Non perturbative chiral approach to s-wave \bar{K}N interactions

A. Ramos (Universitat de Barcelona); E. Oset (Universidad de Valencia)

REVIEW

Non perturbative chiral approach to s-wave \bar{K}N interactions

E. Oset (Universidad de Valencia), A. Ramos (Universitat de Barcelona)

Nuclear Theory · Submitted 11 Nov 1997 · 34 references

Pith's verdict: The eta-channel result is real physics and the unfitted cross sections are the strongest part, but the necessity claim rests on a single no-eta parameter point rather than a refit.

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arXiv IDnucl-th/9711022 (version 1)

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CitationA. Ramos (Universitat de Barcelona), E. Oset (Universidad de Valencia). "Non perturbative chiral approach to s-wave \bar{K}N interactions." arXiv:nucl-th/9711022 (1997). https://pith.science/paper/JRFOGEWN

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Significance

If the central claim holds, this is a genuinely economical result: the entire low-energy S = -1 meson-baryon data set, including a dynamically generated resonance, follows from the leading-order chiral Lagrangian with two parameters, one of which (f) sits between f_π and f_K where it is expected to sit. The methodological point that the off-shell potential collapses into a coupling renormalization, reducing the LS equations to matrix algebra, is reusable and was subsequently widely adopted. Two features deserve explicit credit. First, the cross sections in Figs. 3-8 were not used in the fit, so they are honest post-dictions rather than fitted curves, and the agreement in the K⁻p, K̄⁰n, π⁺Σ⁻ and π⁰Σ⁰ channels is good. Second, the paper makes falsifiable statements that were testable at the time: the K⁻p scattering length, the K⁻n scattering length, the vanishing S = 1, T = 0 scattering length, and the S = 1, T = 1 phase shifts, all of which are compared with independent data and with the kaonic hydrogen measurement of [27]. The comparison of Table VII with [27] and [28] is a real prediction, not a fit.

Major objections (4)

[§VII and Table VI] The headline claim of the abstract (abstract:s2) and of §VIII — that including the ηΛ and ηΣ⁰ channels 'allows a solution in terms of only the lowest order Lagrangian' — rests on a single comparison in Table VI: γ = 1.05 with the η channels removed versus 2.33 with them, against 2.36 ± 0.04 experimentally. The no-η entry is evaluated at the same f = 1.15 f_π and qmax = 630 MeV as the full fit, so it is not a best fit of the no-η model. The paper acknowledges the refit question in §VII ('Obviously one can choose other values of f and qmax to reproduce the mass distribution without the η channels') and answers it by citing [8] and 'corroborated here'; but [8] is a five-parameter model with next-to-leading-order Lagrangians and therefore does not settle the no-η leading-order case, and the corroboration 'here' is the one parameter point. Since γ is one of the three fitted quantities, the necessity claim is precisely the statement that no (f, qmax) reproduces γ, Rc, Rn and the Λ(1405) peak in the no-η model, and that two-parameter optimization is never performed. A scan over f and qmax for the no-η system, reported as a contour or a table of (γ, Rc, Rn, M_Λ), would settle it. If some point reaches γ ≈ 2.0-2.4 with acceptable Rc, Rn and a peak near 1405 MeV, the wording should be softened from 'very important'/'allows' to 'improves'.
[§I versus §VII] §I states that the aim is to describe the data 'in terms of the lowest order chiral Lagrangian (with no free parameters) and one cut off', and the abstract's 'only the lowest order Lagrangian' carries the same implication. §VII, however, fits two quantities: qmax and f, the latter moved to 1.15 f_π. The paper is internally aware of this ('Our free parameter is qmax, but we allow also some small variation of f'), but the 'no free parameters' phrasing in §I and the abstract is not consistent with the fit actually performed. The parameter count should be stated as two (f, qmax) throughout, with the remark that f = 1.15 f_π lies between f_π and f_K = 1.22 f_π and is therefore a reasonable renormalization rather than an arbitrary fit parameter. This matters because the economy of the scheme relative to [8] is part of the paper's selling point, and the current phrasing overstates it.
[§V, Eqs. (17)-(21)] The reduction of the coupled Lippmann-Schwinger equations to the algebraic T = [1 − VG]⁻¹V is justified in Eqs. (17)-(18) by a one-loop, equal-mass, heavy-baryon estimate showing that the off-shell part of the potential renormalizes f, followed by 'we can extend these arguments to higher order loops'. The extension to all loops and to the eight-channel system with unequal masses is asserted, not shown. The alternative reading in Eqs. (22)-(25) makes the same point from the optical theorem and concedes that the cutoff is chosen so that Re T₂ ≃ V Re G V, an approximation justified only a posteriori by the quality of the fit. Because f is fitted, part of the off-shell ambiguity is absorbed into it, which limits the practical damage; nevertheless the manuscript should state explicitly that Eq. (19) is an approximation to Eq. (15), and should give an estimate of its size — for instance by comparing the full LS solution with the algebraic one in a two-channel truncation, or by varying the off-shell treatment and quoting the spread in γ and in the K⁻p scattering length.
[§V, Eq. (26), and §VII] The ηΛ and ηΣ⁰ channels open about 180 MeV above the K⁻p threshold, so throughout the fitted region they are far off shell and their contribution enters only through the analytically continued k₀ of Eq. (26). Yet they are credited with changing γ by a factor 2.2 and the K⁻p → π⁻Σ⁺ cross section by a factor of three. The mechanism deserves a sentence or two: whether the effect comes through the real part of the η-channel G function, through the coupled-channel inversion, or through the specific continuation prescription of Eq. (26). A stability check — varying the continuation prescription or the η-channel cutoff and quoting the resulting change in γ — would make the claim much harder to dismiss, given that it carries the paper's main message.

Minor objections (8)

[Tables I-V] As printed, the coefficient matrices in Tables I-V are incomplete: several rows and columns are blank or truncated (for example the π⁰Λ row of Table I is all zeros, and the upper triangles of Tables II-V are largely missing). Since these matrices are the entire input to the calculation, the full symmetric matrices should be given explicitly, or the reader should be referred to a complete listing.
[§VII and Table VII] The errors quoted for the kaonic hydrogen result of [27] differ between the text ('(−0.78 ± 0.15 ± 0.03) + i(0.49 ± 0.25 ± 0.12) fm') and Table VII ('(−0.78 ± 0.18) + i(0.49 ± 0.37)'). These should be made consistent.
[§VII] The statement that the K⁻p scattering length is 'essentially in agreement' with [27] is generous: the real part agrees well, but the imaginary part, 0.97 fm in the full basis, is about twice the measured 0.49 fm. The comparison should be qualified rather than described as agreement.
[§VII and Table VI] The text says the three threshold ratios are 'reproduced within 5%', but Rc = 0.640 against 0.664 ± 0.011 and Rn = 0.217 against 0.189 ± 0.015 are each roughly two standard deviations away. A χ² or an explicit statement of the deviations in units of the experimental error would be more informative than a percentage.
[§V, Eqs. (22)-(25)] The reinterpretation of the on-shell factorization via the optical theorem is attributed to [13], which is listed as an unpublished Valencia preprint. Since this passage supplies the conceptual justification for the central approximation, either the argument should be made self-contained here or the citation should be updated to a published version.
[Fig. 2] The caption does not state which parameters were used for the long-dashed (no-η) curve. If they are the same f and qmax as the full calculation, this should be said explicitly, since the reader will otherwise assume the no-η curve is a best fit.
[Abstract] The abstract lists 'π⁰Σ' among the reproduced channels, whereas the text and figures distinguish π⁰Σ⁰. The notation should be made uniform.
[Throughout] There are numerous typographical errors that should be corrected: 'succesfully', 'idoneous', 'appropiate', 'wich', 'not not been used', 'Shoud', 'fnantial', 'Un iversitat', and 'were p, p′' for 'where p, p′'.

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The paper

The paper claims

Including the eta-Lambda and eta-Sigma0 channels lets the lowest-order chiral Lagrangian alone reproduce the S = -1 meson-baryon data, including the Lambda(1405) and the threshold branching ratios, with one cutoff as the only free parameter

The reading

The paper asks whether the strong low-energy kaon-nucleon sector — the place where ordinary chiral perturbation theory breaks down because a resonance, the $S=-1$ s-wave $J^P = 1/2^-$ state, sits just below the $K^-p$ threshold — can be described without importing higher-order chiral counterterms. The authors solve coupled-channel Lippmann-Schwinger equations in eight physical channels ($K^-p$, $K^0n$, $K^-n$-type states, $K^+N$ states, $K^0p$, $K^+p$, $K^+n$, and the $S=-1$ $T=2$ channel) using the leading-order Lagrangian as the potential and a single momentum cutoff $q_{max}$ to regularize the loop. Earlier work along these lines needed five parameters from the second-order Lagrangian and still missed the threshold branching ratios; the authors report that adding the two eta channels, $K^-p$ and $K^0n$, closes that gap. If correct, this says the $S=-1$ meson-baryon data are already encoded in chiral symmetry at leading order, with the cutoff absorbing whatever the higher orders would have contributed.

What carries the argument

The machinery is the on-shell factorization of the coupled Lippmann-Schwinger equations into the algebraic form $T = [1 - VG]^{-1} V$, where $V$ is the leading-order chiral potential $V_{ij} = -C_{ij}(k^0 + k'^0)/(4f^2)$ built from the coefficients in the paper's tables, and $G$ is a diagonal loop function regularized by a sharp cutoff $q_{max}$. The argument that lets the integral equation collapse to a matrix inversion is that the off-shell part of $V$ only reshapes the coupling $f$ at one loop and can therefore be absorbed into the physical $f$; the authors also present the inverse-amplitude reading, in which the cutoff is chosen so that the real part of the second-order amplitude is approximated by $V(Re G)V$. The eta channels enter as analytically continued potentials below their thresholds via $k^0 = (s + m_eta^2 - M_B^2)/(2 sqrt(s))$, and their inclusion reshapes the interference between the real parts of the amplitudes across all channels.

Extended reading notes

Core claim

The central claim is that the eight-channel system, with the $K^+N$ and $K^0p$ channels included, reproduces the $S=-1$ data using only the lowest-order chiral Lagrangian. The quantitative core is the threshold branching ratio $K^+N$: omitting the eta channels gives $K^+N$, while the full basis gives $K^+N$, against the measured $K^+N$. The fit proceeds in two steps — $f$ is held near $f_0$ and $q_{max}$ is varied to match the three threshold ratios, then $f$ is chosen to reproduce the position and shape of the $K^+N$ peak in the $K^+N$ mass spectrum; the optimal point is $f = 1.15 f_0$ and $q_{max} = 630$ MeV. The cross sections for $K^-p$ elastic, charge exchange, and the four pionic channels are then predictions, not fit inputs, and they agree with the low-energy data. The authors also report scattering lengths, $a(K^-p) = -0.99 + i0.97$ fm and $a(K^-n) = 0.53 + i0.61$ fm, close to the values extracted from kaonic hydrogen X-rays and from dispersion-relation analyses.

Load-bearing premise

The load-bearing premise is that the off-shell part of the chiral potential does nothing except renormalize the coupling $f$, so that the full coupled integral equations can be replaced by the algebraic matrix inversion $T = [1-VG]^{-1}V$; the paper argues this at one loop with equal masses and then extends it to all loops and all eight channels by assertion rather than demonstration.

Editorial extensions

If this is right

The $S=-1$ meson-baryon data, including the $\Lambda(1405)$, need no second-order chiral counterterms — one cutoff and a modest renormalization of $f$ suffice.
The ratio $\gamma = \Gamma(K^-p \to \pi^+\Sigma^-)/\Gamma(K^-p \to \pi^-\Sigma^+)$, which vanishes at leading order, becomes $2.33$ against a measured $2.36 \pm 0.04$ once the eta channels are in the loop.
The $K^-p \to \pi^-\Sigma^+$ cross section near threshold drops by roughly a factor of three when the eta channels are included, so any extraction of this channel's rate that neglects them is off by that much.
The resulting $K^-p$ and $K^-n$ scattering lengths sit close to the kaonic-hydrogen and dispersion-relation determinations, so the same amplitudes can be carried into kaon propagation in nuclear matter.
The $S=1$ sector comes out only fairly: the $T=1$ phase shifts are somewhat small in magnitude, and $a(S=1,T=1) = -0.26$ fm undershoots the measured $-0.32 \pm 0.02$ fm.

Reading between the lines

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

If the eta channels matter this much in $S=-1$, the same channels should be re-examined wherever they were dropped as kinematically closed — for instance in kaon-nucleus optical potentials and in fits to $K^-$-nucleus level shifts.
The success of a single cutoff suggests a practical test: refit the meson-baryon sector channel by channel and see whether one $q_{max}$ survives, which would indicate the cutoff is standing in for a genuine scale rather than absorbing channel-specific data.
The claim that off-shell pieces only renormalize $f$ could be checked directly by solving the full eight-channel integral equation numerically and comparing the resulting $T$-matrix poles and threshold ratios to the algebraic ones.

Original abstract

The s-wave meson-nucleon interaction in the $S = -1$ sector is studied by means of coupled-channel Lippmann Schwinger equations, using the lowest order chiral Lagrangian and a cut off to regularize the loop integrals. The method reproduces succesfully the $\Lambda (1405)$ resonance and the $K^- p \to K^- p, \bar{K}^0 n, \pi^0 \Lambda, \pi^0 \Sigma, \pi^+ \Sigma^-, \pi^- \Sigma^+$ cross sections at low energies. The inclusion of the $\eta \Lambda, \eta \Sigma^0$ channels in the coupled system is found very important and allows a solution in terms of only the lowest order Lagrangian.

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.

Compiled by classifier-1.13.0 via TypeSafe API, question bank abstract-p1-20260923, 2026-09-23: 1 request, 3,179 input tokens.

What the abstract itself states, as probabilities: claims first 0.03 · states limitation 0.17 · human participants 0.01 · controlled comparison 0.03 · randomized assignment 0.01 · states quantitative result 0.18 · compares with prior results 0.19 · mentions code or data availability 0.02.

The abstract, sentence by sentence

arXiv listing abstract v1. Results and the main claim are underlined; show every role.

The s-wave meson-nucleon interaction in the $S = -1$ sector is studied by means of coupled-channel Lippmann Schwinger equations, using the lowest order chiral Lagrangian and a cut off to regularize the loop integrals. The method reproduces succesfully the $\Lambda (1405)$ resonance and the $K^- p \to K^- p, \bar{K}^0 n, \pi^0 \Lambda, \pi^0 \Sigma, \pi^+ \Sigma^-, \pi^- \Sigma^+$ cross sections at low energies. The inclusion of the $\eta \Lambda, \eta \Sigma^0$ channels in the coupled system is found very important and allows a solution in terms of only the lowest order Lagrangian.

background contribution method result interpretation main claim

What the classifier reports for each sentence. The number is the probability it gave the label.
#	sentence	role	the authors' own work	states the main conclusion	strength
s0	The s-wave meson-nucleon interaction in the $S = -1$ sector is studied by means of coupled-channel Lippmann Schwinger equations, using the lowest order chiral Lagrangian and a cut off to regularize the loop integrals.	method 0.94	0.89	0.06	asserted 0.99
s1	The method reproduces succesfully the $\Lambda (1405)$ resonance and the $K^- p \to K^- p, \bar{K}^0 n, \pi^0 \Lambda, \pi^0 \Sigma, \pi^+ \Sigma^-, \pi^- \Sigma^+$ cross sections at low energies.	result 1.00	0.90	0.43	asserted 1.00
s2	The inclusion of the $\eta \Lambda, \eta \Sigma^0$ channels in the coupled system is found very important and allows a solution in terms of only the lowest order Lagrangian.	result 0.92	0.93	0.37	asserted 1.00

What kind of paper the classifier reports this is: theoretical result 0.72 · evidence from simulation or computation 0.99.

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arXiv listing abstract v1

not examined

full text
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Every quoted sentence on this record is the authors'. Every label is from Pith's closed vocabulary, with the probability shown beside it. Every number in the measurements table is the authors', checked by code. Record as JSON

Figures

**Figure 1.** FIG. 1. Diagrammatic representation of the Lippmann Schwin

**Figure 4.** FIG. 4. Same as fig. 3 for

**Figure 5.** FIG. 5. Same as fig. 3 for

**Figure 6.** FIG. 6. Same as fig. 3 for

**Figure 7.** FIG. 7. Same as fig. 3 for

**Figure 8.** FIG. 8. Same as fig. 3 for

**Figure 9.** FIG. 9. Scattering amplitudes for

**Figure 10.** FIG. 10. S-wave phase shifts for

**Figure 11.** FIG. 11. S-wave phase shifts for

Showing 9 of the paper's 11 figures. See all figures in the PDF ↗ Figures reproduced from arXiv:nucl-th/9711022 by the authors.

References

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C. H. Lee, G. E. Brown, D. P. Min and M. Rho, Nucl. Phys. A38 5 (1995) 481 20 TABLES TABLE I. Cij coeﬃcients of eq. (7). Cji = Cij. K −p ¯K 0n π 0Λ π0Σ0 ηΛ ηΣ0 π+Σ− π−Σ+ K −p 2 1 √ 3 2 1 2 3 2 √ 3 2 0 1 ¯K 0n 2 − √ 3 2 1 2 3 2 − √ 3 2 1 0 π0Λ 0 0 0 0 0 0 π0Σ0 0 0 0 2 2 ηΛ 0 0 0 0 ηΣ0 0 0 0 π+Σ− 2 0 π−Σ+ 2 TABLE II. Dij coeﬃcients of eq. (9) for T = 0. Dji...

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−0.97 + i1.1 exp. [27] (−0.78 ± 0.18) + i(0.49 ± 0.37) exp. [28] −0.67 + i0.64 0 .37 + i0.60 exp. Re (a) [28] −0.98 0 .54 23 FIGURES k k’ p p’ k q k’ p p’ + + + . . . FIG. 1. Diagrammatic representation of the Lippmann Schwin ger equations, eq. (15), in ¯KN scattering. 24 FIG. 2. The πΣ mass distribution around the Λ(1405) resonance from eq. (2 7). Short-...

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hep-ph 1998-04 conditional novelty 6.0 of 10

Unitarized coupled-channel chiral perturbation theory with seven fitted fourth-order low-energy constants reproduces meson-meson phase shifts to 1.2 GeV and generates poles for the sigma, kappa, f0, a0, rho, K* and phi.
Revisiting the $\Lambda(1405)$ pole structure with convolutional neural networks
hep-ph 2026-08 reject novelty 5.0 of 10

A CNN ensemble trained on synthetic uniformized S-matrix lineshapes classifies the CLAS Lambda(1405) data as globally dominated by a three-pole [2bt,1bb,0tb] structure, implying a two-state system.
Role of the $\Sigma(1430)(1/2^-)$ in the $J/\psi \to \Lambda \bar{\Lambda} \pi^0$ reaction
hep-ph 2026-07 conditional novelty 5.0 of 10

The isospin-violating J/ψ→ΛΛ̄π⁰ decay is shown to selectively produce the dynamically-generated Σ(1430) resonance while suppressing the conventional Σ(1385) state, matching limited BESIII data.
Nature of the newly found $\Omega(2109)$
hep-ph 2026-06 unverdicted novelty 5.0 of 10

Coupled-channel calculations in K- Ξ0, K̄0 Ξ-, K*- Ξ0 and K̄*0 Ξ- channels generate an isoscalar 1/2- resonance at 2109 MeV strongly correlated with the K̄* Ξ system.
Radiative decays of dynamically generated pentaquarks in the chiral unitary approach: the $P_c(4457)\to P_c(4312)\,\gamma$ transition
hep-ph 2026-06 unverdicted novelty 5.0 of 10

The M1 radiative decay width Pc(4457)(3/2-) → Pc(4312)(1/2-)γ is computed as 6.7 keV (range 2-9 keV) via 19 triangle loops with photon coupling to molecular components.
Finding Low Star Discrepancy 3D Kronecker Point Sets Using Algorithm Configuration Techniques
cs.NE 2026-04 unverdicted novelty 5.0 of 10

Optimizing the two Kronecker parameters with irace yields new state-of-the-art L∞ star discrepancy for 3D point sets of size at least 500 and for ranges of sizes.
Probing the isospin structure and low-lying resonances in $\Lambda_c^+ \to n\bar{K}^0 \pi^+$ decays
hep-ph 2026-02 unverdicted novelty 5.0 of 10

The chiral unitary calculation predicts a narrow peak from N(1535) in the pi+ n invariant mass spectrum and a dip from Lambda(1670) in the K0bar n spectrum, supporting the molecular interpretation of these resonances.
The dynamically generated $h_1$ state by the $K^*\bar{K}^*$ interaction and its $K_1(1270)\bar{K}$ and $b_1(1235)\pi$ decays
hep-ph 2026-01 conditional novelty 5.0 of 10

The dynamically generated h1(1790) K*Kbar* molecule is predicted to decay into K1(1270)Kbar and b1(1235)pi with partial widths of about 0.5 to several MeV, plus stable width ratios R1≈0.3 and R2≈0.53.
Correlation functions for $n\,\bar{D}_{s1}(2460)$ and $n\,\bar{D}_{s1}(2536)$
hep-ph 2025-08 conditional novelty 5.0 of 10

The neutron-D_{s1}(2460) and neutron-D_{s1}(2536) systems are predicted to have bound states, with correlation functions sensitive to the molecular structure of the D_{s1} mesons.
Final state interaction in the $\Lambda_b\to D^+D^- \Lambda,~D^0D_s^- p,~D_s^+D_s^-\Lambda$ reactions
hep-ph 2025-07 conditional novelty 5.0 of 10

Threshold enhancements in the Ds-p, Ds-Lambda, and related mass distributions of Lambda_b decays are predicted from final state interactions with molecular exotic states.
Off-shell ambiguities in correlation functions: strategies to minimize them
hep-ph 2025-06 conditional novelty 5.0 of 10

For meson-baryon pairs tied to the N*(1535), off-shell ambiguities change correlation functions by only 2-3% in chiral models, and can be partly absorbed by adjusting the source size.
Theoretical study of the $N(1535)$ in the process $\Lambda_c^+\to n\pi^+\pi^0$
hep-ph 2025-04 conditional novelty 5.0 of 10

The Lambda_c^+ -> n pi+ pi0 decay is predicted to show peaks near 1500 MeV in the pi0 n and pi+ n invariant mass spectra, tracing the dynamically generated N(1535) resonance.
Decays of $P_c$ into $J/\psi N$ and $\eta_cN$ with heavy quark spin symmetry
hep-ph 2019-07 conditional novelty 5.0 of 10

Heavy quark spin symmetry turns the seven predicted D-bar(*)-Sigma_c(*) molecular pentaquarks into a parameter-free set of J/psi N and eta_c N partial-width ratios, five of which exceed the Pc(4312) rate.
Exotic Hadrons from Heavy Ion Collisions
nucl-th 2017-02 conditional novelty 5.0 of 10

Coalescence and statistical models of heavy ion collisions predict that compact multiquark hadrons are produced about an order of magnitude less abundantly than hadronic molecules or ordinary excited states of the same mass.
$\bar{D}\Sigma^*_c$ and $\bar{D}^*\Sigma_c$ interactions and the LHCb hidden-charmed pentaquarks
hep-ph 2015-07 conditional novelty 5.0 of 10

The LHCb pentaquark candidates Pc(4380) and Pc(4450) are identified as $Dbar Sigma^*_c$ and $Dbar^* Sigma_c$ molecular bound states with spin-parity 3/2- and 5/2+, respectively.
Scattering lengths of Nambu-Goldstone bosons off $D$ mesons and dynamically generated heavy-light mesons
hep-ph 2013-09 conditional novelty 5.0 of 10

A relativistic unitarized chiral fit to lattice scattering lengths reproduces the D*s0(2317) as a dynamical bound state and predicts its spin and bottom-quark partners.
Wave functions of composite hadron states and relationship to couplings of scattering amplitudes for general partial waves
hep-ph 2012-02 conditional novelty 5.0 of 10

A generalized Weinberg compositeness sum rule, valid for any partial wave, coupled channels, and resonances, indicates the rho meson is mostly not a pion-pion composite.
Chiral dynamics of the S11(1535) and S11(1650) resonances revisited
nucl-th 2010-12 conditional novelty 5.0 of 10

Fitting only pion-nucleon data below 1.56 GeV with a second-order chiral contact potential generates poles for both S11 resonances but not for the S31(1620).
Dynamically Generated Open and Hidden Charm Meson Systems
hep-ph 2006-12 conditional novelty 5.0 of 10

A unitarized SU(4) coupled-channel model predicts a new narrow hidden-charm scalar meson near 3.7 GeV, mostly a D Dbar quasi-bound state.
Review of the ${\mathbf \Lambda}$(1405): A curious case of a strange-ness resonance
nucl-th 2020-09 conditional novelty 2.0 of 10

The Lambda(1405) is best described by two poles, a narrow one near 1420 MeV and a broad one near 1380 MeV, and this two-pole picture survives every modern model class once kaonic-hydrogen and CLAS photoproduction data...
Two-pole structures in QCD: Facts, not fantasy!
hep-ph 2020-05 accept novelty 2.0 of 10

The Lambda(1405) and the D*0(2300) are each two resonances rather than one, according to unitarized chiral perturbation theory checked against lattice QCD and LHCb data.
Strangeness in Nuclei and Neutron Stars
nucl-ex 2020-02 accept novelty 2.0 of 10

A comprehensive review of strangeness in nuclear matter: the two-pole Lambda(1405), kaon and antikaon potentials in dense matter, phi broadening, hyperon forces, and their role in neutron star interiors.
Heavy Hadrons in Nuclear Matter
hep-ph 2016-06 accept novelty 2.0 of 10

The review consolidates three decades of theory on charm and bottom hadrons in nuclear matter, organized by chiral symmetry and heavy quark spin symmetry, and reports where competing models agree and where they do not.

How later papers used it

114 later papers cite it

Evidence: substantial. 97 of the citing papers share no author with it, and 33 of those carry a confident label from Pith's citation classifier.

Pith read 17 of the 189 citing sentences, choosing only those whose citation markers point at this paper alone, and wrote the paraphrases from them. The summary, the counts, the evidence level, the links and the quotes come from code; the summary counts the papers listed below. A later paper is listed under a label when Pith's citation classifier gives one of its sentences that label at probability 0.8 or more (0.95 for support), Pith's reading finds that the citing paper itself did it, and a second check confirms the paraphrase against the sentence. This section lists uses only. It does not list criticism or disagreement, so their absence here says nothing about how the paper has been received. Papers that share an author with this one are listed apart, under "By the same authors". A quote is the citing authors' own sentence, shown when their paper's licence is CC BY, CC BY-SA or CC0. JSON

2 later papers by other authors are listed below: 1 used its method or tool and 1 used its data or values. 3 more papers by the same authors are listed: 2 used its method or tool and 1 used its data or values.

Uses its method or tool 3 of 36 papers with this label · 2 by the same authors

Used its matrix V as the kernel for the Bethe-Salpeter equation to obtain the unitary transition matrix of this paper.

Radiative decays of the $\Lambda(1520)$ as a dynamically generated resonance (2026) · 0.95 · paraphrased: the licence does not allow quoting

By the same authors

We use the model of Ref. [ref] (called Oset-Ramos later) taking the input of Table [ref].

$\Lambda(1405)$ mediated triangle singularity in the $K^-d\to p\Sigma^-$ reaction (2021) (same authors) · Results · 0.92
Obtained this one using the chiral unitary approach of this paper with the coupled channels K̅N, πΣ, ηΛ, KΞ.

Correlation function for the $p ~f_1(1285)$ interaction (2025) (same authors) · 0.99 · paraphrased: the licence does not allow quoting

Uses its data or values 2 of 5 papers with this label · 1 by the same authors

Took the symmetric coefficient matrix elements given in this paper's tables for the I=0 and I=1 sectors.

Study of the resonance contributions in the $\Xi_{b}^{-} \rightarrow pK^{-}K^{-}$ decay (2022) · 0.92 · paraphrased: the licence does not allow quoting

By the same authors

Used the values D+F=1.26 and D-F=0.33 from this paper for the coupling of the mesons to the ground state baryons.

Radiative decays of dynamically generated charmed baryons (2010) (same authors) · 0.88 · paraphrased: the licence does not allow quoting

How the literature uses it

103 arXiv papers cite this in 178 sentences

Each citing sentence is taken from the citing paper's LaTeX source and typed by Pith's classifier. A label appears at probability 0.8 or more (0.95 for support), a contest at 0.7 or more; the quoted words are the citing authors'. How each label was checked · JSON

Papers citing it · 104 sentences without a confident label

Uses its method or tool 35 papers

The amplitudes $t_BP, ηΛ$ that we use are obtained within the chiral unitary approach of Refs. [ref] , where the coupled channels considered are $K̅N$, $πΣ$, $ηΛ$, $K Ξ$ and the $T$ matrix is given by [equation] with the interaction kernel $V$ of the type: [equation] where $k^0$ and $k'^0$ are the energies of the incoming and outgoing mesons in the rest frame of the meson-baryon system.

$\Lambda(1670)$ production in the $\psi(3686) \to \Lambda \bar \Lambda \eta$ reaction · Formalism · 0.99
For the meson-baryon amplitudes we apply the so-called chiral unitary approach [ref] .

Production of hyperon resonances induced by kaon on a deuteron target · $K^- d$ Scattering amplitudes · 0.99
The required kernels, i.e., the potentials which describe the interaction of the different pairs of the system are calculated using chiral Lagrangians [ref] .

Searching for exotic states in the $N \pi K $ system · Formalism and Results · 0.81

Uses its data or values 5 papers

In Eqs. [ref] and [ref], the amplitudes and meson-baryon loop functions are taken directly from Refs. [ref] .

Role of the $\Sigma(1430)(1/2^-)$ in the $J/\psi \to \Lambda \bar{\Lambda} \pi^0$ reaction · Formalism · 0.87
The coefficient matrix elements $C_i j$ are symmetric, $C_ij=C_ji$, given in Table [ref] for the $I=0$ sector, and in Table [ref] for the $I=1$ sector, which are taken from Ref. [ref] .

Study of the resonance contributions in the $\Xi_{b}^{-} \rightarrow pK^{-}K^{-}$ decay · Formalism · 0.92
The explicit value of the coefficient $C_ij$ for the $$ scattering is given in Ref. [ref] .

Internal structure of resonant Lambda(1405) state in chiral dynamics · $$ in chiral dynamics · 0.89

Cites it as support 3 papers

In the baryon-meson picture where the flavor-flavor type interaction, , is employed, the peak appears because of the attraction in the N$$ channel [ref] .

Lambda(1405) as a Resonance in the Baryon-Meson Scattering Coupled to the q^3 State in a Quark Model · Summary · 0.98
The phenomenological success of the model with only $V_WT$ [ref] indicates that the chiral symmetry constraint indeed works in reality.

QCD and the Strange Baryon Spectrum · Chiral SU(3) dynamics · 1.00
This is consistent with the dominance of the LO contribution observed in previous works [ref] .

Pole trajectories of the $\Lambda(1405)$ helps establish its dynamical nature · Results and discussions · 0.96

Cites it as background 26 papers

This can be mainly attributed to the two-pole structure predicted in the chiral unitary approach, which refers to a lower pole above the $πΣ$ threshold and a higher pole below the $K̅N$ threshold [ref] .

Pole trajectories of the $\Lambda(1405)$ helps establish its dynamical nature · Introduction · 0.82
In this work, we first provide a brief introduction of the $K̅N$ and related channel interactions within the chiral unitary approach [ref] .

How to unravel the nature of the $\Sigma^*(1430) (1/2^-)$ state from correlation functions · Summary of the chiral unitary approach for $K̅N$ in coupled channels · 0.95
The modern theory concerning the $Λ(1405)$ is the coupled-channel theory constrained by chiral and SU(3) flavor symmetry as well as unitarity [ref] .

Identifying the two-pole structure of the $\Lambda(1405)$ using an SU(3) flavor filter · Introduction · 0.90

Discussion

Disagree with the review, or know something it missed? Leave a comment, highlight any passage above to comment on it, or challenge this review formally.

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C. H. Lee, G. E. Brown, D. P. Min and M. Rho, Nucl. Phys. A38 5 (1995) 481 20 TABLES TABLE I. Cij coeﬃcients of eq. (7). Cji = Cij. K −p ¯K 0n π 0Λ π0Σ0 ηΛ ηΣ0 π+Σ− π−Σ+ K −p 2 1 √ 3 2 1 2 3 2 √ 3 2 0 1 ¯K 0n 2 − √ 3 2 1 2 3 2 − √ 3 2 1 0 π0Λ 0 0 0 0 0 0 π0Σ0 0 0 0 2 2 ηΛ 0 0 0 0 ηΣ0 0 0 0 π+Σ− 2 0 π−Σ+ 2 TABLE II. Dij coeﬃcients of eq. (9) for T = 0. Dji...

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−0.97 + i1.1 exp. [27] (−0.78 ± 0.18) + i(0.49 ± 0.37) exp. [28] −0.67 + i0.64 0 .37 + i0.60 exp. Re (a) [28] −0.98 0 .54 23 FIGURES k k’ p p’ k q k’ p p’ + + + . . . FIG. 1. Diagrammatic representation of the Lippmann Schwin ger equations, eq. (15), in ¯KN scattering. 24 FIG. 2. The πΣ mass distribution around the Λ(1405) resonance from eq. (2 7). Short-...

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