REVIEW 2 major objections 5 minor 90 references
Four exotic hadrons unified under one scattering framework
Reviewed by Pith at T0; open to challenge. T0 means a machine referee read the full paper against a public rubric. the ladder, T0–T4 →
T0 review · glm-5.2
2026-07-10 01:09 UTC pith:ZWQDZG3X
load-bearing objection The G(3900) claim is the weak link — the cutoff is chosen without an experimental anchor and the resulting pole doesn't match the data. the 2 major comments →
Study of exotic hadron states in the DD^(*) system via the complex momentum representation and Green's function method
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
The CMR combined with the Green's function method provides a single, parameter-stable framework that unifies the description of bound states, resonances, and continuum scattering for the DD* system, allowing X(3872), T_cc^+, and Z_c(3900) to be identified as S-D coupled bound states and G(3900) as a P-wave resonant state, with scattering observables decomposed into resonant and background components.
What carries the argument
The central mechanism is the complex momentum representation (CMR), which deforms the momentum integration contour into the complex plane so that bound-state poles, resonance poles, and continuum states all appear as discrete eigenvalues of a single Hamiltonian matrix. A projection operator method decomposes the momentum-space one-boson-exchange potential into partial waves for systems with coupled spin channels. The Green's function constructed from these complex eigenvalues yields the continuum level density, whose integral gives the scattering phase shift and whose decomposition separates the pure resonance contribution from the continuum background. A monopole form factor with cutoff Λ ~
Load-bearing premise
The binding energies of the three bound states are reproduced by fitting the cutoff parameter of a monopole form factor individually for each state, so the claim of a 'consistent' molecular description rests on the physical validity of a phenomenological one-boson-exchange potential with state-dependent cutoffs rather than a derivation from first principles.
What would settle it
If the scattering phase shifts or cross sections predicted by the CMR Green's function method for the DD* system disagree with future experimental measurements of D D* scattering observables, or if the G(3900) resonance parameters extracted from the pole position fail to match independent amplitude analyses, the unified molecular interpretation would be undermined.
If this is right
- If the CMR framework is valid, scattering phase shifts and cross sections for other exotic hadron candidates near thresholds can be extracted without separate bound-state and scattering calculations.
- The decomposition of phase shifts into resonant and background components could be applied to distinguish genuine resonant poles from threshold cusps in controversial exotic states.
- The finding that P-wave resonances are less sensitive to short-range contact terms than S-wave bound states suggests that P-wave exotic hadron predictions may be more robust against model uncertainties in the short-range potential.
- The method can be extended to other two-hadron systems with coupled spin channels, such as hidden-charm pentaquark candidates or doubly-heavy baryon-meson systems.
Where Pith is reading between the lines
- The fact that different cutoff values are needed for different bound states (0.83 GeV for X(3872) vs 1.0 GeV for Z_c(3900) with contact terms) may indicate that a single universal short-range interaction cannot describe all DD* molecular states simultaneously, which could challenge the 'consistent explanation' claim if one demands a single cutoff.
- The near-threshold narrowing of the G(3900) resonance as the cutoff increases suggests that experimental width measurements could constrain the form-factor cutoff and thereby the spatial extent of the DD* molecular system.
- Extending the CMR framework to coupled-channel problems (e.g., including D*D*, J/psi pi, or eta_c pi channels) would test whether the single-channel molecular interpretation survives when additional decay channels compete.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. This manuscript applies the complex momentum representation (CMR) combined with the Green's function method to the $DD^*$ system within a one-boson-exchange (OBE) framework. The authors employ a projection operator method to construct momentum-space partial-wave potentials, solve the Schrödinger equation directly in momentum space, and extract continuum level densities, scattering phase shifts, and cross sections. They interpret $X(3872)$, $T_{cc}^+$, and $Z_c(3900)$ as $S$–$D$ coupled bound states and $G(3900)$ as a $P$-wave resonance. The methodological framework is clearly presented, and the bound-state results are validated against the complex scaling method (Ref. [60]).
Significance. The integration of CMR with the Green's function method to extract decomposed scattering observables (phase shifts, cross sections) in hadronic physics is a useful technical contribution. The projection operator approach for handling complex spin structures in momentum space is a practical advance over partial-wave expansions requiring Fourier transformation. The systematic comparison of results with and without the short-range contact term $delta$ provides useful phenomenological insight into the sensitivity of $S$-wave bound states versus $P$-wave resonances to short-range physics.
major comments (2)
- §IV, discussion of $G(3900)$: The cutoff parameter for the $G(3900)$ resonance is set to $Lambda = 0.9205$ GeV (with $delta$) or $1.0082$ GeV (without $delta$), chosen to reproduce a resonance energy of $4.25$ MeV above threshold. However, no comparison to the experimentally observed $G(3900)$ properties is provided. The experimental state reported by BaBar and BESIII has a mass near $3900$ MeV (roughly $20$–$30$ MeV above the $Dbar{D}^*$ threshold) and a width of order $100$ MeV or more, whereas the calculated pole sits at $approx 4.25$ MeV above threshold with a width of $sim 37.7$ MeV. The claim that $G(3900)$ 'can be interpreted as a $P$-wave resonant state' is weakened by the absence of any quantitative comparison to experimental data or justification for the chosen $Lambda$. The authors should either (a) state clearly what experimental observables they are targeting and demonstrate
- §IV, Fig. 3 and surrounding text: The pole trajectory of $G(3900)$ is shown as a function of $Lambda$, but the physical criterion for selecting the specific $Lambda$ value used in the scattering calculations is not stated beyond reproducing a chosen resonance energy. Since the pole position varies significantly with $Lambda$ (from $(-7.73, -21.14)$ to $(1.80, -0.49)$ MeV), the physical content of the result depends entirely on this choice. The authors should clarify whether there exists a first-principles or phenomenological criterion for fixing $Lambda$ for resonances (as opposed to fitting to known binding energies for bound states), or acknowledge that the resonance prediction is exploratory rather than definitive.
minor comments (5)
- Table II caption: the cutoff parameters are listed in units of GeV, but the text immediately below states '0.8272, 0.749 and 0.9998 MeV' — these should be GeV, not MeV.
- Fig. 1: the axis labels and legend are rendered as garbled character sequences (e.g., '/s48/s46/s48...'). This appears to be a font or encoding issue that should be fixed for readability.
- §II, Eq. (7): the notation $V_D$ and $V_C$ for direct and cross diagrams is introduced but the superscript $C$ is also used for charge conjugation in §II. Clarifying the notation would avoid confusion.
- §IV: the statement 'the cutoff parameters without the contact term $delta$ are all around 1.0 GeV with smaller variations, which appears better suited to describe hadronic molecular states' is a qualitative judgment. The authors should either provide a quantitative criterion for what constitutes 'better suited' or soften the language.
- References [32]–[35] and [40]–[41] discuss $Z_c(3900)$ and $G(3900)$ interpretations but are cited without detailed comparison to the present results. A brief discussion of how the present findings relate to these prior works would strengthen the paper.
Circularity Check
No significant circularity: the paper is a phenomenological model with fitted parameters, not a circular derivation.
full rationale
The paper applies the complex momentum representation (CMR) combined with the Green's function method to the DD* system using an OBE potential model. The bound-state energies of X(3872), T_cc, and Z_c(3900) are not predicted from first principles; instead, the cutoff parameter Λ is fitted to reproduce known experimental binding energies (Table II). This is standard phenomenological practice — fitting a model parameter to data — and the paper is transparent about this. The G(3900) resonance is then studied using the same framework, with a cutoff chosen to produce a resonance near threshold. While the reader's concern about parameter-fitting is valid as a matter of model-dependence and predictive power, it does not constitute circularity in the sense of a derivation that reduces to its own inputs by construction. The scattering phase shifts and cross sections are derived from the CLD via the Krein-Birman formula (Eqs. 24-25), which is a genuine mathematical relationship, not a tautology. The CLD itself is computed from the discretized complex eigenvalues of the Hamiltonian (Eq. 26), which are obtained by diagonalizing the momentum-space Schrödinger equation with the OBE potential. No step in this chain is self-definitional or reduces to a fit being renamed as a prediction. The paper cites prior work by some of the same authors (Ref. [67]) for the extension of CMR to hadronic physics, but this is a methodological reference, not a load-bearing self-citation that defines the result. The central mathematical framework (CMR + Green's function → CLD → phase shifts) is self-contained and independently verifiable. The phenomenological fitting of Λ to known masses is a model calibration, not a circular argument.
Axiom & Free-Parameter Ledger
free parameters (5)
- Cutoff parameter Λ for X(3872) with contact term =
0.8272 GeV
- Cutoff parameter Λ for T_cc(3875) with contact term =
0.749 GeV
- Cutoff parameter Λ for Z_c(3900) with contact term =
0.9998 GeV
- Cutoff parameter Λ for G(3900) with contact term =
0.9205 GeV
- Coupling constants (g, gV, β, λ, gs, fπ) =
See Table I
axioms (3)
- domain assumption Heavy Meson Chiral Perturbation Theory (HMχPT) and the One-Boson-Exchange (OBE) model provide an adequate effective description of the DD* interaction.
- domain assumption The monopole form factor F(q; m) = (Λ² - m²)/(q² + Λ²) correctly regularizes the short-range behavior of the potential.
- standard math The complex momentum representation (CMR) contour can be deformed to expose resonance poles without altering the physical scattering observables.
Cite this review
Pith. "Pith review of Study of exotic hadron states in the $DD^{*}$ system via the complex momentum representation and Green's function method." pith.science (2026). https://pith.science/paper/ZWQDZG3X
@misc{pith2026260708040,
author = {Pith},
title = {Pith review of: Study of exotic hadron states in the $DD^*$ system via the complex momentum representation and Green's function method},
year = {2026},
howpublished = {\url{https://pith.science/paper/ZWQDZG3X}},
note = {Machine review of arXiv:2607.08040}
}
read the original abstract
In this paper, we propose a novel approach to investigate exotic hadronic states. For the $DD^{*}$ system, we employ the projection operator method to derive the momentum-space interaction potential. Subsequently, the complex momentum representation (CMR) method is adopted to realize a unified description of bound states, resonant states, and the continuum. By combining the Green's function and the CMR, the scattering phase shifts and cross sections are determined. This integrated approach provides a comprehensive framework for analyzing the scattering dynamics of the $DD^{*}$ system. In the hadronic molecular state framework, the $X(3872)$, $T_{cc}^+$, and $Z_c(3900)$ states can be consistently explained as bound states, while the $G(3900)$ can be interpreted as a $P$-wave resonant state. The decomposition of the scattering phase shifts and cross sections facilitates understanding the roles of resonant and continuum spectrum.
Figures
Reference graph
Works this paper leans on
-
[1]
1940 MeV , respectively. By comparison, the cutoff parame- ters without the contact term δare all around 1.0 GeV with smaller variations, which appears better suited to describ e hadronic molecular states. To further investigate the role of the contact term δ, we compare the momentum-space density distributions of X(3872), Tcc(3875), and Zc(3900) with and...
work page 1940
-
[2]
Gell-Mann, Physics Letters, 8, 3, 214-215 (1964)
M. Gell-Mann, Physics Letters, 8, 3, 214-215 (1964)
work page 1964
-
[3]
S. K. Choi et al. [Belle], Phys. Rev. Lett. 91, 262001 (2003)
work page 2003
- [4]
-
[5]
V . M. Abazov et al. [D0], Phys. Rev. Lett. 93, 162002 (2004)
work page 2004
- [6]
-
[7]
H. Xu, B. Wang, Z. W. Liu and X. Liu, Phys. Rev. D 99, 014027 (2019) [erratum: Phys. Rev. D 104, 119903 (2021)]
work page 2019
- [8]
- [9]
-
[10]
H. Ren, F. Wu and R. Zhu, Adv. High Energy Phys. 2022, 9103031 (2022)
work page 2022
- [11]
- [12]
- [13]
-
[14]
P . C. Wallbott, G. Eichmann and C. S. Fischer, Phys. Rev. D 100, 014033 (2019)
work page 2019
-
[15]
R. Zhu, X. Liu, H. Huang and C. F. Qiao, Phys. Lett. B 797, 134869 (2019)
work page 2019
-
[16]
P . G. Ortega, D. R. Entem and F. Fern´ andez, Phys. Lett. B 829, 137083 (2022)
work page 2022
-
[17]
Y . Tan, W. Lu and J. Ping, Eur. Phys. J. Plus 135, 716 (2020)
work page 2020
-
[18]
S. Q. Luo, K. Chen, X. Liu, Y . R. Liu and S. L. Zhu, Eur. Phys . J. C 77, 709 (2017)
work page 2017
-
[19]
F. S. Navarra, M. Nielsen and S. H. Lee, Phys. Lett. B 649, 166-172 (2007)
work page 2007
- [20]
-
[21]
L. Tang, B. D. Wan, K. Maltman and C. F. Qiao, Phys. Rev. D 101, 094032 (2020)
work page 2020
-
[22]
Q. F. L¨ u, D. Y . Chen and Y . B. Dong, Phys. Rev. D102, 034012 (2020)
work page 2020
- [23]
-
[24]
G. J. Wang, X. H. Liu, L. Ma, X. Liu, X. L. Chen, W. Z. Deng and S. L. Zhu, Eur. Phys. J. C 79, 567 (2019)
work page 2019
- [25]
-
[26]
C. E. Thomas and F. E. Close, Phys. Rev. D 78, 034007 (2008)
work page 2008
- [27]
-
[28]
Evidence for X(3872)-->gamma J/psi and the sub-threshold decay X(3872)-->omega J/psi
K. Abe et al. [Belle], [arXiv:hep-ex/0505037 [hep-ex]]
work page internal anchor Pith review Pith/arXiv arXiv
-
[29]
P . del Amo Sanchez et al. [BaBar], Phys. Rev. D 82 (2010), 011101
work page 2010
- [30]
-
[31]
M. Z. Liu, T. W. Wu, M. Pavon V alderrama, J. J. Xie and L. S. Geng, Phys. Rev. D 99, 094018 (2019)
work page 2019
-
[32]
J. B. Cheng, Z. Y . Lin and S. L. Zhu, Phys. Rev. D 106, 016012 (2022)
work page 2022
-
[33]
K. Y u, L. Meng, G. J. Wang, J. J. Wu, and Z. Yang, Phys. Rev. D 110, 114029 (2024)
work page 2024
-
[34]
Y . H. Chen, M. L. Du and F. K. Guo, Sci. China Phys. Mech. Astron. 67, no.9, 291011 (2024) doi:10.1007/s11433- 023-2408-1 [arXiv:2310.15965 [hep-ph]]
work page internal anchor Pith review Pith/arXiv arXiv doi:10.1007/s11433- 2024
-
[35]
H. X. Zhu, L. Meng, Y . Ma, N. Li, W. Chen and S. L. Zhu, Phys. Rev. D 111, 094022 (2025)
work page 2025
-
[36]
S. X. Nakamura, X. H. Li, H. P . Peng, Z. T. Sun and X. R. Zhou, Phys. Rev. D 112, 054027 (2025)
work page 2025
-
[37]
F. K. Guo, C. Hidalgo-Duque, J. Nieves and M. PavonV alde r- rama, Phys. Rev. D 88 (2013), 054007
work page 2013
-
[38]
Q. Wang, C. Hanhart and Q. Zhao, Phys. Rev. Lett. 111, 132003 (2013)
work page 2013
-
[39]
X. X. Chen, Z. M. Ding and J. He, Phys. Rev. D 111, 11 (2025)
work page 2025
- [40]
-
[41]
Z. Y . Lin, J. Z. Wang, J. B. Cheng, L. Meng and S. L. Zhu, Phys. Rev. Lett. 133, 241903 (2024)
work page 2024
-
[42]
Q. Ye, Z. Zhang, M. L. Du, U. G. Meißner, P . Y . Niu and Q. Wang, Phys. Rev. D 112, 016015 (2025)
work page 2025
-
[43]
N. Li, Z. F. Sun, X. Liu and S. L. Zhu, Phys. Rev. D 88 114008, (2013)
work page 2013
-
[44]
L. M. Abreu, Nucl. Phys. B 985, 115994 (2022)
work page 2022
-
[45]
L. M. Abreu, Nucl. Phys. A 940, 1-20 (2015)
work page 2015
- [46]
-
[47]
E. P . Wigner and L. Eisenbud, Phys. Rev. 72 (1947), 29-41
work page 1947
-
[48]
G. M. Hale, R. E. Brown and N. Jarmie, Phys. Rev. Lett. 59 (1987), 763-766
work page 1987
-
[49]
J. Humblet, B. W. Filippone and S. E. Koonin, Phys. Rev. C 44 (1991), 2530-2535
work page 1991
-
[50]
J. R. Taylor, Scattering Theory: The Quantum Theory on N on- relativistic Collisions (John Wiley & Sons, New Y ork, 1972)
work page 1972
-
[51]
A. U. Hazi and H. S. Taylor, Phys. Rev. A 1, 1109 (1970)
work page 1970
-
[52]
V . I. Kukulin, V . M. Krasnoplsky, and J. Horacek, Theory of Resonances: Principles and Applications (Kluwer, Dordrec ht, The Netherlands, 1989)
work page 1989
-
[53]
Y . K. Ho, Phys. Rep. 99, 1 (1983)
work page 1983
- [54]
-
[55]
Z. Y u, M. Song, J. Y . Guo, Y . Zhang and G. Li, Phys. Rev. C 104, 035201 (2021)
work page 2021
-
[56]
G. J. Wang, Q. Meng and M. Oka, Phys. Rev. D 106, 096005 (2022)
work page 2022
-
[57]
Z. P . Wang, F. L. Wang, G. J. Wang and X. Liu, Phys. Rev. D 110, L051501 (2024)
work page 2024
-
[58]
Z. Y . Lin, J. B. Cheng and S. L. Zhu, Phys. Rev. D110, 5 (2024)
work page 2024
-
[59]
Y . K. Chen, L. Meng, Z. Y . Lin and S. L. Zhu, Phys. Rev. D 109, 034006 (2024)
work page 2024
-
[60]
X. H. Mei, Z. Y u, M. Song, J. Y . Guo, G. Li and X. Luo, Chin. Phys. C 47, 033104 (2023)
work page 2023
-
[61]
J. L. Lu, M. Song, P . Wang, J. Y . Guo, G. Li and X. Luo, Eur. Phys. J. C 85, 920 (2025)
work page 2025
- [62]
- [63]
- [64]
-
[65]
C. V . Sukumar, J. Phys. A 12, 1715 (1979)
work page 1979
-
[66]
Y . R. Kwan and F. Tabakin, Phys. Rev. C 18, 932-943 (1978)
work page 1978
-
[67]
N. Li, M. Shi, J. Y . Guo, Z. M. Niu and H. Liang, Phys. Rev. Lett. 117, 062502 (2016)
work page 2016
-
[68]
W. W. He, M. Song, J. Y . Guo, X. Luo and G. Li, Phys. Rev. D 111, 054027 (2025)
work page 2025
-
[69]
L. Meng, V . Baru, E. Epelbaum, A. A. Filin and A. M. Gas- paryan, Phys. Rev. D 109, L071506 (2024)
work page 2024
-
[70]
J. T. Chacko, V . Baru, C. Hanhart and S. L. Krug, Phys. Rev . D 111, 3 (2025)
work page 2025
- [71]
- [72]
- [73]
-
[75]
Y . Nambu and G. Jona-Lasinio, Phys. Rev. 122, 345 (1961); Phys. Rev. 124, 246 (1961)
work page 1961
- [76]
-
[77]
M. B. Wise, Phys. Rev. D 45, R2188 (1992). 13
work page 1992
-
[78]
T. M. Yan, H. Y . Cheng, C. Y . Cheung, G. L. Lin, Y . C. Lin and H. L. Y u, Phys. Rev. D 46, 1148 (1992) [Erratum-ibid. D 55, 5851 (1997)]
work page 1992
-
[79]
R. Casalbuoni, A. Deandrea, N. Di Bartolomeo, R. Gatto, F. Feruglio and G. Nardulli, Phys. Rept. 281, 145 (1997)
work page 1997
-
[80]
A. V . Manohar and M. B. Wise, Camb. Monogr. Part. Phys. Nucl. Phys. Cosmol. 10, 1 (2000)
work page 2000
- [81]
discussion (0)
Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.