REVIEW 4 major objections 5 minor 44 references
The Study of Pole Trajectory within a bare state in the coupled channel model
T0 review · 4 major / 5 minor · reviewed 2026-08-07 · deepseek-v4-flash
Pith's one-line read A bare state guarantees a nearby physical pole in this model.
desk verdict Useful toy-model map of pole trajectories and compositeness in one-bare-state HEFT, but the 'always' claim outruns the regulator-dependent evidence. 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 load-bearing object is the pole trajectory: the path traced in the complex energy plane by T-matrix poles as the coupling constants $v$ (two-body) and $g$ (bare-to-channel) are varied. The model uses separable interactions, of the form $v f(k)f(k')$, so the pole condition reduces to a one-dimensional algebraic equation $\det\{1 - v\int dq\, q^2 f(q)^2/(E-\omega(q))\}=0$, with relativistic channel energy $\omega(k)=\sqrt{m_M^2+k^2}+\sqrt{m_N^2+k^2}$. The form factor $f$ carries powers of the regulator $u(k)=(1+k^2/\Lambda^2)^{-2}$, and that power determines how many poles the equation has. For the case with a bare state, the full amplitude is built from the dressed vertex and the one-loop self-energy, and full poles solve $\det\{\delta_{BB'}(E-m_B)-\overline{\Sigma}_{BB'}(E)\}=0$. The same self-energy derivative defines the bare-state probability $1/Z$ of a bound state.
What would settle it
Repeat the calculation with regulator $u(k)=\exp(-k^2/\Lambda^2)$ or a different power $n$; if the trajectory starting at the bare-state mass ceases to produce a physical pole near that mass, or if $1/Z$ no longer vanishes for shallow S-wave bound states, the claims are regulator artifacts.
Extended reading notes
Core claim
The paper's central claim is that the presence of a bare state in a one-channel two-body scattering model exerts a systematic, predictable influence on the physical poles: if the bare state exists, a physical state will always emerge in its vicinity. The bare state acts as an energy-dependent two-body interaction that is attractive below the bare mass and repulsive above it; the relative position of the bare mass to the threshold therefore decides whether the adjacent pole is a bound state or a resonance. In addition, the authors establish that the smooth regulator $u(k)=(1+k^2/\Lambda^2)^{-2}$ generates one extra pole per power of the denominator, that only near-threshold poles are robust, and that for S-wave shallow bound states the bare-state component $1/Z$ tends to zero at threshold, making the compositeness approach unity.
Load-bearing premise
The whole pole-count and near-threshold compositeness pattern rests on the chosen separable potential and the smooth regulator $u(k)=(1+k^2/\Lambda^2)^{-2}$; a different regulator can change the number of physical-looking poles and the behavior of $1/Z$ at threshold.
Editorial extensions
If this is right
- Near-threshold S-wave bound states in this model are almost entirely two-body composites: $1/Z$ goes to zero as binding energy goes to zero, so their compositeness is close to 1.
- If the bare state sits below threshold, the two-body attraction creates one bound state near the bare mass and can push another pole above it into a virtual state or resonance; the ordering of bare mass and threshold is a controlling parameter.
- Two-body repulsion can still produce a bound state when a bare state is present, because the bare-state exchange provides the attraction; this suggests searching for hadrons whose molecular constituents repel.
- Poles far from threshold, including some resonances with large widths, are artifacts of the chosen regulator and should be discarded when fitting data.
- Relativistic kinematics allows resonance-like poles with real part below threshold, so experimental analyses should not assume a below-threshold complex pole is unphysical.
Reading between the lines
- The claimed 'always a pole near the bare state' likely generalizes to any model with an energy-dependent separable interaction of the same sign structure, not only this regulator; a direct test would be to repeat the trajectory study with a dipole or exponential form factor.
- The threshold behavior of compositeness may offer a model-independent observable: measurement of a near-threshold S-wave state's binding energy and scattering length constrains its molecular probability, and this model shows the bare-state component is suppressed there, so a measured large bare component would falsify this class of models.
- The same pole-trajectory machinery could be applied to finite-volume spectra, connecting the bare-state pole positions to lattice-QCD energy levels, because the model's Hamiltonian form gives both infinite- and finite-volume amplitudes.
- The form-factor pole counting may explain why fits with different regulators obtain different numbers of resonances from the same data; a comparison of phase-shift fits across regulators would quantify the systematic uncertainty.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper studies a one-channel, one-bare-state Hamiltonian effective field theory (HEFT) with separable potentials, solving the Lippmann-Schwinger equation for T-matrix poles in both non-relativistic and relativistic kinematics. It makes three main claims: (i) the number of T-matrix poles increases with the power n of the regulator u(k) = (1+k^2/Λ^2)^{-n}; (ii) in the absence of a bare state, attractive and repulsive two-body couplings generate pole trajectories for bound, virtual, and resonance states, with relativistic kinematics producing below-threshold resonances; and (iii) when a bare state is included, a physical pole always appears in the vicinity of the bare mass, and for shallow S-wave bound states the bare-state component tends to vanish at threshold unless the two-body potential is repulsive. The paper draws qualitative comparisons to X(3872) and D*_s0(2317).
Significance. If the central claims hold, the paper provides a useful qualitative map of how a bare state reshapes near-threshold pole structure in HEFT, and it offers falsifiable expectations for near-threshold states. The analytic loop integrals for n=1 and n=2 in the non-relativistic case and the direct solution of the coupled-channel equations are valuable, and the discussion of which poles are form-factor artifacts is a useful caution. However, the generality of the 'a physical state always emerges in the vicinity of a bare state' statement and the claimed universal threshold behavior of 1/Z are not established beyond the single smooth regulator used; the paper itself concedes in Section V that the form factor is an assumption. The underlying derivation is sound enough that the issues are fixable, but the conclusions need to be qualified and several technical points need to be clarified.
major comments (4)
- [III, Eqs. (31)-(34)] The paper states that the number of T-matrix poles equals n and that 'it can be proven analytically in the non-relativistic case,' but the text supplies only the n=1 and n=2 examples and no general proof. Since the subsequent exclusion of 'model-dependent' poles relies on this pole-counting statement, either supply the promised proof (for example, by deriving the polynomial degree of the analytically continued loop function) or soften the claim to a conjecture supported by examples. In addition, Eq. (34) contains an apparent typo in the term '16i√μ√(k0^2)μ', which prevents the reader from reproducing the claimed n=2 pole positions.
- [IV.B and VI] The conclusion that 'if a bare state exists, a physical state will always emerge in its vicinity' is drawn from pole trajectories computed for a single regulator u(k) = (1+k^2/Λ^2)^{-2} with Λ = 0.8 GeV and two arbitrarily chosen bare masses. In Section V the authors themselves write that the results 'suffer the uncertainties of the form factor which form actually is an assumption.' Since Section III shows that the form factor changes the number and location of poles, the 'always' claim and the unqualified summary in Section VI need to be restricted to this toy regulator or tested with other regulators or powers n; without that, the claim is a property of the chosen model, not of the coupled-channel framework.
- [V, Eq. (30)] The relation between Z and 1/Z is inconsistent. Equation (29) normalizes the bound state with coefficient 1/Z^{1/2}, so the bare-state probability is 1/Z, but the sentence following Eq. (30) says that the probability of finding the bare component is 'Z = 1 - dΣ/dE'. Section V then plots 1/Z as the bare-state probability. Please correct the definition or the wording; as written, the interpretation of Figs. 11-16 is ambiguous.
- [V, Figs. 11-16] The universal statement that 'for the S-wave bound state ... the compositeness always becomes 1 when it is a shallow bound state' is supported only by selected values of v and g. The threshold derivative of the self-energy depends on the regulator and on the masses, and Figs. 12-13 show that the behavior of Re Σ at threshold changes qualitatively with v. Either prove the threshold limit analytically from Eq. (31) or present a scan over the parameter space. The corresponding P-wave statement that the loop function has no extremum at threshold is likewise obtained for the specific form factor f(k) and needs the same qualification.
minor comments (5)
- [Title] The title contains 'couple d channel' with an unwanted space; please fix.
- [General] There are several typographical errors: 'possibilities' should be 'probabilities', 'Hear' should be 'Here', and 'out of the current model' should be 'outside the current model'.
- [Figures 7-10] The figure captions contain garbled text such as 'H e WBMVF' and '3F &'; please regenerate the captions so that the fonts render correctly.
- [II.A and III] Equation (11) defines the S-wave form factor with a factor of 5 and a factor 1/ω_M(k), while Eq. (32) uses a simpler '2/(1+(k/Λ)^2)^n'. Please clarify whether the illustrative form in Section III is meant to be a different choice or a shorthand, so that the pole-counting discussion can be connected to the numerical calculations in Section IV.
- [IV.A] The captions of Figs. 5 and 6 are missing 'changing with' in 'The pole positions with S-wave interaction strength' and 'The pole positions with P-wave interaction strength'; please reword for clarity.
Circularity Check
No significant circularity: poles are solved from the model equations, and the regulator dependence is explicitly acknowledged as an assumption.
full rationale
The derivation is self-contained: pole positions are obtained by solving the algebraic determinant conditions (14) and (24) with the stated separable-potential and regulator inputs; the compositeness 1/Z is evaluated from the derived relation Z = 1 - dSigma/dE at the solved bound-state energy (Eqs. 28-30), so no fitted parameter is renamed as a prediction. The 'bare state always yields a nearby physical pole' statement follows from the pole equation E - mB - Sigma(E) = 0 starting from the g=0 pole at mB; the paper itself calls this 'obviously' and uses it only as a model property, not as a fit. The phase-shift fits in Section III are used to screen form-factor poles, not to produce the trajectory or compositeness results. The regulator sensitivity is explicitly acknowledged in Section V ('the Sigma(E) would suffer the uncertainties of the form factor which form actually is an assumption'), so the concern about regulator dependence is a robustness/overgeneralization issue, not circularity. Self-citations to earlier HEFT papers provide the regulator convention, but the paper treats the form factor as a toy-model assumption rather than as an externally certified input, so the citations are not load-bearing in the derivation.
Assumptions & free parameters
free parameters (6)
- two-body coupling v =
scanned over ranges, e.g., -0.2 to 0.09 in figures
- bare-state coupling g =
scanned over ranges
- regulator Lambda =
0.8 GeV (1 GeV in Section III examples)
- particle masses mM and mN =
0.2 GeV and 0.8 GeV
- bare mass mB0 =
1.3 GeV or 0.7 GeV
- form-factor power n =
n=2 in Section IV; n=1,2,3 in Section III
assumptions (5)
- standard math The Lippmann-Schwinger equation with the i-epsilon prescription yields the T-matrix poles on the appropriate Riemann sheets.
- domain assumption Interactions are separable potentials with the form factor u(k)=(1+k^2/Lambda^2)^-2.
- domain assumption The relativistic dispersion relation omega(k)=sqrt(m1^2+k^2)+sqrt(m2^2+k^2) holds.
- ad hoc to paper The model is only reliable near threshold; far-away poles are discarded as form-factor artifacts.
- domain assumption The bare state and its coupling in the Hamiltonian represent an elementary particle, and its probability in a bound state is read off from Z.
Cite this review
Pith. "Pith review of The Study of Pole Trajectory within a bare state in the coupled channel model." pith.science (2026). https://pith.science/paper/SUBFV7GB
@misc{pith2026250602526,
author = {Pith},
title = {Pith review of: The Study of Pole Trajectory within a bare state in the coupled channel model},
year = {2026},
howpublished = {\url{https://pith.science/paper/SUBFV7GB}},
note = {Machine review of arXiv:2506.02526}
}
read the original abstract
We investigate two-particle scattering and two-particle scattering with a bare basis state using Hamiltonian Effective Field Theory (HEFT). We analyze the distribution of two-body scattering poles in the momentum and energy planes under relativistic conditions. Compared to the non-relativistic case, there are significant differences in the distribution of bound state poles and resonance poles in the relativistic case, primarily due to the square root term in the relativistic formula. By considering pure two-particle scattering, we examine the relationship between the form factor and the number of poles. Additionally, we clearly elucidate the effects of attractive and repulsive interactions on the bound state poles and resonance poles. More importantly, we extend our model by including a bare state and explore the poles originating from the bare state or coupled channels through the trajectories of pole positions, as well as the compositeness of bound states.
Figures
Figures from the paper (12 more)
Reference graph
Works this paper leans on
-
[1]
The complex E-plane can be divided into two Riemann sheets. The physical sheet (first sheet) is defined by the range of the phase 0 ≤ φE ≤ 2π and the unphysical sheet (second sheet) by 2 π ≤ φE ≤ 4π. On the different Riemann sheet, one can find singular- arXiv:2506.02526v1 [hep-ph] 3 Jun 2025 2 ities of the S-matrix which correspond to bound state, resonance ...
arXiv 2025
-
[2]
While bound state poles [solid squares in Fig. 2a] remain lo- cated on the real axis of the momentum imaginary plane, similar to the non-relativistic scenario, their correspond- ing positions on the energy plane differ significantly, as shown in Fig. 2b. Furthermore, a comparison of Fig. 1c, Fig. 1d, Fig. 2c, and Fig. 2d reveals that although the 7th region...
-
[3]
H. W. Hammer, C. Ji, and D. R. Phillips. Effective field theory description of halo nuclei. J. Phys. G , 44(10):103002, 2017
work page 2017
-
[4]
B. C. Pearce and B. F. Gibson. Observable Effects of Poles and Shadow Poles in Coupled Channel Systems. Phys. Rev. C , 40:902–911, 1989
work page 1989
-
[5]
This can be easily understood because, to satisfy the condition of Eq
Finally, it is worth mentioning that the trajectory of this pole is discontinuous at vαα = 0. This can be easily understood because, to satisfy the condition of Eq. ( 11), even if they are on the same Riemann sheet, as vαα changes from 0 − to 0 +, the corresponding integral transitions from −∞ to + ∞. Consequently, the positions of the poles will not FIG....
-
[6]
It shows that the trajectory of the poles is relatively natural, as the attractive strength increases, the poles gradually shift from the resonance pole to the bound state pole. As the strength further increases, the bound state will move away from the threshold, become a deeper bound state. In this case, we noticed a very strange phenomenon that the reso...
-
[7]
and ( 11), respectively. As shown in Fig. 7, the pole trajectories is shown clearly. We find one pole trajectory always begins with bare state, which is obviously, because the bare state will be a real physi- cal pole once no interaction between the bare state and the coupled channels, i.e., g = 0. Thus, we can see that regardless of whether v is attractiv...
-
[8]
This has good physical correspondence; many resonance states, such as the κ meson and the σ meson, are examples of this case. Meanwhile, when v is repulsive, the trajectory of singu- larities along the dotted line is evidently far from the physical region being discussed, which we have found ac- tually originates from the form factor of the model and can ...
Show all 44 references
-
[9]
We guess that the ρ meson, the K ∗ meson and ∆(1232) baryon, are examples of this case
However, for the attractive v, when the v is not large enough, the pole trajectories are similar as that for repulsive v. We guess that the ρ meson, the K ∗ meson and ∆(1232) baryon, are examples of this case. Only when the attractive in- teraction of v is large enough, the po...
-
[10]
( 6,7), respec- tively
and Eqs. ( 6,7), respec- tively. In order to more clearly distinguish the differences in the effects they bring, we observe by changing the value of g under different values of v. Firstly, we considering the S-wave interactions with a bare state above the threshold. The G and f f...
-
[11]
Suzuki, T
N. Suzuki, T. Sato, and T. S. H. Lee. Extraction of Resonances from Meson-Nucleon Reactions. Phys. Rev. C, 79:025205, 2009
2009
-
[12]
H. W. Hammer, S. K¨ onig, and U. van Kolck. Nuclear effective field theory: status and perspectives. Rev. Mod. Phys., 92(2):025004, 2020
2020
-
[13]
Structure of Near-Threshold s-Wave Res- onances
Tetsuo Hyodo. Structure of Near-Threshold s-Wave Res- onances. Phys. Rev. Lett. , 111:132002, 2013
2013
-
[14]
Doring, C
M. Doring, C. Hanhart, F. Huang, S. Krewald, and U. G. Meissner. Analytic properties of the scattering amplitude and resonances parameters in a meson exchange model. Nucl. Phys. A , 829:170–209, 2009
2009
-
[15]
Meiss- ner
Feng-Kun Guo, Christoph Hanhart, and Ulf-G. Meiss- ner. Interactions between heavy mesons and Goldstone bosons from chiral dynamics. Eur. Phys. J. A , 40:171– 179, 2009
2009
-
[16]
Inverse scattering problem with a bare state
Yan Li and Jia-Jun Wu. Inverse scattering problem with a bare state. Phys. Rev. D , 105(11):116024, 2022
2022
-
[17]
Structure of Λ(1405) and threshold behavior of π Σ scattering
Yoichi Ikeda, Tetsuo Hyodo, Daisuke Jido, Hiroyuki Kamano, Toru Sato, and Koichi Yazaki. Structure of Λ(1405) and threshold behavior of π Σ scattering. Prog. Theor. Phys. , 125:1205–1224, 2011
2011
-
[18]
Virtual states in the coupled-channel problems with an improved complex scaling method
Yan-Ke Chen, Lu Meng, Zi-Yang Lin, and Shi-Lin Zhu. Virtual states in the coupled-channel problems with an improved complex scaling method. Phys. Rev. D , 109(3):034006, 2024
2024
-
[19]
Leinweber, Zhan-wei Liu, and Anthony W
Jia-jun Wu, Derek B. Leinweber, Zhan-wei Liu, and Anthony W. Thomas. Structure of the Roper Reso- nance from Lattice QCD Constraints. Phys. Rev. D , 97(9):094509, 2018
2018
-
[20]
Continuum structure of few-body sys- tems
Sebastian Dietz. Continuum structure of few-body sys- tems. PhD thesis, Darmstadt, Tech. U., 2023
2023
-
[21]
Abell, Derek B
Curtis D. Abell, Derek B. Leinweber, Anthony W. Thomas, and Jia-Jun Wu. Regularization in nonpertur- bative extensions of effective field theory. Phys. Rev. D , 106(3):034506, 2022
2022
-
[22]
Two particle states and the S-matrix elements in multi-channel scattering
Song He, Xu Feng, and Chuan Liu. Two particle states and the S-matrix elements in multi-channel scattering. JHEP, 07:011, 2005
2005
-
[23]
Meissner, and Akaki Rusetsky
Michael Lage, Ulf-G. Meissner, and Akaki Rusetsky. A Method to measure the antikaon-nucleon scattering length in lattice QCD. Phys. Lett. B , 681:439–443, 2009
2009
-
[24]
Bernard, M
V. Bernard, M. Lage, U. G. Meissner, and A. Rusetsky. Scalar mesons in a finite volume. JHEP, 01:019, 2011
2011
-
[25]
Szczepaniak
Peng Guo, Jozef Dudek, Robert Edwards, and Adam P. Szczepaniak. Coupled-channel scattering on a torus. Phys. Rev. D , 88(1):014501, 2013
2013
-
[26]
Generalized L¨ uscher formula in multichannel baryon-meson scattering
Ning Li and Chuan Liu. Generalized L¨ uscher formula in multichannel baryon-meson scattering. Phys. Rev. D , 87(1):014502, 2013
2013
-
[27]
Nieves and E
J. Nieves and E. Ruiz Arriola. The S11 - N (1535) and - N (1650) resonances in meson baryon unitarized cou- pled channel chiral perturbation theory. Phys. Rev. D , 64:116008, 2001
2001
-
[28]
Hanhart, J
C. Hanhart, J. R. Pelaez, and G. Rios. Remarks on pole trajectories for resonances. Phys. Lett. B , 739:375–382, 2014
2014
-
[29]
New Insights on Low Energy πN Scattering Amplitudes
Yu-Fei Wang, De-Liang Yao, and Han-Qing Zheng. New Insights on Low Energy πN Scattering Amplitudes. Eur. Phys. J. C , 78(7):543, 2018
2018
-
[30]
M. Luscher. Volume Dependence of the Energy Spectrum in Massive Quantum Field Theories. 1. Stable Particle States. Commun. Math. Phys. , 104:177, 1986
1986
-
[31]
M. Luscher. Volume Dependence of the Energy Spectrum in Massive Quantum Field Theories. 2. Scattering States. Commun. Math. Phys. , 105:153–188, 1986
1986
-
[32]
Two particle states on a torus and their relation to the scattering matrix
Martin Luscher. Two particle states on a torus and their relation to the scattering matrix. Nucl. Phys. B , 354:531– 578, 1991
1991
-
[33]
Leinweber, Finn M
Zhan-Wei Liu, Waseem Kamleh, Derek B. Leinweber, Finn M. Stokes, Anthony W. Thomas, and Jia-Jun Wu. Hamiltonian effective field theory study of the N∗ (1440) resonance in lattice QCD. Phys. Rev. D , 95(3):034034, 2017
2017
-
[34]
J. M. M. Hall, A. C. P. Hsu, D. B. Leinweber, A. W. Thomas, and R. D. Young. Finite-volume matrix Hamil- 17 tonian model for a ∆ → N π system. Phys. Rev. D , 87(9):094510, 2013
2013
-
[35]
Jonathan M. M. Hall, Waseem Kamleh, Derek B. Lein- weber, Benjamin J. Menadue, Benjamin J. Owen, An- thony W. Thomas, and Ross D. Young. Lattice QCD Evidence that the Λ(1405) Resonance is an Antikaon- Nucleon Molecule. Phys. Rev. Lett. , 114(13):132002, 2015
2015
-
[36]
Leinweber, Finn M
Zhan-Wei Liu, Waseem Kamleh, Derek B. Leinweber, Finn M. Stokes, Anthony W. Thomas, and Jia-Jun Wu. Hamiltonian effective field theory study of the N ∗ (1535) resonance in lattice QCD. Phys. Rev. Lett. , 116(8):082004, 2016
2016
-
[37]
Abell, Derek B
Curtis D. Abell, Derek B. Leinweber, Anthony W. Thomas, and Jia-Jun Wu. Effects of multiple single- particle basis states in scattering systems. Annals Phys. , 459:169531, 2023
2023
-
[38]
Abell, Derek B
Curtis D. Abell, Derek B. Leinweber, Zhan-Wei Liu, An- thony W. Thomas, and Jia-Jun Wu. Low-lying odd- parity nucleon resonances as quark-model-like states. Phys. Rev. D , 108(9):094519, 2023
2023
-
[39]
Jia-Jun Wu, T. S. H. Lee, A. W. Thomas, and R. D. Young. Finite-volume Hamiltonian method for coupled- channels interactions in lattice QCD. Phys. Rev. C , 90(5):055206, 2014
2014
-
[40]
Three- neutron resonance trajectories for realistic interaction models
Rimantas Lazauskas and Jaume Carbonell. Three- neutron resonance trajectories for realistic interaction models. Phys. Rev. C , 71:044004, 2005
2005
-
[41]
Miguel Marqu´ es and Jaume Carbonell
F. Miguel Marqu´ es and Jaume Carbonell. The quest for light multineutron systems. Eur. Phys. J. A , 57(3):105, 2021
2021
-
[42]
New insight into the exotic states strongly coupled with the D ¯D∗ from the T + cc
Guang-Juan Wang, Zhi Yang, Jia-Jun Wu, Makoto Oka, and Shi-Lin Zhu. New insight into the exotic states strongly coupled with the D ¯D∗ from the T + cc. Sci. Bull. , 69:3036–3041, 2024
2024
-
[43]
Novel Coupled Channel Frame- work Connecting the Quark Model and Lattice QCD for the Near-threshold Ds States
Zhi Yang, Guang-Juan Wang, Jia-Jun Wu, Makoto Oka, and Shi-Lin Zhu. Novel Coupled Channel Frame- work Connecting the Quark Model and Lattice QCD for the Near-threshold Ds States. Phys. Rev. Lett. , 128(11):112001, 2022
2022
-
[44]
Jing Song, L. R. Dai, and E. Oset. How much is the com- positeness of a bound state constrained by a and r0? The role of the interaction range. Eur. Phys. J. A , 58(7):133, 2022
2022
Reviewed August 7, 2026 · model on record in the stance chip above.
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