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A Precise Determination of the Running Coupling in the SU(3) Yang-Mills Theory

High Energy Physics - Lattice · Submitted 13 Sep 1993

Pith's verdict: The SU(3) step-scaling paper: the method works and the continuum extrapolation is clean, but the headline alpha_MS precision is capped by a matching coefficient nobody has computed yet, not by the data.

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arXiv IDhep-lat/9309005 (version 1)
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CitationMartin Luescher, Peter Weisz, Rainer Sommer, Ulli Wolff. "A Precise Determination of the Running Coupling in the SU(3) Yang-Mills Theory." arXiv:hep-lat/9309005 (1993). https://pith.science/paper/3GS5UPWL
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Referee report
The paper

The paper claims

By recursively doubling and tripling the box size on the lattice, the authors follow the SU(3) Yang–Mills coupling across a factor of 24 in energy and find it settles onto the perturbative prediction, fixing $α_{MS}(q)=0.1108(23)(10)$ at $q

The reading

The paper asks a question that sounds circular but is not: if you fix the parameters of a non-Abelian gauge theory at low energy, can you actually compute what the coupling becomes at high energy, where perturbation theory takes over? Doing so requires bridging a large span of scales without ever leaving the regime where the lattice simulation is controlled. The authors do it by shrinking and growing a finite box: the running coupling is defined at the box size $L$, and the change in the coupling when $L$ is multiplied by 2 (or, at the last step, by 3/2) is measured at fixed bare coupling. Chaining these steps together walks the coupling from $g^2 = 3.48$ down to $1.243$, a factor of about 24 in scale, and the resulting curve agrees with the two-loop renormalization-group prediction to within statistical errors. The payoff is a value of the coupling in the $MS$-bar scheme of dimensional regularization, $α_{MS}(q) = 0.1108(23)(10)$ at $q = 37 r_0^{-1}$ (roughly 14 GeV if $r_0 = 0.5$ fm), with a stated total error of a few percent. The authors are careful that the second error, of order $α^3$, only estimates the size of the unknown two-loop matching correction.

What carries the argument

The step scaling function $Σ(s,u)$ is the object that carries the argument: it is the integrated form of the Callan–Symanzik $β$-function, telling you what happens to the coupling when the box is scaled by $s$. Because it is defined at fixed bare coupling on pairs of lattices of size $L$ and $sL$, it can be computed by simulation and then extrapolated to the continuum with an ansatz $Σ(s,u,a/L) = Σ(s,u)(1 + δ(s,u)a/L)$, without ever needing to know the lattice spacing in physical units. The coupling itself comes from differentiating the Schrödinger functional $Z$ with respect to a one-parameter family of constant Abelian boundary fields, $∂_η ln Z|_{η=0} = k/ḡ^2$, with the normalization $k$ chosen so that $ḡ^2 = g_0^2$ at lowest order; a one-loop improved action with boundary coefficient $c_t = 1 - 0.08900(5)g_0^2$ removes cutoff effects through order $a$. The second ingredient is the scale conversion: the ratio $L_{max}/r_0$, where $r_0$ is the distance at which $r^2F(r) = 1.65$, ties the dimensionless evolution to the low-energy dynamics.

Extended reading notes

Core claim

The central claim is that the running coupling of SU(3) Yang–Mills theory, defined non-perturbatively through the Schrödinger functional on a box of size $L$, evolves according to perturbation theory once the coupling is small enough, and that this evolution can be computed with controlled errors. Concretely, the authors measure the step scaling function $Σ(s,u)$ — the coupling at box size $sL$ given the coupling $u$ at size $L$ — for $s=2$ at four values of $u$ and for $s=3/2$ at the largest coupling, extrapolate each to the continuum limit $a/L → 0$, and then integrate the resulting curve. The lattice data show no statistically significant cutoff dependence, and the integrated evolution matches the two-loop $β$-function essentially point by point; only at the largest couplings is a small deviation visible, which a correlated fit absorbs into an effective three-loop coefficient $b^{eff}_2 = 1.5(8)/(4π)^3$, about twice the known three-loop value in minimal subtraction. Converting to physical units through $L_{max}/r_0 = 0.674(50)$ and the one-loop matching relation $α_{MS} = α + 1.25563(4)α^2 + …$ gives $α_{MS}(q) = 0.1108(23)(10)$ at $q = 37 r_0^{-1}$.

Load-bearing premise

The chain from a dimensionless lattice coupling to a physical number hangs on the conversion factor $L_{max}/r_0 = 0.674(50)$, obtained by linearly extrapolating the static quark force from only four data points of other groups' large-volume simulations, and the authors themselves call the errors large at this step.

Editorial extensions

If this is right

  • The perturbative scaling regime and the low-energy domain of SU(3) Yang–Mills are smoothly connected, with no intermediate regime where the coupling behaves in a way perturbation theory cannot describe.
  • A numerical value of $α_{MS}$ at a specified momentum is available from first principles alone, with the dominant uncertainty traceable to the scale-setting ratio $L_{max}/r_0$ rather than to the coupling evolution.
  • Setting $r_0 = 0.5$ fm gives $L_{max} = 0.337(25)$ fm and $\sqrt{K} = 481(32)$ MeV, a string tension somewhat larger than values extracted from phenomenological heavy-quark potentials fitted to charmonium.
  • Within errors, $2α_{MS}|_{SU(2)} = 3α_{MS}|_{SU(3)}$ when momenta are measured in units of $r_0$, suggesting that $Nα_{MS}$ depends only weakly on the number of colours.
  • The comparison with the improved one-loop bare-coupling formula of Parisi–Lepage–Mackenzie agrees at the few-percent level over the range of bare couplings examined, so the two routes to $α_{MS}$ are consistent where they overlap.

Reading between the lines

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

  • The error budget is lopsided: the evolution itself is under control, while the conversion factor $L_{max}/r_0 = 0.674(50)$ carries a 7 percent uncertainty built from only four data points, one of them an unpublished private communication. A dedicated high-statistics static-force calculation at an intermediate coupling such as $β = 6.8$ would buy more precision than any amount of additional step-sc
  • Because the same technique with the same scale-setting reproduces the SU(2) result, the natural next check is SU(4) or the large-$N$ limit: if $Nα_{MS}$ is genuinely flat in $N$ at fixed $q r_0$, that is a sharp, cheap test of large-$N$ scaling that does not require new analytic input.
  • The fitted effective three-loop coefficient $b^{eff}_2 \approx 1.5/(4π)^3$ is a concrete target for perturbation theory: a three-loop computation of the $β$-function for this particular finite-volume coupling would either reproduce that number or expose the fit as absorbing genuine non-perturbative curvature. Either outcome sharpens the matching formula's error estimate, which currently rests on a
Original abstract

A non-perturbative finite-size scaling technique is used to study the evolution of the running coupling (in a certain adapted scheme) in the SU(3) Yang-Mills theory. At low energies contact is made with the fundamental dynamical scales, such as the string tension K, while at larger energies the coupling is shown to evolve according to perturbation theory. In that regime the coupling in the MS-bar scheme of dimensional regularization is obtained with an estimated total error of a few percent.

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-1.13-20260917 via OpenRouter, question bank abstract-p1-20260923, 2026-09-23: 1 request, 2,977 input tokens, $0.0001 reported.

What the abstract itself states, as probabilities: claims first 0.03 · states limitation 0.39 · human participants 0.01 · controlled comparison 0.03 · randomized assignment 0.01 · states quantitative result 0.66 · compares with prior results 0.17 · mentions code or data availability 0.02.

The abstract, sentence by sentence

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

A non-perturbative finite-size scaling technique is used to study the evolution of the running coupling (in a certain adapted scheme) in the SU(3) Yang-Mills theory. At low energies contact is made with the fundamental dynamical scales, such as the string tension K, while at larger energies the coupling is shown to evolve according to perturbation theory. In that regime the coupling in the MS-bar scheme of dimensional regularization is obtained with an estimated total error of a few percent.

background contribution method result interpretation main claim

What the classifier reports for each sentence. The number is the probability it gave the label.
#sentencerolethe authors' own workstates the main conclusionstrength
s0 A non-perturbative finite-size scaling technique is used to study the evolution of the running coupling (in a certain adapted scheme) in the SU(3) Yang-Mills theory. method 0.77 0.91 0.10 asserted 0.99
s1 At low energies contact is made with the fundamental dynamical scales, such as the string tension K, while at larger energies the coupling is shown to evolve according to perturbation theory. result 0.94 0.87 0.31 asserted 1.00
s2 In that regime the coupling in the MS-bar scheme of dimensional regularization is obtained with an estimated total error of a few percent. result 1.00 0.91 0.42 asserted 0.99

What kind of paper the classifier reports this is: simulation study 0.95 · evidence from simulation or computation 1.00.

What was examined, and what was not

sources read
  • arXiv listing abstract v1
not examined
  • full text
  • figures and tables
  • references and citing sentences
  • relations to other papers
levels run
  • P abstract
not run
  • S sections
  • T body sentences
  • C citations
  • R cross-paper relations

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 2. Extrapolation of the lattice step scaling function to the con￾tinuum limit. The points at a=L = 0 represent the extrapolated values. perturbative improvement of the action. Further studies are however needed to completely clarify the issue. We now proceed to discuss the cuto dependence of v, or, more precisely, of the function (g2 ; a=L) [eq.(3.27)]. The data listed in the last two columns of table 2 show that v is hardly changing as a=L is made smaller at xed g2 . Note that in most cases we have results for a=L from 0:2 down to 0:05 (small variations of g2 can here be ignor
Figure 3. Plot of v = !(g 2 ). The dashed line is a t, using eq.(5.6) with an adjustable 2-loop coecient, to all data points except the one at the largest coupling. and the running coupling in our scheme may very well turn out to be an exceptional case. 5.3 Physical units We now need to relate Lmax to the dynamical low-energy scales of the theory in in nite volume. As discussed in sect. 1, we decided to take the distance r0 as the basic reference scale. Our rst goal is thus to compute the conversion factor Lmax=r0. The heavy quark force F (r) has previously been calculated through nu￾m
Figure 5. Comparison of numerically computed values of the running coupling (data points) with perturbation theory. The full line represents the t described in subsect. 5.2, while the dashed (dotted) curve is obtained by integrating eq.(3.21), starting at the right-most point and using the 2- loop (1-loop) {function. the coupling. 21

Showing 3 of the paper's 5 figures. See all figures in the PDF ↗ Figures reproduced from arXiv:hep-lat/9309005 by the authors.

References
How later papers used it

69 later papers cite it

Evidence: substantial. 61 of the citing papers share no author with it, and 30 of those carry a confident label from Pith's citation classifier.

Pith read 14 of the 147 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

Uses its method or tool 3 of 24 papers with this label
Uses its data or values 1 of 4 papers with this label
Compares with it 1 of 10 papers with this label
How the literature uses it

68 arXiv papers cite this in 146 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 · 80 sentences without a confident label

Builds on it 2 papers
Uses its method or tool 24 papers
Uses its data or values 4 papers
Compares with it 10 papers
Cites it as background 13 papers

Discussion

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