REVIEW
Confining Solution of the Dyson-Schwinger Equations in Coulomb Gauge
High Energy Physics - Theory · Submitted 21 Dec 2006 · 13 references
Pith's verdict: A competent numerical companion to the authors' own infrared analysis: it finds the β=1 branch in a full momentum-space solve and gets a linear Coulomb potential, but the exponent extraction has no stability analysis and the potential is algebraically the same statement, not a second result.
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Referee report
The paper
The paper claims
The Coulomb-gauge equations of Yang-Mills theory admit a second, confining solution whose static quark potential rises strictly linearly.
The reading
What carries the argument
Three ingredients carry the argument. First, the horizon condition $d^{-1}(mu=0)=0$, imported from Zwanziger, forces the ghost exponent $beta$ positive and is what makes the gluon energy infrared divergent. Second, the sum rule $2beta = alpha + 1$, which follows from the non-renormalization of the ghost-gluon vertex, ties the gluon exponent $alpha$ to the ghost exponent $beta$; combined with the gap equation's infrared limit $lim_{kto 0}(omega(k)-chi(k)) = c$, it is what allows $beta_2=1$ to produce a strictly linear potential rather than a merely rising one. Third, the numerical scheme: Chebyshev expansion on a logarithmic momentum grid, double-logarithmic representation for divergent functions, analytic power-law and logarithmic asymptotics used as fit forms whose exponents and coefficients are still determined by nonlinear least squares, Gauss-Legendre quadrature after a logarithmic change of radial variable, and relaxed iteration with $r approx 0.1$. The design point is that the asymptotics are used as fitting templates, not imposed, so the numerically extracted exponents serve as a check on the analytic predictions.
Extended reading notes
Core claim
The central claim is that the one-loop Dyson-Schwinger equations of the Hamiltonian (variational) approach to Yang-Mills theory in Coulomb gauge possess a second numerical solution, with infrared exponent $beta_2 = 1$, in addition to the previously found $beta_1 approx 0.796$. The authors solve the coupled equations for the ghost form factor $d(k)$, the gluon energy $omega(k)$ and the scalar curvature $chi(k)$ over the whole momentum range, imposing the horizon condition $d^{-1}(0)=0$ and the renormalization choices $bar{chi}(1)=0$, $c=0$, with $bar{omega}(1)$ left as a free parameter (their displayed solution uses $bar{omega}(1)=1.6$). In the infrared, $omega$ and $chi$ are found to share the same divergent power law, consistent with the analytic expectation, and $omega(k)-chi(k)$ tends to a constant. Feeding the solution into the Coulomb term of the Hamiltonian for two static colour charges gives a potential that is linear in $r$ to within an estimated error under one percent, and the ghost-gluon running coupling $alpha(k) = frac{2}{3pi},k,d^2(k),omega^{-1}(k)$ is monotonic with an infrared fixed point matching the analytically predicted $alpha(0) = 16pi/(3N_c)$.
Load-bearing premise
The horizon condition $d^{-1}(0)=0$ is imposed as an input from outside rather than derived from the variational principle, and without it the ghost propagator is not enhanced, the exponent is not forced positive, and the confining solution does not follow.
Editorial extensions
If this is right
- The variational Hamiltonian approach in Coulomb gauge reproduces a linearly rising static quark potential from its own gap equations, so confinement need not be added as an external assumption about the infrared behaviour of the propagators.
- The ghost-gluon running coupling has a finite infrared limit $alpha(0)=16pi/(3N_c)$, so the coupling does not diverge in the infrared in this scheme, which constrains how the beta function can behave at low momentum.
- The Coulomb string tension extracted from the linear fit can be compared with lattice determinations, which the authors note are a factor of roughly 1.5 to 3 larger than the Wilson-loop string tension, in line with the analytic statement that the Coulomb tension is an upper bound.
- Because the infrared exponents and ultraviolet behaviour are reported to be insensitive to the remaining renormalization constants once the horizon condition is adopted, the qualitative confining picture is claimed to be robust against those choices, with changes confined to intermediate momenta.
Reading between the lines
- If the $beta=1$ branch is a genuine feature of the untruncated equations rather than of the one-loop truncation and the fitted asymptotic templates, then the earlier numerical search that found only $beta approx 0.796$ was limited by its discretization and not by the physics; a convergence study in grid density and fit range would settle which it is.
- The reported insensitivity to $bar{omega}(1)$ suggests a one-parameter family of confining solutions; whether the Coulomb string tension varies across that family is a concrete question the paper's own figures could answer but does not quantify.
- The linearity claim is a statement about the Coulomb potential alone, so it is testable against lattice Coulomb-gauge measurements of the same quantity at intermediate separations, where the variational truncation is least controlled.
- Since the horizon condition is what drives the whole chain, a useful extension would be to solve the same truncated system with $d^{-1}(0)$ held at small nonzero values and watch the exponent and the potential's slope move, turning an input assumption into a dial.
Original abstract
The Dyson-Schwinger equations arising from minimizing the vacuum energy density in the Hamiltonian approach to Yang-Mills theory in Coulomb gauge are solved numerically. A new solution is presented which gives rise to a strictly linearly rising static quark potential and whose existence was previously observed in the infrared analysis of the Dyson-Schwinger equations. For the new solution we also present the static quark potential and calculate the running coupling constant from the ghost-gluon vertex.
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 Dyson-Schwinger equations arising from minimizing the vacuum energy density in the Hamiltonian approach to Yang-Mills theory in Coulomb gauge are solved numerically. A new solution is presented which gives rise to a strictly linearly rising static quark potential and whose existence was previously observed in the infrared analysis of the Dyson-Schwinger equations. For the new solution we also present the static quark potential and calculate the running coupling constant from the ghost-gluon vertex.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | The Dyson-Schwinger equations arising from minimizing the vacuum energy density in the Hamiltonian approach to Yang-Mills theory in Coulomb gauge are solved numerically. | method 0.82 | 0.92 | 0.08 | asserted 1.00 |
| s1 | A new solution is presented which gives rise to a strictly linearly rising static quark potential and whose existence was previously observed in the infrared analysis of the Dyson-Schwinger equations. | result 0.72 | 0.74 | 0.75 | asserted 1.00 |
| s2 | For the new solution we also present the static quark potential and calculate the running coupling constant from the ghost-gluon vertex. | contribution 0.51 | 0.94 | 0.15 | asserted 1.00 |
What was examined, and what was not
- arXiv listing abstract v2
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- P abstract
- S sections
- T body sentences
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- R cross-paper relations
Figures
Figures reproduced from arXiv:hep-th/0612241 by the authors.
References
How later papers used it
49 later papers cite it
2 papers by the same authors are listed below: 2 used its data or values.
Uses its data or values 2 of 5 papers with this label · 2 by the same authors
By the same authors
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Replaced the running coupling, which this paper calculated from the ghost-gluon vertex, by its infrared value.
Quark Sector of the QCD Groundstate in Coulomb Gauge (2013) (same authors) · 0.87 · paraphrased: the licence does not allow quoting
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Noted that the ghost form factor this paper obtained for the alpha=1 solution can be fitted by another work's form.
Vertex functions of Coulomb gauge Yang--Mills theory (2014) (same authors) · 0.92 · paraphrased: the licence does not allow quoting
How the literature uses it
47 arXiv papers cite this in 121 sentences
Papers citing it · 79 sentences without a confident label
Builds on it 2 papers
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In Ref. [ref] the variational Hamiltonian approach to Yang–Mills theory in Coulomb gauge [ref] was extended to full QCD by including the quark-gluon coupling explicitly in the vacuum wave functional.
Variational and Dyson--Schwinger Equations of Hamiltonian Quantum Chromodynamics · Introduction · 0.83
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The unperturbed basis constructed from the eigenstates of the unperturbed Hamiltonian, which up to the colour index of the gauge field coincides with the Hamiltonian for QED (without fermions), was generalized to multiple quasi-gluon states on top of the non-perturbative vacuum wave functional used in the variational approach [ref] .
Perturbation theory in the Hamiltonian approach to Yang-Mills theory in Coulomb gauge · Summary and Conclusions · 0.84
Uses its method or tool 3 papers
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[ref] and [ref] .
The Yang-Mills Vacuum in Coulomb Gauge in D=2+1 Dimensions · Numerical results · 0.91
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In the variational approach developed in Refs. [ref] one attempts to solve the functional Schrödinger equation [equation] for the QCD vacuum state $|⟩$ by means of the variational principle with suitable trial Ansätze for the vacuum wave functional $[A]=⟨A|⟩$.
Dynamical Quark Mass Generation in QCD\textsubscript{3} within the Hamiltonian approach in Coulomb gauge · Vacuum wave functional and quark propagator · 0.86
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Technically, the system is solved in the same way as described in [ref] , except for the following differences.
Subcritical solution of the Yang-Mills Schroedinger equation in the Coulomb gauge · Full subcritical solutions · 0.98
Uses its data or values 5 papers
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(Within our approximation, this is the only place where the actual form of the vacuum wave functional enters.) The exact analytical expressions are unknown, but we have reliable data from recent variational calculations [ref] , which are also in decent agreement with high precision lattice measurements [ref] .
On the temporal Wilson loop in the Hamiltonian approach in Coulomb gauge · Yang-Mills theory in $(3+1)$ dimensions · 0.94
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Fig. 1 shows the result for the dielectric function ([ref]) obtained from the solutions to the Dyson-Schwinger equations reported in [ref] .
Dielectric function of the QCD vacuum · The dielectric function · 0.91
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All numerical plots displayed in this section were calculated by D.Epple [ref] .
Nonperturbative aspects of Yang-Mills theory · Full numerical solutions · 0.85
Compares with it 2 papers
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In the momentum regime where reliable lattice data are available, there is a reasonable agreement between lattice data [ref] , [ref] and the continuum results [ref] , [ref] , [ref] .
Dielectric function of the QCD vacuum · The dielectric function · 0.92
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We can compare these results with the solutions of DSEs obtained in the variational approach in Refs. [ref] .
Color Coulomb Potential in Yang-Mills Theory from Hamiltonian Flows · Introduction · 1.00
Cites it as support 4 papers
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Solutions of the Dyson-Schwinger equations for the three-gluon and four-gluon couplings [ref] and phenomenological studies [ref] of QCD couplings based on physical observables such as $τ$ decay [ref] and the Bjorken sum rule [ref] , show that the QCD $β$ function vanishes and $α_s(Q^2)$ become constant at small virtuality; i.e., effective charges develop an “infrared fixed point." Recent lattice simulations [ref] and nonperturbative analyses [ref] have also indicated an infrared fixed point for QCD.
AdS/CFT and Light-Front QCD · Introduction · 1.00
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Our variational approach has given a quite decent description of the infrared sector of Yang-Mills theory as, for example, a linearly rising non-Abelian Coulomb potential [ref] , an infrared diverging gluon energy (expressing confinement) [ref] in accord with lattice data [ref] , an infrared finite running coupling constant [ref] , a perimeter law for the 't Hooft loop [ref] , an area law for the Wilson loop [ref] and a dielectric function of the Yang-Mills vacuum in accord with the bag model picture [ref] .
Quark Sector of the QCD Groundstate in Coulomb Gauge · Introduction · 0.97
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It is precisely this picture which is supported by the variational calculation in the Hamiltonian approach to Yang-Mills theory in Coulomb gauge developed in Refs. [ref] .
A covariant variational approach to Yang-Mills Theory · Gaussian trial measure · 1.00
Cites it as background 21 papers
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Recently progress has been made in variationally solving the Yang-Mills Schrödinger equation in Coulomb gauge [ref] .
The 't Hooft loop in the Hamiltonian approach to Yang-Mills theory in Coulomb gauge · Introduction · 0.82
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The Coulomb form factor $f(k)$ measures the ratio of the vev of its square to the square of vevs, [equation] Finally we also consider the expectation value of the curvature [ref] defined by [equation] The DS equations for these correlations functions were independently studied in [ref] and [ref] under different approximation schemes.
Subcritical solution of the Yang-Mills Schroedinger equation in the Coulomb gauge · Variational Coulomb QCD · 0.96
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Recently, there has been much activity in the Hamiltonian approach to Yang–Mills theory in Coulomb gauge [ref] .
Perturbation theory in the Hamiltonian approach to Yang-Mills theory in Coulomb gauge · Introduction · 0.91
Discussion
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