2.3).
  3. [Eq. (3.8)] The potential is written as φ' in the last term, while the TOV section uses ν(r). Please use a consistent symbol for the metric potential.
  4. [References] Reference [7] is incomplete: it lists authors and title but lacks journal, year, and arXiv identifier. Also, the pointlike EOS in footnote 1 is not used in the main text; consider moving it to the main discussion or deleting it.

Circularity Check

0 steps flagged · score 0.0 of 10

No significant circularity: f-mode outputs are computed from explicitly stated analytic EOSs and independent Lindblom-Detweiler equations; self-citations are inputs/context, not load-bearing reductions.

full rationale

The paper's derivation chain is: (i) adopt two analytic EOSs, Eqs. (2.1) and (2.3), from Refs. [22] and [23]; (ii) solve the TOV equations (2.4)-(2.6); (iii) integrate the tidal equation (3.6) and the f-mode perturbation equations (A.1)-(A.2); (iv) examine f-mode frequencies and damping times as functions of stellar parameters. None of these steps defines the f-mode output in terms of itself, nor fits any parameter to the f-mode data. The EOS parameters ℓ and B are model parameters swept to produce curves, not fitted to the oscillation frequencies, so there is no 'fitted input called prediction.' The central assertion that f-mode frequency scales roughly with the square root of average density is an output of the TOV+perturbation calculation, not imposed as input; the paper is restating a known empirical universal relation, but that is not a circular reduction. The self-citations ([22], [30], [21], etc.) are used as sources for the input EOSs or as background, but the EOSs are explicitly displayed in the paper, and the numerical chain does not depend on an unverified self-cited uniqueness theorem or on quoted results from the same authors in place of calculation. The Lindblom-Detweiler formalism is cited to external literature [37,38]. The suspicious ω^3 factor in Eq. (A.2) is a consistency/reproducibility concern, not a circularity: even if erroneous, it does not make the f-mode result equivalent to its input by construction. Overall, the paper is a conditional parameter scan over analytic EOSs; whether the EOSs are physically realistic or externally valid is a separate question, not a circularity. Score 0.

Assumptions & free parameters 2 free parameters · 5 assumptions · 0 invented entities

The central computation depends on two free EOS parameters (ℓ and B), the validity of two EOSs imported from prior work, and standard general-relativistic stellar-structure and perturbation machinery. No new particles, forces, or conserved quantities are introduced.

free parameters (2)
  • ℓ (D8-D8 brane separation in WSS model) = not fixed; varied to generate the M-R family in Fig. 1
    Appears in Eq. (2.1) through A = 1.8e-5 ℓ^{-7}; the paper scans it to produce different compact-star configurations and gives no independent value from data or theory.
  • B (SIDM / D3-D7 EOS parameter) = not fixed; varied to generate the M-R family in Fig. 2
    B = 0.08 sqrt(λ4) (m/GeV)^2 in Eq. (2.3); the paper treats it as free to span mass-radius curves and does not fit it to observations.
assumptions (5)
  • domain assumption The holographic WSS instanton-gas EOS Eq. (2.1) from ref. [22] is a valid complete barotropic EOS for cold neutron-star matter from center to surface.
    The paper integrates TOV equations using this EOS down to p=0 without matching to a low-density nuclear EOS or crust; its validity at low densities is not demonstrated here.
  • domain assumption The strong-coupling condition λ4 M_PL^2/m^2 >> 1 from ref. [23] holds, so the SIDM scalar field behaves as a perfect fluid with EOS Eq. (2.3).
    Used to justify applying perfect-fluid TOV and Lindblom-Detweiler equations to dark stars; imported from prior work without new evidence in this paper.
  • domain assumption Cold compact stars are barotropic and oscillate adiabatically, p = p(ε).
    Stated in Section 4; excludes temperature, rotation, magnetic fields, and phase-transition dynamics, all of which the paper acknowledges in Section 5.
  • standard math The Lindblom-Detweiler equations (A.1)-(A.2) together with the outgoing-wave boundary condition (A.10) correctly give the quasinormal f-modes.
    This is standard general-relativistic stellar perturbation theory, accepted in the literature and used without modification.
  • standard math TOV equations (2.4)-(2.6) describe the static, spherical equilibrium of a perfect-fluid star.
    Standard general-relativistic stellar structure; not re-derived or questioned in the paper.

how reviews work

0 comments
Cite this review

Pith. "Pith review of $f$-Mode oscillations and the gravitational response of compact stars with analytic equations of state." pith.science (2026). https://pith.science/paper/LYZ3J4TP

@misc{pith2026260121911,
  author       = {Pith},
  title        = {Pith review of: $f$-Mode oscillations and the gravitational response of compact stars with analytic equations of state},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/LYZ3J4TP}},
  note         = {Machine review of arXiv:2601.21911}
}
abstract

We use a simple holographic model to study the property of cold and dense neutron stars (NSs) and deconfined QCD matter. With the aim of investigating the global properties of compact stars, such as the total gravitational mass and radius, the equation of states (EOS) of neutron stars and quark stars (QSs) are used to solve the Tolman-Oppenheimer-Volkov (TOV) equations for stellar structure. Additionally, we investigate the tidal deformabilities and $f$-mode oscillation for these two different compact stars. Our main conclusion is that, by using a holographic equation of state, it is possible to obtain neutron matter and quark matter properties and that it is also possible to extend the procedure to astrophysical applications.

Discussion (0). Continue with ORCID to comment.

Reference graph

Works this paper leans on

42 extracted references · 3 linked inside Pith

  1. [30]

    Fundamental oscillation modes of self-interacting bosonic dark stars,

    C. Vásquez Flores, A. Parisi, C. S. Chen and G. Lugones, “Fundamental oscillation modes of self-interacting bosonic dark stars,” JCAP06(2019), 051

  2. [1]

    Properties of the binary neutron star merger GW170817,

    B. P. Abbottet al.[LIGO Scientific and Virgo], “Properties of the binary neutron star merger GW170817,” Phys. Rev. X9, no.1, 011001 (2019) doi:10.1103/PhysRevX.9.011001 [arXiv:1805.11579 [gr-qc]]

  3. [2]

    Observation of Gravitational Waves from Two Neutron Star–Black Hole Coalescences,

    R. Abbottet al.[LIGO Scientific, KAGRA and VIRGO], “Observation of Gravitational Waves from Two Neutron Star–Black Hole Coalescences,” Astrophys. J. Lett.915(2021) no.1, L5

  4. [3]

    Observation of Gravitational Waves from the Coalescence of a 2.5–4.5M⊙ Compact Object and a Neutron Star,

    A. G. Abacet al.[LIGO Scientific, KAGRA and VIRGO], “Observation of Gravitational Waves from the Coalescence of a 2.5–4.5M⊙ Compact Object and a Neutron Star,” Astrophys. J. Lett.970(2024) no.2, L34

  5. [4]

    Small, dense quark stars from perturbative QCD,

    E. S. Fraga, R. D. Pisarski and J. Schaffner-Bielich, “Small, dense quark stars from perturbative QCD,” Phys. Rev. D63(2001), 121702

  6. [5]

    Merger of compact stars in the two-families scenario,

    R. De Pietri, A. Drago, A. Feo, G. Pagliara, M. Pasquali, S. Traversi and G. Wiktorowicz, “Merger of compact stars in the two-families scenario,” Astrophys. J.881(2019) no.2, 122 – 11 –

  7. [6]

    Phase transition effects on the dynamical stability of hybrid neutron stars,

    J. P. Pereira, C. V. Flores and G. Lugones, “Phase transition effects on the dynamical stability of hybrid neutron stars,” Astrophys. J.860(2018) no.1, 12

  8. [7]

    Hybrid stars in the light of the merging event GW170817,

    A. Parisi, C. Vásquez Flores, C. H. Lenzi, C. S. Chen and G. Lugones, “Hybrid stars in the light of the merging event GW170817,”

Show all 42 references
  1. [8]

    PSR J0030+0451 Mass and Radius fromN ICERData and Implications for the Properties of Neutron Star Matter,

    M. C. Miller, F. K. Lamb, A. J. Dittmann, S. Bogdanov, Z. Arzoumanian, K. C. Gendreau, S. Guillot, A. K. Harding, W. C. G. Ho and J. M. Lattimer,et al.“PSR J0030+0451 Mass and Radius fromN ICERData and Implications for the Properties of Neutron Star Matter,” Astrophys. J. Lett...

  2. [9]

    AN ICERView of PSR J0030+0451: Millisecond Pulsar Parameter Estimation,

    T. E. Riley, A. L. Watts, S. Bogdanov, P. S. Ray, R. M. Ludlam, S. Guillot, Z. Arzoumanian, C. L. Baker, A. V. Bilous and D. Chakrabarty,et al.“AN ICERView of PSR J0030+0451: Millisecond Pulsar Parameter Estimation,” Astrophys. J. Lett.887(2019) no.1, L21

  3. [10]

    Holographic QCD in the NICER era,

    N. Jokela, M. Järvinen and J. Remes, “Holographic QCD in the NICER era,” Phys. Rev. D 105(2022) no.8, 086005

  4. [11]

    Confronting new NICER mass-radius measurements with phase transition in dense matter and twin compact stars,

    J. J. Li, A. Sedrakian and M. Alford, “Confronting new NICER mass-radius measurements with phase transition in dense matter and twin compact stars,” JCAP02(2025), 002

  5. [12]

    QCD and Strongly Coupled Gauge Theories: Challenges and Perspectives,

    N. Brambilla, S. Eidelman, P. Foka, S. Gardner, A. S. Kronfeld, M. G. Alford, R. Alkofer, M. Butenschoen, T. D. Cohen and J. Erdmenger,et al.“QCD and Strongly Coupled Gauge Theories: Challenges and Perspectives,” Eur. Phys. J. C74(2014) no.10, 2981

  6. [13]

    Holographic approach to compact stars and their binary mergers,

    C. Hoyos, N. Jokela and A. Vuorinen, “Holographic approach to compact stars and their binary mergers,” Prog. Part. Nucl. Phys.126(2022), 103972

  7. [14]

    Holographic modeling of nuclear matter and neutron stars,

    M. Järvinen, “Holographic modeling of nuclear matter and neutron stars,” Eur. Phys. J. C82 (2022) no.4, 282

  8. [15]

    Holographic quark matter and neutron stars,

    C. Hoyos, D. Rodríguez Fernández, N. Jokela and A. Vuorinen, “Holographic quark matter and neutron stars,” Phys. Rev. Lett.117(2016) no.3, 032501

  9. [16]

    Holographic compact stars meet gravitational wave constraints,

    E. Annala, C. Ecker, C. Hoyos, N. Jokela, D. Rodríguez Fernández and A. Vuorinen, “Holographic compact stars meet gravitational wave constraints,” JHEP12(2018), 078

  10. [17]

    Compact Star of Holographic Nuclear Matter and GW170817,

    K. Zhang, T. Hirayama, L. W. Luo and F. L. Lin, “Compact Star of Holographic Nuclear Matter and GW170817,” Phys. Lett. B801(2020), 135176

  11. [18]

    Holographic hybrid stars with slow phase transitions,

    M. Aleixo, C. H. Lenzi, M. Dutra, O. Lourenço and W. de Paula, “Holographic hybrid stars with slow phase transitions,” Phys. Rev. D111(2025) no.11, 116012

  12. [19]

    Gravitational waves from holographic neutron star mergers,

    C. Ecker, M. Järvinen, G. Nijs and W. van der Schee, “Gravitational waves from holographic neutron star mergers,” Phys. Rev. D101(2020) no.10, 103006

  13. [20]

    Dark stars: gravitational and electromagnetic observables,

    A. Maselli, P. Pnigouras, N. G. Nielsen, C. Kouvaris and K. D. Kokkotas, “Dark stars: gravitational and electromagnetic observables,” Phys. Rev. D96, no.2, 023005 (2017) doi:10.1103/PhysRevD.96.023005 [arXiv:1704.07286 [astro-ph.HE]]

  14. [21]

    Dark stars and gravitational waves: Topical review,

    K. Zhang, L. W. Luo, J. S. Tsao, C. S. Chen and F. L. Lin, “Dark stars and gravitational waves: Topical review,” Results Phys.53, 106967 (2023) doi:10.1016/j.rinp.2023.106967 [arXiv:2303.03266 [astro-ph.HE]]

  15. [22]

    Deriving neutron star equation of state from AdS/QCD,

    W. Li, J. Y. Wu and K. Zhang, “Deriving neutron star equation of state from AdS/QCD,” Results Phys.64(2024), 107893

  16. [23]

    Boson Stars: Gravitational Equilibria of Selfinteracting Scalar Fields,

    M. Colpi, S. L. Shapiro and I. Wasserman, “Boson Stars: Gravitational Equilibria of Selfinteracting Scalar Fields,” Phys. Rev. Lett.57(1986), 2485-2488

  17. [24]

    Static solutions of Einstein’s field equations for spheres of fluid,

    R. C. Tolman, “Static solutions of Einstein’s field equations for spheres of fluid,” Phys. Rev.55 (1939), 364-373

  18. [25]

    On massive neutron cores,

    J. R. Oppenheimer and G. M. Volkoff, “On massive neutron cores,” Phys. Rev.55(1939), 374-381 – 12 –

  19. [26]

    Andersson and K

    N. Andersson and K. D. Kokkotas, Mon. Not. Roy. Astron. Soc.299, 1059 (1998)

  20. [27]

    C. V. Flores and G. Lugones, Phys. Rev. C95(2017) no.2, 025808

  21. [28]

    C. V. Flores and G. Lugones, JCAP1808(2018) no.08, 046

  22. [29]

    Chirenti, G

    C. Chirenti, G. H. de Souza and W. Kastaun, Phys. Rev. D91(2015) no.4, 044034

  23. [31]

    Detectability of Massive Boson Stars using Gravitational Waves from Fundamental Oscillations,

    S. Shirke, B.K. Pradhan, D. Chatterjee, L. Sagunski and J. S. Bielich, “Detectability of Massive Boson Stars using Gravitational Waves from Fundamental Oscillations,” JCAP01(2026), 017

  24. [32]

    Tidal stabilization of rigidly rotating, fully relativistic neutron stars,

    K. S. Thorne, “Tidal stabilization of rigidly rotating, fully relativistic neutron stars,” Phys. Rev. D58, 124031 (1998) doi:10.1103/PhysRevD.58.124031 [arXiv:gr-qc/9706057 [gr-qc]]

  25. [33]

    Tidal Love numbers of neutron stars,

    T. Hinderer, “Tidal Love numbers of neutron stars,” Astrophys. J.677(2008), 1216-1220 [erratum: Astrophys. J.697(2009) no.1, 964]

  26. [34]

    Tidal Love Numbers of Neutron and Self-Bound Quark Stars,

    S. Postnikov, M. Prakash and J. M. Lattimer, “Tidal Love Numbers of Neutron and Self-Bound Quark Stars,” Phys. Rev. D82(2010), 024016

  27. [35]

    S., & Campolattaro, A

    Thorne, K. S., & Campolattaro, A. 1967, ApJ, 149, 591

  28. [36]

    Campolattaro, A., & Thorne, K. S. 1970, ApJ, 159, 847

  29. [37]

    Lindblom and S

    L. Lindblom and S. L. Detweiler, Astrophys. J. Suppl.53, 73 (1983)

  30. [38]

    S. L. Detweiler and L. Lindblom, Astrophys. J.292, 12 (1985)

  31. [39]

    Regge and J

    T. Regge and J. A. Wheeler, Phys. Rev.108, 1063 (1957)

  32. [40]

    Predictions on observing hot holographic quark stars with gravitational waves,

    L. F. Chen, H. Y. Yuan, M. H. Zhou, K. Lu, J. Y. Wu and K. Zhang, “Predictions on observing hot holographic quark stars with gravitational waves,” Phys. Rev. D112(2025) no.12, 123020

  33. [41]

    Hot Holographic 2-Flavor Quark Star,

    L. F. Chen, J. Y. Wu, H. Feng, T. S. Chen and K. Zhang, “Hot Holographic 2-Flavor Quark Star,” Universe11(2025) no.7, 199

  34. [42]

    E. D. Fackerell, Astrophysical Journal, vol.166: 197-206 (1971). – 13 –

Pith tools

Reviewed August 3, 2026 · model on record in the stance chip above.