REVIEW 3 major objections 4 minor 40 references
$w$-mode oscillation of neutron star in a new relativistic hybrid model
T0 review · 3 major / 4 minor · reviewed 2026-08-05 · deepseek-v4-flash
Pith's one-line read Neutron stars with quarkyonic cores and dark matter would emit gravitational w-modes that are faster and far more damped than ordinary neutron stars.
desk verdict The paper computes plausible w-mode frequencies for a DM-admixed quarkyonic EOS but mislabels them as axial when the formalism is polar, so the central claim needs correction before the numbers can be used. 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 calculation couples the four relativistic pulsation variables (H1, K, W, X) inside the star to the Zerilli equation—the wave equation for even-parity perturbations of the exterior metric—then maps the exterior problem through a phase-amplitude transformation and integrates along a straight line in the complex plane. W-modes are located as complex frequencies at which the outgoing-to-incoming amplitude ratio diverges, enforcing pure outgoing radiation at infinity. The paper labels these as axial modes, although this variable set is the standard one for polar perturbations.
What would settle it
Recompute the l=2 quasinormal-mode frequencies for the same two equations of state using the axial Regge-Wheeler equation, the standard odd-parity counterpart of Zerilli. If the quoted w1–w5 frequencies are reproduced only by the Zerilli/polar calculation and not by the Regge-Wheeler calculation, the paper's axial identification is falsified while the polar spectrum stands. Observationally, a detected neutron-star ringdown whose oscillation frequency and damping time match the table, and whose parity is identified from the gravitational-wave polarization, would settle which mode is present.
Extended reading notes
Core claim
For a non-rotating, canonical-mass neutron star with l=2 perturbations, the paper computes complex quasinormal frequencies of gravitational w-modes using an equation of state built from a relativistic mean-field baryonic parametrization, a quarkyonic crossover transition at n_t=0.3 fm^-3 with confinement scale Λ_cs=800 MeV, and neutralino dark matter with Fermi momentum 0.03 GeV. The exterior is handled with the complex-coordinate phase-amplitude method, and w-modes are identified as singularities of the outgoing/incoming amplitude ratio. The computation yields a w-mode spectrum whose real parts are nearly uniformly spaced (spacing ~0.30 in units of M) and whose imaginary parts are comparabl
Load-bearing premise
The load-bearing premise is that the computed oscillations are axial w-modes; the equations used in the paper are the standard ones for polar oscillations, so if the parity label is mistaken, the frequencies remain valid but describe the other parity class.
Editorial extensions
If this is right
- A gravitational-wave detection of the w-mode ringdown from a neutron star could distinguish a DM-admixed quarkyonic equation of state from a simple polytropic one using only the complex frequency (oscillation plus damping).
- The low quality factors of the hybrid model mean its w-modes decay after roughly one to two cycles, so search strategies should target short, broadband bursts rather than long-lived tones.
- The nearly uniform spacing of the real parts gives a comb-like pattern that could be used as a matched-filter template for higher overtones.
- Because the imaginary part changes more strongly with composition than the real part, accurate damping-time measurements, not just frequencies, carry the equation-of-state information.
Reading between the lines
- If the axial label is wrong, the table is a polar w-mode spectrum; a separate Regge-Wheeler calculation is needed before treating these numbers as axial-mode predictions.
- A clean discriminant experiment would recompute the same two equations of state with the axial Regge-Wheeler equation (the odd-parity counterpart of Zerilli) and compare; a mismatch with the table would confirm the parity issue, while a match would show the two parity sectors happen to give the same frequencies.
- Part of the frequency shift between the two equations of state may track global compactness rather than microscopic composition; plotting Re(ωM) and Im(ωM) against compactness for a sequence of equations of state would isolate the composition dependence the paper attributes to quarkyonic matter and dark matter.
- The more-than-230% increase in damping of the fundamental mode is the most distinctive single observable signature; any future ringdown measurement with even modest sensitivity could target that number as a dark-matter test.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper computes complex gravitational-wave 'w-mode' frequencies for non-rotating neutron stars built from a dark-matter-admixed quarkyonic equation of state, using the IOPB-I relativistic mean-field parametrization, and compares the results with a simple polytropic baseline. The oscillation calculation follows a standard scheme: four perturbation functions (H1, K, W, X) inside the star, the Zerilli equation outside, and the complex-coordinate phase-amplitude method to find quasinormal-mode frequencies. Five l=2 modes are reported; the DM-admixed quarkyonic model shows systematically larger real and imaginary parts and lower quality factors than the polytropic model. The paper interprets these as axial w-modes and argues that they can probe exotic composition in neutron stars.
Significance. If the frequencies are correct and correctly interpreted, the qualitative result that the w-mode spectrum shifts with EOS stiffness and dark-matter admixture would be a useful contribution to gravitational-wave asteroseismology. The use of an established numerical scheme and the comparison against a baseline polytrope are strengths, and the w-mode calculation is largely independent of the EOS construction. However, the paper's central claim is undermined by the axial/polar mismatch: the formalism is unambiguously polar, so the presented spectrum cannot be identified as axial w-modes. This is not a cosmetic issue, because axial and polar w-modes have different equations of motion and different spectra. The manuscript therefore needs substantial correction before its conclusions can be accepted.
major comments (3)
- [§2, Eq. (1); Table 1] The formalism is polar, not axial. The interior perturbation functions H1, K, W, X (cited to Detweiler & Lindblom [31]) are the standard even-parity variables, and Eq. (1) is the Zerilli equation, the even-parity exterior wave equation. Axial (odd-parity) perturbations of a non-rotating perfect-fluid star obey the Regge-Wheeler equation and do not involve fluid variables W and X. Therefore the frequencies in Table 1 and Figure 1 are polar w-modes, not the axial w-modes claimed in the abstract, introduction, and conclusions. The concluding statement that 'axial perturbations governing w-modes depend on the internal density and pressure distributions' confuses the two parities. The authors must either redo the calculation with the axial formalism and matching boundary conditions, or explicitly re-frame the entire paper as a study of polar w-modes and adjust all claims accordingly.
- [§3, Table 1 and Fig. 1] No numerical validation or uncertainty estimates are provided. The central quantitative claims—for example, that Im(ωM) increases by more than 230% for w1, or that Q and R cleanly separate the two EOS models—depend entirely on the accuracy of the complex-coordinate integration and root finding. The manuscript should include convergence tests with respect to grid resolution, the matching radius, the integration path angle θ, and a comparison with known polytropic w-mode frequencies from the literature. Without any such checks the tabulated values are not reproducible and the quantitative comparison is not supported.
- [§3, Table 1] The stellar and EOS inputs are incompletely specified. The polytropic constant K (and the index, if P = Kε^2 is meant to be a γ=2 polytrope) are not given. The masses and radii of the two comparison stars are not stated, even though the frequencies are quoted in units of the stellar mass M. The phrase 'canonical star' is used but never defined quantitatively. Without these values, the reader cannot reproduce Table 1 or determine whether the comparison is at fixed mass, which is essential for interpreting the ωM scaling and the claimed differences.
minor comments (4)
- [§2, Eq. (10)] The quantities Z_S and Z'_S appearing in Eq. (10) are not defined. Presumably they are the Zerilli function and its derivative evaluated at the stellar surface; please define them explicitly.
- [Abstract; §4] The abstract states that w-modes 'emerge from the coupling between the star's fluid component and the gravitational field.' For axial w-modes this is not the standard picture; if the paper is revised to polar w-modes, the statement should be reworded to describe the coupling appropriate to even-parity fluid perturbations.
- [§3, Fig. 2] The text mentions that higher overtones w6 and w7 survive for the polytrope but are suppressed for the DM-admixed case, yet no w6 or w7 frequencies are shown. Either provide these values or remove the claim.
- [General / References] Reference [38] is a 'manuscript under preparation' and should not be invoked to support scientific conclusions. Also, Figure axis labels contain typographical issues (e.g., 'MeVVfm 3') and should be corrected.
Circularity Check
No circular reduction; minor self-citations are not load-bearing. The axial/polar labeling issue is a correctness concern, not a circularity.
full rationale
The derivation chain is explicit: the EOS is fixed first (IOPB-I RMF hadronic sector fitted to nuclear data; quarkyonic parameters nt=0.3 fm^-3 and Lambda_cs=800 MeV; DM Fermi momentum k_f^DM=0.03 GeV), the TOV background is computed, and the w-mode frequencies are then obtained as singularities of the exterior amplitude ratio, Eq. (10), after integrating the interior perturbation system in H1, K, W, X with the exterior Zerilli equation. No parameter in this chain is fitted to the tabulated w-mode frequencies, and the modes are not defined in terms of the EOS parameters; they are genuine outputs of a boundary-value problem. The paper contains self-citations ([4], [35]) for the DM-admixed quarkyonic EOS construction and a predicted maximum mass, but those inputs are stated in the text and are not the target of the w-mode calculation, so they are not load-bearing in a circular sense. A separate, non-circularity issue is that the equations used (H1,K,W,X and the Zerilli equation) are standard even-parity polar perturbation variables, while the paper labels the modes 'axial' and asserts in the Conclusions that 'axial perturbations governing w-modes depend on the internal density and pressure distributions'; this is a physical/interpretation inconsistency, not a reduction of the prediction to its inputs. Overall: no significant circularity; score 2 only for minor non-load-bearing self-citation.
Assumptions & free parameters
free parameters (4)
- nt (quarkyonic transition density) =
0.3 fm^-3
- Lambda_cs (confinement scale) =
800 MeV
- k_f^DM (DM Fermi momentum) =
0.03 GeV
- Polytropic EOS constant K =
unspecified
assumptions (4)
- standard math General relativity with TOV equations describes the unperturbed star
- domain assumption Quarkyonic matter exists as a crossover state with quasiparticle nucleons and quark core
- domain assumption Fermionic dark matter interacts with nucleons via the Higgs portal
- ad hoc to paper The Zerilli equation is the correct exterior master equation for the computed w-modes
Cite this review
Pith. "Pith review of $w$-mode oscillation of neutron star in a new relativistic hybrid model." pith.science (2026). https://pith.science/paper/QZIJMJNQ
@misc{pith2026250901175,
author = {Pith},
title = {Pith review of: $w$-mode oscillation of neutron star in a new relativistic hybrid model},
year = {2026},
howpublished = {\url{https://pith.science/paper/QZIJMJNQ}},
note = {Machine review of arXiv:2509.01175}
}
abstract
We investigate how the pulsation frequencies of axial gravitational-wave modes ($w$-modes) in a non-rotating neutron star depend on its composition, particularly when including quarkyonic matter and fermionic dark matter. These modes emerge from the coupling between the star's fluid component and the gravitational field of general relativity, which are highly damped and characterized by complex frequencies with comparable real and imaginary parts. Using a relativistic mean field formalism for the nucleonic component, we modeled the neutron star's interior, while the exterior is analyzed through the complex-coordinate method to determine the $w$-modes. Our study employs a realistic equation of state, based on different physical assumptions and covering a broad area of observational constraints, starting from finite nuclei to nuclear matter with extreme conditions. The numerical findings demonstrate that axial $w$-modes provide valuable insights into the properties of neutron star matter, highlighting their significance in probing the star's internal structure.
Figures
Reference graph
Works this paper leans on
-
[31]
S. Detweiler, L. Lindblom, On the nonradial pulsations of general rela- tivistic stellar models, Astrophys. J. 292 (1985) 12–15. doi:10.1086/ 163127
work page 1985
-
[1]
J. M. Lattimer, M. Prakash, The physics of neutron stars, Science 304 (5670) (2004) 536–542. doi:10.1126/science.1090720. URL https://science.sciencemag.org/content/304/5670/ 536
-
[2]
Burrows, Supernova explosions in the universe, Nature 403 (6771) (2000) 727–733
A. Burrows, Supernova explosions in the universe, Nature 403 (6771) (2000) 727–733. doi:10.1038/35001501. URL https://doi.org/10.1038/35001501
doi:10.1038/35001501 2000
-
[3]
T. Zhao, J. M. Lattimer, Universal relations for neutron star f - mode and g-mode oscillations, Phys. Rev. D 106 (2022) 123002. doi:10.1103/PhysRevD.106.123002. URL https://link.aps.org/doi/10.1103/PhysRevD.106. 123002
-
[4]
D. Dey, J. A. Pattnaik, H. C. Das, A. Kumar, R. N. Panda, S. K. Patra, Dark matter influence on quarkyonic stars: a relativistic mean field anal- ysis, JCAP 01 (2025) 056. doi:10.1088/1475-7516/2025/01/056
-
[5]
K. D. Kokkotas, B. F. Schutz, W-modes: a new family of normal modes of pulsating relativistic stars, MNRAS 255 (1) (1992) 119–128. doi: 10.1093/mnras/255.1.119
-
[6]
N. Stergioulas, K. D. Kokkotas, I. Hawke, W-Modes in Rotating Rela- tivistic Stars, in: N. Solomos (Ed.), Recent Advances in Astronomy and Astrophysics, V ol. 848 of American Institute of Physics Conference Se- ries, 2006, pp. 730–737. doi:10.1063/1.2348051. 4
-
[7]
N. Andersson, K. D. Kokkotas, Towards gravitational wave astero- seismology, MNRAS 299 (4) (1998) 1059–1068. doi:10.1046/j. 1365-8711.1998.01840.x
arXiv 1998
Show all 40 references
-
[8]
H. Das, A. Kumar, B. Kumar, S. Biswal, S. Patra, Impacts of dark matter on the curvature of the neutron star, JCAP 2021 (01) (2021) 007. doi: 10.1088/1475-7516/2021/01/007. URL https://dx.doi.org/10.1088/1475-7516/2021/01/007
2021 doi
-
[9]
S. K. Patra, M. Centelles, X. Vi ˜nas, M. Del Estal, Surface incompress- ibility from semiclassical relativistic mean field calculations, Phys. Rev. C 65 (2002) 044304. doi:10.1103/PhysRevC.65.044304. URL https://link.aps.org/doi/10.1103/PhysRevC.65. 044304
2002 doi
-
[10]
M ¨uller, B
H. M ¨uller, B. D. Serot, Relativistic mean-field theory and the high- density nuclear equation of state, Nucl. Phys. A 606 (3) (1996) 508–537. doi:https://doi.org/10.1016/0375-9474(96)00187-X . URL https://www.sciencedirect.com/science/article/pii/ 037594749600187X
1996 doi
-
[11]
Wang, Asymmetric nuclear matter at finite temperature and density, Phys
P. Wang, Asymmetric nuclear matter at finite temperature and density, Phys. Rev. C 61 (2000) 054904. doi:10.1103/PhysRevC.61.054904. URL https://link.aps.org/doi/10.1103/PhysRevC.61. 054904
2000 doi
-
[12]
Kumar, H
A. Kumar, H. C. Das, S. K. Biswal, B. Kumar, S. K. Patra, Warm dense matter and cooling of supernovae remnants, Euro. Phys. J. C 80 (8) (2020) 775. doi:10.1140/Euro.Phys.J.C/s10052-020-8353-4 . URL https://doi.org/10.1140/Euro.Phys.J.C/ s10052-020-8353-4
2020 doi
-
[13]
L. D. Miller, A. E. S. Green, Relativistic self-consistent meson field the- ory of spherical nuclei, Phys. Rev. C 5 (1972) 241–252. doi:10.1103/ PhysRevC.5.241. URL https://link.aps.org/doi/10.1103/PhysRevC.5.241
1972 doi
-
[14]
R. J. Furnstahl, C. E. Price, G. E. Walker, Systematics of light deformed nuclei in relativistic mean-field models, Phys. Rev. C 36 (1987) 2590–
1987
-
[15]
Reinhard, The nonlinearity of the scalar field in a relativistic mean- field theory of the nucleus, Zeitschrift f¨ur Physik A Atomic Nuclei 329 (3) (1988) 257–266
P.-G. Reinhard, The nonlinearity of the scalar field in a relativistic mean- field theory of the nucleus, Zeitschrift f¨ur Physik A Atomic Nuclei 329 (3) (1988) 257–266. doi:10.1007/BF01290231. URL https://doi.org/10.1007/BF01290231
1988 doi
-
[16]
Furnstahl, B
R. Furnstahl, B. D. Serot, H.-B. Tang, A chiral effective lagrangian for nu- clei, Nucl. Phys. A 615 (4) (1997) 441–482. doi:https://doi.org/ 10.1016/S0375-9474(96)00472-1 . URL https://www.sciencedirect.com/science/article/pii/ S0375947496004721
1997 doi
-
[17]
B. P. Abbott, R. Abbott, T. D. Abbott, et al., Gw170817: Observation of gravitational waves from a binary neutron star inspiral, Phys. Rev. Lett. 119 (2017) 161101. doi:10.1103/PhysRevLett.119.161101. URL https://link.aps.org/doi/10.1103/PhysRevLett.119. 161101
2017 doi
-
[18]
S. De, D. Finstad, J. M. Lattimer, D. A. Brown, E. Berger, C. M. Biwer, Tidal deformabilities and radii of neutron stars from the observation of gw170817, Phys. Rev. Lett. 121 (2018) 091102. doi:10.1103/PhysRevLett.121.091102. URL https://link.aps.org/doi/10.1103/PhysRevLett.1...
2018 doi
-
[19]
B. P. Abbott, R. Abbott, T. D. Abbott, et al., Gw170817: Measurements of neutron star radii and equation of state, Phys. Rev. Lett. 121 (2018) 161101. doi:10.1103/PhysRevLett.121.161101. URL https://link.aps.org/doi/10.1103/PhysRevLett.121. 161101
2018 doi
-
[20]
C. D. Capano, I. Tews, S. M. Brown, B. Margalit, S. De, S. Kumar, D. A. Brown, B. Krishnan, S. Reddy, Stringent constraints on neutron-star radii from multimessenger observations and nuclear theory, Nature Astronomy 4 (6) (2020) 625–632. doi:10.1038/s41550-020-1014-6 . URL htt...
2020 doi
-
[21]
T. E. Riley, A. L. Watts, S. Bogdanov, et al., A NICER View of PSR J0030+0451: Millisecond Pulsar Parameter Estimation, APJL 887 (1) (2019) L21. doi:10.3847/2041-8213/ab481c
2019 doi
-
[22]
M. C. Miller, F. K. Lamb, A. J. Dittmann, other, Psr j0030 +0451 mass and radius from nicer data and implications for the properties of neutron star matter, The Astrophys. J. Letters 887 (1) (2019) L24.doi:10.3847/ 2041-8213/ab50c5. URL https://dx.doi.org/10.3847/2041-8213/ab50c5
2019 doi
-
[23]
¨Ozel, P
F. ¨Ozel, P. Freire, Masses, radii, and the equation of state of neutron stars, Annu. Rev. Astron. Astrophys. 54 (V olume 54, 2016) (2016) 401–440. doi:https://doi.org/10.1146/ annurev-astro-081915-023322 . URL https://www.annualreviews.org/content/journals/10. 1146/annurev-as...
2016
-
[24]
J. M. Lattimer, The nuclear equation of state and neutron star masses, Annu. Rev. Nucl. Part. Sci. 62 (V olume 62, 2012) (2012) 485–515. doi:https://doi.org/10.1146/annurev-nucl-102711-095018 . URL https://www.annualreviews.org/content/journals/10. 1146/annurev-nucl-102711-095018
2012 doi
-
[25]
McLerran, S
L. McLerran, S. Reddy, Quarkyonic matter and neutron stars, Phys. Rev. Lett. 122 (2019) 122701. doi:10.1103/PhysRevLett.122.122701. URL https://link.aps.org/doi/10.1103/PhysRevLett.122. 122701
2019 doi
-
[26]
T. Zhao, J. M. Lattimer, Quarkyonic matter equation of state in beta-equilibrium, Phys. Rev. D 102 (2020) 023021. doi:10.1103/PhysRevD.102.023021. URL https://link.aps.org/doi/10.1103/PhysRevD.102. 023021
2020 doi
-
[27]
Panotopoulos, I
G. Panotopoulos, I. Lopes, Dark matter e ffect on realistic equa- tion of state in neutron stars, Phys. Rev. D 96 (2017) 083004. doi:10.1103/PhysRevD.96.083004. URL https://link.aps.org/doi/10.1103/PhysRevD.96. 083004
2017 doi
-
[28]
Quddus, G
A. Quddus, G. Panotopoulos, B. Kumar, S. Ahmad, S. K. Patra, Gw170817 constraints on the properties of a neutron star in the pres- ence of wimp dark matter, Jour. Phys. G 47 (9) (2020) 095202. doi: 10.1088/1361-6471/ab9d36. URL https://dx.doi.org/10.1088/1361-6471/ab9d36
2020 doi
-
[29]
R. C. Tolman, Static solutions of einstein’s field equations for spheres of fluid, Phys. Rev. 55 (1939) 364–373. doi:10.1103/PhysRev.55.364. URL https://link.aps.org/doi/10.1103/PhysRev.55.364
1939 doi
-
[30]
J. R. Oppenheimer, G. M. V olkoff, On massive neutron cores, Phys. Rev. 55 (1939) 374–381. doi:10.1103/PhysRev.55.374. URL https://link.aps.org/doi/10.1103/PhysRev.55.374
1939 doi
-
[32]
E. D. Fackerell, Solutions of zerilli’s equation for even-parity gravi- tational perturbations, Astrophys. J. 166 (1971) 197. doi:10.1086/ 150949
1971
-
[33]
Andersson, K
N. Andersson, K. D. Kokkotas, B. F. Schutz, A new numerical approach to the oscillation modes of relativistic stars, MNRAS 274 (4) (1995) 1039–1048. doi:10.1093/mnras/274.4.1039
1995 doi
-
[34]
Kumar, S
B. Kumar, S. K. Patra, B. K. Agrawal, New relativistic e ffective interac- tion for finite nuclei, infinite nuclear matter, and neutron stars, Phys. Rev. C 97 (2018) 045806. doi:10.1103/PhysRevC.97.045806. URL https://link.aps.org/doi/10.1103/PhysRevC.97. 045806
2018 doi
-
[35]
D. Dey, J. A. Pattnaik, M. Bhuyan, R. Panda, S. Patra, f-mode oscillations of dark matter admixed quarkyonic neutron star, JCAP 2025 (08) (2025)
2025
-
[36]
K. D. Kokkotas, B. G. Schmidt, Quasi-normal modes of stars and black holes, Living Reviews in Relativity 2 (2) (1999) 2. doi:10.12942/ lrr-1999-2 . URL https://doi.org/10.12942/lrr-1999-2
1999 doi
-
[37]
URL https://dx.doi.org/10.1088/1475-7516/2025/08/003
doi:10.1088/1475-7516/2025/08/003. URL https://dx.doi.org/10.1088/1475-7516/2025/08/003
2025 doi
-
[38]
D. Dey, S. K. Patra, manuscript under preparation (2025). 5
2025
-
[39]
Berti, V
E. Berti, V . Cardoso, C. M. Will, Gravitational-wave spectroscopy of mas- sive black holes with the space interferometer lisa, Physical Review D 73 (2006) 064030. doi:10.1103/PhysRevD.73.064030. URL https://doi.org/10.1103/PhysRevD.73.064030
2006 doi
-
[2600]
URL https://link.aps.org/doi/10.1103/PhysRevC.36.2590
doi:10.1103/PhysRevC.36.2590. URL https://link.aps.org/doi/10.1103/PhysRevC.36.2590
Reviewed August 5, 2026 · model on record in the stance chip above.
Discussion (0). Continue with ORCID to comment.