REVIEW
Bethe-Salpeter Study of Vector Meson Masses and Decay Constants
Nuclear Theory · Submitted 26 May 1999 · 34 references
Pith's verdict: A solid, honest extension of the Maris-Roberts DSE-BSE program to vector mesons; the physics is real, but the abstract's blanket 5%/10% claim is only true for the middle parameter set.
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Referee report
The paper
The paper claims
Fixing a quark model on pions and kaons, the authors predict rho, phi and K-star masses and decay constants without further tuning.
The reading
What carries the argument
The load-bearing device is the ladder-rainbow truncation: the Bethe–Salpeter kernel is a single dressed-gluon exchange with a bare quark-gluon vertex, matched to a rainbow truncation of the quark self-energy, so that the axial Ward–Takahashi identity survives and the pion is massless in the chiral limit. The interaction is a model two-point gluon function, Eq. (10), consisting of a finite-width Gaussian infrared term plus a one-loop renormalization-group tail that takes over above roughly 2 GeV$^2$. The vector amplitude is expanded on eight transverse, Dirac-trace-orthonormal covariants built from $gamma_mu$, the relative momentum $q$ and the total momentum $P$, then projected back onto that basis to give eight coupled integral equations; the angle dependence is handled either by direct two-variable discretization or by a Chebyshev expansion in $cos theta$. A separate asymptotic analysis, replacing the running coupling by its value at the larger momentum and converting the integral equations into differential equations, shows that the individual $1/q^2$ falloff of $F_1$, $F_2$ and $F_3$ would make the decay-constant integral logarithmically divergent, but the coefficients cancel once the second Chebyshev moment of $F_1$ is included — a concrete realization of the renormalizability the truncation is built to preserve.
Extended reading notes
Core claim
Solving the vector Bethe–Salpeter equation with all eight transverse Dirac covariants and the full angular dependence of the amplitudes, the authors find that the ladder-rainbow Dyson–Schwinger/Bethe–Salpeter framework, with parameters fixed only in the pseudoscalar sector, reproduces the ground-state vector meson spectrum and decay constants to within roughly 5% and 10% respectively. Concretely, for the middle parameter set, $m_rho = 0.742$ GeV against 0.770 measured, $m_phi = 1.072$ against 1.020, $m_K^star = 0.936$ against 0.892, with $f_rho = 0.207$ GeV against 0.216. The results are stable across three different widths of the modelled infrared interaction, so long as each is refitted to the same pion and kaon data. The authors also report a structural finding: only five of the eight covariants matter quantitatively for these observables, dropping the other three shifts masses by about 2% and decay constants by about 8%, and for the $rho$ and $phi$ the leading Chebyshev moment of each amplitude nearly suffices — except that the second moment of $F_1$ is required for the decay-constant loop integral to converge.
Load-bearing premise
The single modelled gluon interaction — a finite-width Gaussian infrared bump joined to a perturbative tail — is assumed to represent the quark-gluon interaction accurately enough over the larger and partly complex momentum range that the heavier vector bound states sample, even though its infrared width is a hand-chosen parameter and the earlier sharp delta-function form had to be discarded because it produced non-analytic quark propagators that spoiled the vector solutions.
Editorial extensions
If this is right
- Vector meson masses and decay constants can be obtained from a framework whose only inputs are pseudoscalar observables, so the vector sector becomes a genuine test of the truncation rather than a fit.
- The relative weight of the eight covariants is now known, which gives a practical recipe: keep $F_1$ through $F_5$ and the leading Chebyshev moments for $rho$ and $phi$, but add the second moment of $F_1$ before computing decay constants.
- Because the ladder kernel is $P$-independent, physical observables turn out independent of how momentum is shared between the quark and antiquark, but only when all relevant covariants and the full angular dependence are retained; truncating either reintroduces a spurious dependence of up to 5%.
- The calculated Bethe–Salpeter amplitudes can be fed directly into later calculations of $rho to pi pi$, $phi to K K$, $rho to pi gamma$ and electromagnetic form factors, replacing phenomenological amplitude ansätze.
- The same amplitudes provide a starting point for estimating meson-loop corrections, which are expected to shift the $rho$ mass by a few percent and could contribute to the $rho$–$omega$ splitting that the ladder truncation cannot produce.
Reading between the lines
- The out-of-sample agreement is the kind of check that separates a model with predictive content from a model with enough freedom to absorb any data; a natural next test is to fix parameters on pions and kaons and then predict a channel with no adjustable freedom at all, such as the axial-vector or scalar mesons, where the same ladder kernel is expected to do worse.
- The finding that five of eight covariants carry the physics suggests that a reduced, well-chosen amplitude basis could make vector-meson calculations cheap enough for finite-temperature or finite-density studies, where the full two-variable problem is currently out of reach.
- The cancellation that renders the decay-constant integral finite is a numerical fingerprint of the Ward-identity-preserving truncation; a truncation that broke that coordination would show a residual logarithmic divergence, which offers a cheap diagnostic for future kernel improvements.
- Since the $rho$–$omega$ degeneracy here is an artifact of the ladder kernel, any future calculation that reproduces this spectrum but also splits the two must be adding physics — meson loops or quark annihilation — beyond single-gluon exchange, and the size of that split is a direct measure of how much.
Original abstract
The masses and decay constants of the light vector mesons $\rho/\omega$, $\phi$ and $K^\star$ are studied within a ladder-rainbow truncation of the coupled Dyson-Schwinger and Bethe-Salpeter equations of QCD with a model 2-point gluon function. The approach is consistent with quark and gluon confinement, reproduces the correct one-loop renormalization group behavior of QCD, generates dynamical chiral symmetry breaking, and preserves the relevant Ward identities. The one phenomenological parameter and two current quark masses are fixed by requiring that the calculated $f_\pi, m_\pi$ and $m_K$ are correct. The resulting $f_K$ is within 3% of the experimental value. For the vector mesons, all eight transverse covariants are included and the dominant ones are identified; the complete angle dependence of the amplitudes is also retained. The calculated values for the masses $m_\rho, m_\phi$ and $m_{K^\star}$ are within 5%, while the decay constants $f_\rho, f_\phi$ and $f_{K^\star}$ for electromagnetic and leptonic decays are within 10% of the experimental values.
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
The masses and decay constants of the light vector mesons $\rho/\omega$, $\phi$ and $K^\star$ are studied within a ladder-rainbow truncation of the coupled Dyson-Schwinger and Bethe-Salpeter equations of QCD with a model 2-point gluon function. The approach is consistent with quark and gluon confinement, reproduces the correct one-loop renormalization group behavior of QCD, generates dynamical chiral symmetry breaking, and preserves the relevant Ward identities. The one phenomenological parameter and two current quark masses are fixed by requiring that the calculated $f_\pi, m_\pi$ and $m_K$ are correct. The resulting $f_K$ is within 3% of the experimental value. For the vector mesons, all eight transverse covariants are included and the dominant ones are identified; the complete angle dependence of the amplitudes is also retained. The calculated values for the masses $m_\rho, m_\phi$ and $m_{K^\star}$ are within 5%, while the decay constants $f_\rho, f_\phi$ and $f_{K^\star}$ for electromagnetic and leptonic decays are within 10% of the experimental values.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | The masses and decay constants of the light vector mesons $\rho/\omega$, $\phi$ and $K^\star$ are studied within a ladder-rainbow truncation of the coupled Dyson-Schwinger and Bethe-Salpeter equations of QCD with a model 2-point gluon function. | contribution 0.93 | 0.93 | 0.08 | asserted 0.99 |
| s1 | The approach is consistent with quark and gluon confinement, reproduces the correct one-loop renormalization group behavior of QCD, generates dynamical chiral symmetry breaking, and preserves the relevant Ward identities. | method 0.52 | 0.73 | 0.09 | asserted 0.80 |
| s2 | The one phenomenological parameter and two current quark masses are fixed by requiring that the calculated $f_\pi, m_\pi$ and $m_K$ are correct. | method 1.00 | 0.87 | 0.04 | asserted 0.99 |
| s3 | The resulting $f_K$ is within 3% of the experimental value. | result 1.00 | 0.94 | 0.10 | asserted 1.00 |
| s4 | For the vector mesons, all eight transverse covariants are included and the dominant ones are identified; the complete angle dependence of the amplitudes is also retained. | method 0.94 | 0.93 | 0.04 | asserted 1.00 |
| s5 | The calculated values for the masses $m_\rho, m_\phi$ and $m_{K^\star}$ are within 5%, while the decay constants $f_\rho, f_\phi$ and $f_{K^\star}$ for electromagnetic and leptonic decays are within 10% of the experimental values. | result 1.00 | 0.96 | 0.72 | asserted 1.00 |
What was examined, and what was not
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Figures
Figures reproduced from arXiv:nucl-th/9905056 by the authors.
References
How later papers used it
145 later papers cite it
16 later papers by other authors are listed below: 13 used its method or tool and 3 used its data or values.
Uses its method or tool 13 of 45 papers with this label
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Worked in rainbow-ladder truncation of QCD using the Maris-Tandy model of the quark-gluon interaction.
Hadronic contribution to the muon g-2: a Dyson-Schwinger perspective (2011) · 1.00 · paraphrased: the licence does not allow quoting
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Replaced the combination of the strong coupling and gluon propagator with the Maris-Tandy interaction, setting its free parameter to omega = 0.4 GeV.
Vector mesons as dynamical resonances in the Bethe-Salpeter framework (2018) · 0.93 · paraphrased: the licence does not allow quoting
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Adopted the Maris-Tandy model, in which the gluon propagator is written as a sum of an infrared term and a UV term.
Quark propagator with complex-valued momentum from Schwinger-Dyson equation in the Euclidean space (2024) · 0.95 · paraphrased: the licence does not allow quoting
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Used the model proposed by Maris and Tandy as the effective interaction, with parameter omega = 0.4 and light quarks.
Properties of quarks and mesons in the Dyson-Schwinger/Bethe-Salpeter approach (2011) · 0.94 · paraphrased: the licence does not allow quoting
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Used the parameterization of this paper as the effective interaction, with omega an effective inverse range and D an overall strength of the first term.
Masses of J^PC =1^-+ exotic quarkonia in a Bethe-Salpeter-equation approach (2015) · 0.84 · paraphrased: the licence does not allow quoting
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Implemented the interaction of Maris and Tandy in its study.
Hadron properties from QCD bound-state equations (2009) · 0.99 · paraphrased: the licence does not allow quoting
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Adopted the ansatz for the effective coupling introduced in this paper.
Delta and Omega masses in a three-quark covariant Faddeev approach (2011) · 0.98 · paraphrased: the licence does not allow quoting
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Chose its effective interaction from this paper in rainbow-ladder truncation.
Hadronic decays of mesons and baryons in the Dyson-Schwinger approach (2011) · 0.82 · paraphrased: the licence does not allow quoting
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Relied on the model proposed in this paper, in which the infrared enhancement of the effective strong coupling is accomplished without a singular but integrable delta function.
Instantaneous Bethe-Salpeter View of Goldstone-Type Pseudoscalar Mesons (2016) · 0.98 · paraphrased: the licence does not allow quoting
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Left the parameters of its interaction unchanged from this paper.
Spectra of heavy quarkonia in a Bethe-Salpeter-equation approach (2014) · 0.96 · paraphrased: the licence does not allow quoting
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Used the Maris-Tandy model for the effective coupling, Eq. (10) of this paper, with parameters Lambda = 0.74 GeV and eta = 1.85 +/- 0.2.
Single pseudoscalar meson pole and pion box contributions to the anomalous magnetic moment of the muon (2019) · 0.85 · paraphrased: the licence does not allow quoting
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Specified its scalar function in Euclidean space by the Maris-Tandy model.
Pion Electromagnetic Form Factor from Bethe-Salpeter Amplitudes with Appropriate Kinematics (2024) · 0.85 · paraphrased: the licence does not allow quoting
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Took the rainbow-ladder truncation and aligned the quark's Dyson-Schwinger equation and the meson's Bethe-Salpeter equation.
The light front wave functions and diffractive electroproduction of vector mesons (2021) · 0.96 · paraphrased: the licence does not allow quoting
Uses its data or values 3 of 9 papers with this label
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Extracted its inversion input from a chiral-limit model solution of this paper to the QCD equation of motion for the full quark propagator.
Instantaneous Bethe-Salpeter Look at the Lightest Pseudoscalar Mesons (2017) · 0.90 · paraphrased: the licence does not allow quoting
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Adopted the values D0 = 9.3 x 10^5 MeV^2 and sigma = 400 MeV from this paper.
The chiral phase transition with a chiral chemical potential in the framework of Dyson-Schwinger equations (2015) · 0.99 · paraphrased: the licence does not allow quoting
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Took the quark mass and wave-function renormalization functions from a solution of this paper.
Light Pseudoscalar Mesons: an Inverse Instantaneous Bethe-Salpeter Glimpse (2017) · 0.90 · paraphrased: the licence does not allow quoting
How the literature uses it
102 arXiv papers cite this in 178 sentences
Papers citing it · 111 sentences without a confident label
Builds on it 1 paper
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Together with the isovector ground state pseudoscalars [ref] , first excited pseudoscalar states [ref] and ground state vectors [ref] , this is a new case among the few where the Euclidian Bethe Salpeter equation has been solved so far.
Microscopic quark study of the eta and eta' masses · Conclusion · 0.89
Uses its method or tool 28 papers
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The standard DSE-RL interaction kernel [ref] that generates quark propagators and BSE vertices and meson bound states is where [equation] Here $α̃_s(q^2)$ denotes a continuation of the 1-loop $α_s(q^2)$ to provide smooth non-singular coverage for the entire domain of $q^2$.
Gluon PDF from Quark dressing in the Nucleon and Pion · Introduction · 0.85
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We work in rainbow-ladder truncation of QCD using the Maris-Tandy model of the quark-gluon interaction [ref] .
Hadronic contribution to the muon g-2: a Dyson-Schwinger perspective · Calculational scheme · 1.00
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where, $C_F=4/3$ is the color factor and $q=k-p$ the momentum of the gluon propagator $D^μν(q)$ ; in this study the combination $g_s^2 D^μν(q)$ is replaced by the Maris-Tandy interaction [ref] , with its free parameter set to $ω=0.4$ GeV.
Vector mesons as dynamical resonances in the Bethe-Salpeter framework · Introduction · 0.93
Uses its data or values 10 papers
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We extract our inversion input from a popular chiral-limit model solution [ref] to the QCD equation of motion for the full quark propagator.
Instantaneous Bethe-Salpeter Look at the Lightest Pseudoscalar Mesons · Inversion: Confining Interquark Potential Compatible with Goldstone's Theorem · 0.90
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Owing to Poincaré covariance, just two Lorentz-scalar functions characterize the propagator of a quark (of four-momentum $p$), its mass $M(p^2)$ and its wave-function renormalization $Z(p^2)$, which we take from a solution [ref] of this quark propagator's Euclidean-space equation of motion (Fig. [ref]).
Light Pseudoscalar Mesons: an Inverse Instantaneous Bethe-Salpeter Glimpse · Introduction · 0.90
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Hereafter we will fix the latter to $Λ=0.72$ GeV which has been used in [ref] to reproduce experimental results for meson and baryon properties.
On baryon properties from a covariant Faddeev approach · Rainbow-ladder truncation · 0.84
Compares with it 2 papers
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The results of our calculation in the $3$PI effective action at 3-loop ($3$PI-3L) are detailed in Table [ref] and contrasted with typical results from rainbow-ladder (RL) [ref] , a recent study of mesons (and baryons) in the framework of the $2$PI effective action at 3-loop ($2$PI-3L) [ref] , and of course their experimentally known values from the PDG [ref] .
Light mesons in QCD and unquenching effects from the 3PI effective action · Application to bound-states · 1.00
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In the case of Maris-Tandy, the resultant rho mass of $∼720$ MeV is similar to that obtained in other studies with this interaction [ref] .
Beyond the rainbow: effects from pion back-coupling · Results · 1.00
Cites it as support 1 paper
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Studies using this parametrization have demonstrated that pseudoscalar and vector-meson ground state properties are insensitive to a variation of the coupling width $ω$ in a certain range [ref] , i.e. independent of the detailed shape of the interaction in the infrared.
Hadron properties from QCD bound-state equations · Effective quark-gluon interaction · 0.97
Cites it as background 17 papers
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The analytic properties of the quark DSE that arises when only the infrared (IR) part of the Maris-Tandy interaction [ref] is taken into account has been the subject of a thorough study [ref] .
The analytic properties of the quark propagator from an effective infrared interaction model · Introduction · 0.85
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The calculation of observables from the Bethe–Salpter amplitudes, such as leptonic decay constants for the pseudoscalar and vector mesons [ref] , requires that they are properly normalised.
Bethe-Salpeter studies of mesons beyond rainbow-ladder · Decay constants and normalisation · 0.83
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There are more realistic models such as the Maris-Tandy model [ref] in which the interaction vanishes at infrared, and Qin-Chang (QC) model [ref] , whose interaction remains a constant value at infrared.
Dyson-Schwinger equations towards cold-dense QCD matter with improved truncations · Introduction · 0.96
Discussion
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