REVIEW
Compositeness of near-threshold exotic hadrons in systems with Coulomb and short-range interactions
High Energy Physics - Phenomenology · Submitted 6 Oct 2026 · 19 references
Pith's verdict: A plausible regime criterion announced in a companion letter whose quantitative support all lives in the same authors' unreviewed preprint; useful and clearly framed, but not established on its own.
T0 · AI review
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Referee report
The paper
The paper claims
A single ratio — Coulomb effective range over Bohr radius — decides whether near-threshold hadron states stay composite-dominant despite long-range Coulomb forces.
The reading
What carries the argument
The argument runs through the Coulomb-distorted short-range scattering amplitude $f^{CS}(k)$ of Eq. (1), whose denominator contains the Coulomb scattering length $a_C^s$, the Coulomb effective range $r_C^e$, and the Coulomb term $-2 k_C H(\eta)$, together with the compositeness formula $X = [1 - r_C^e/R_C]^{-1}$, where $R_C$ is the wave-function length scale in the presence of Coulomb interaction. The load-bearing mechanism is the scale-separation window $1/a_B \ll k \ll 1/|r_C^e|$: when such a window exists, the pole is governed primarily by the scattering length and the short-range universality leaves a remnant that pushes $X$ toward unity.
Extended reading notes
Core claim
On the paper's own terms, the central claim is that the ratio $|r_C^e|/a_B$ of the Coulomb effective range to the Bohr radius determines whether a remnant of short-range low-energy universality survives in systems with Coulomb plus short-range interactions. In the weak-Coulomb regime $|r_C^e|/a_B \ll 1$, there is a momentum window $1/a_B \ll k \ll 1/|r_C^e|$ in which both the Coulomb term and the effective-range term in the Coulomb-distorted scattering amplitude are negligible, so the pole is set by the Coulomb scattering length; the compositeness of near-threshold bound states is then enhanced toward unity, and for repulsive Coulomb the bound state's composite-dominant nature persists into the resonance region across the threshold. In the strong-Coulomb regime $|r_C^e|/a_B \gg 1$, the Coulomb-dominant region is reached before the universal window can open, the enhancement disappears, and near-threshold states are not necessarily composite-dominant.
Load-bearing premise
The load-bearing premise is that a genuinely empty intermediate momentum window $1/a_B \ll k \ll 1/|r_C^e|$ exists in which the Coulomb form factor $-2 k_C H(\eta)$ is negligible; the paper infers this from the Bohr-radius scale but does not analyze $H(\eta)$ or verify that the Coulomb-modified effective-range expansion remains accurate there.
Editorial extensions
If this is right
- The ratio $|r_C^e|/a_B$ becomes a quantitative screening criterion: candidates with $|r_C^e|/a_B \ll 1$ can be treated under short-range universality, while those with the ratio of order one or larger require Coulomb-corrected structure analyses.
- For repulsive Coulomb systems in the weak-Coulomb regime, near-threshold resonances inherit the composite-dominant nature of the connected bound state across the threshold, extending the universal expectation into the resonance region.
- For attractive Coulomb systems, the compositeness approaches unity at the pure Coulomb ground state regardless of the effective range, and does so faster in the weak-Coulomb regime.
- Systems of the 8Be type, where switching off Coulomb repulsion turns a near-threshold resonance into a bound state, illustrate the qualitative sensitivity of the pole structure to the long-range force that this scheme aims to characterize.
Reading between the lines
- The criterion could serve as a red flag in experimental searches: a narrow near-threshold candidate with $|r_C^e|/a_B$ of order one or larger should not be assumed composite-dominant without explicitly accounting for Coulomb distortions.
- The composite-dominant conclusion for repulsive-Coulomb resonances depends on the specific interpretation prescription applied to the complex compositeness; a different prescription could shift that reading.
- The same scale-separation logic may extend to other long-range power-law forces, such as dipole or van der Waals interactions, with an analogous dimensionless ratio controlling the surviving remnant of universality.
Original abstract
We study the universal properties of near-threshold $s$-wave eigenstates in systems with Coulomb plus short-range interactions by analyzing their compositeness. Using a nonrelativistic effective field theory, we derive a relation between the compositeness of near-threshold states and the Coulomb scattering length, the Coulomb effective range, and the Bohr radius. We find that the long-range Coulomb interaction modifies the threshold behavior expected from the low-energy universality of purely short-range systems. When the Coulomb interaction is relatively weak compared with the short-range interaction, a remnant of the low-energy universality associated with the short-range interaction survives, leading to composite-dominant near-threshold eigenstates. In contrast, in the strong-Coulomb regime, this remnant disappears.
The compiled record
The paper's own sentences, arranged, kept beside the review and separate from it. Each label is drawn from a closed vocabulary; the number beside it is the probability the classifier gave that label. Numbers in the tables are the authors', checked by code. No sentence in this record was written by a model.
The abstract, sentence by sentence
We study the universal properties of near-threshold $s$-wave eigenstates in systems with Coulomb plus short-range interactions by analyzing their compositeness. Using a nonrelativistic effective field theory, we derive a relation between the compositeness of near-threshold states and the Coulomb scattering length, the Coulomb effective range, and the Bohr radius. We find that the long-range Coulomb interaction modifies the threshold behavior expected from the low-energy universality of purely short-range systems. When the Coulomb interaction is relatively weak compared with the short-range interaction, a remnant of the low-energy universality associated with the short-range interaction survives, leading to composite-dominant near-threshold eigenstates. In contrast, in the strong-Coulomb regime, this remnant disappears.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | We study the universal properties of near-threshold $s$-wave eigenstates in systems with Coulomb plus short-range interactions by analyzing their compositeness. | contribution 0.99 | 0.94 | 0.07 | asserted 0.81 |
| s1 | Using a nonrelativistic effective field theory, we derive a relation between the compositeness of near-threshold states and the Coulomb scattering length, the Coulomb effective range, and the Bohr radius. | method 0.66 | 0.96 | 0.13 | asserted 1.00 |
| s2 | We find that the long-range Coulomb interaction modifies the threshold behavior expected from the low-energy universality of purely short-range systems. | result 0.97 | 0.94 | 0.31 | asserted 1.00 |
| s3 | When the Coulomb interaction is relatively weak compared with the short-range interaction, a remnant of the low-energy universality associated with the short-range interaction survives, leading to composite-dominant near-threshold eigenstates. | result 0.88 | 0.89 | 0.35 | asserted 0.99 |
| s4 | In contrast, in the strong-Coulomb regime, this remnant disappears. | result 0.98 | 0.86 | 0.16 | asserted 1.00 |
What was examined, and what was not
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References
Discussion
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