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The running coupling from the QCD Schr\"odinger functional -- a one-loop analysis

High Energy Physics - Lattice · Submitted 9 Aug 1995

Pith's verdict: The paper that puts quarks into the Schrödinger functional coupling and hands you the one-loop matching to MSbar plus the boundary improvement coefficient — the numbers hold up.

T0 · AI review

How this review was made: An AI referee (selfhosted/deepseek-v4.1-flash) read the paper on November 11, 2026 and answered a fixed list of questions about it. T0 is the starting level every paper gets. The levels describe how deeply Pith has checked the paper, never the authors.

  1. T0 AI review An AI read the paper and answered a fixed list of questions.
  2. T1 Audit Automatic checks that the references and files the paper relies on exist and match.
  3. T2 Compute The paper's code or calculations re-run with the same results.
  4. T3 Formal statement The claims written out in a formal math language a computer can read.
  5. T4 Proof Those claims proved, and the proof checked by computer.

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arXiv IDhep-lat/9508012 (version 1)
Pith IDZZXTOQUL, Pith's permanent record of this paper and its review
CitationRainer Sommer, Stefan Sint. "The running coupling from the QCD Schr\"odinger functional -- a one-loop analysis." arXiv:hep-lat/9508012 (1995). https://pith.science/paper/ZZXTOQUL
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Referee report
The paper

The paper claims

A finite-volume definition of the running QCD coupling with quarks is matched to MSbar at one loop, and the boundary improvement coefficient needed for controlled continuum extrapolations is computed.

The reading

The paper's goal is to make the strong coupling computable from first principles on a lattice when quarks are present, not just in the pure-gauge theory. The authors define a running coupling in a finite box by measuring how the QCD effective action responds to a change in a color-electric boundary field; the box size $L$ sets the renormalization scale. They choose quark boundary conditions that are periodic up to a phase $theta$, finding that $theta=pi/5$ gives a larger lowest Dirac eigenvalue than $theta=0$. At one loop they compute the conversion factor to the $bar{mathrm{MS}}$ scheme, the quark-mass dependence of the $beta$-function, and the $O(a)$ boundary improvement coefficient. If this is right, Monte Carlo measurements of the finite-volume coupling can be converted to $alpha_{bar{mathrm{MS}}}$ with a controlled perturbative error and the main lattice artefacts can be removed or shown to be small; the authors note that the complete $O(a)$-improved action for the Schroedinger functional is not yet known beyond this one-loop, single-observable analysis.

What carries the argument

The load-bearing object is the Schroedinger functional effective action $Gamma[B]$ on a space-time cylinder whose spatial boundary values are fixed color-electric gauge fields. The running coupling is defined by differentiating $Gamma$ with respect to a parameter $eta$ that scales the boundary field, normalized by the classical action so that the coupling equals the bare coupling at tree level. Quark fields are periodic up to a phase $theta$; the choice $theta=pi/5$ is made because the massless Dirac operator in the classical background then has a larger lowest eigenvalue, which improves the condition number of the fermion matrix. The quark determinant is evaluated by a first-order recursion in each fixed spatial-momentum and color sector, and the continuum matching is extracted from the asymptotic $1/l$ expansion of the lattice coefficient. The integrated $beta$-function is packaged in the step scaling function $Sigma(s;u,z)$, which is the quantity a non-perturbative simulation would measure.

Extended reading notes

Core claim

The central claim is that the Schroedinger functional gives a non-perturbative definition of a running coupling in QCD with quarks, and that its one-loop relation to the $bar{mathrm{MS}}$ scheme is under control. For massless quarks the quark contribution to the matching coefficient is $c_{1,1}(0)=0.039863(2)$ for $theta=pi/5$ and $0.022504(2)$ for $theta=0$, both small and positive. The quark-mass dependence is parametrized by Chebyshev fits for $z=mL$ below about 10 and by a $ln z$ plus power-correction form for large $z$; the resulting threshold behaviour in the one-loop $beta$-function is broad rather than sharp. The paper also computes the boundary improvement coefficient $c_t^{(1,1)}=0.0191410(1)$ needed to cancel the $O(a)$ artefacts from the time boundaries. For the step scaling function, one massless flavour induces only sub-percent artefacts with the standard action, and these fall roughly like $(a/L)^2$ once the clover term and the boundary improvement are switched on.

Load-bearing premise

The one-loop continuum matching coefficient is extracted from a lattice series assumed to have the asymptotic form $p_{1,1}$ approaching $r_0+s_0ln l+(r_1+s_1ln l)/l$, with $s_0$ fixed to its exact value and only the first $1/l$ corrections retained; if that truncation or the numerical $1/l$ extrapolation is inadequate, the quoted $c_{1,1}$ values shift.

Editorial extensions

If this is right

  • Monte Carlo measurements of the finite-volume Schroedinger-functional coupling can be converted to $alpha_{bar{mathrm{MS}}}$ with a one-loop conversion factor.
  • Heavy quarks with $z=mL$ above about 2 can be omitted from the one-loop $beta$-function evolution with an error of about $0.003$ in $g^{-2}$, below the precision of the pure-gauge step-scaling result.
  • The boundary coefficient $c_t^{(1,1)}$ can be tuned to remove the linear-in-$a$ artefacts from the step scaling function at one loop.
  • With the clover term, lattice artefacts in the step scaling function fall roughly like $(a/L)^2$; without it they can look almost constant over the lattice sizes accessible to simulations.
  • The construction extends recursive finite-size scaling to QCD with dynamical quarks, which is the step needed for a first-principles determination of the strong coupling.

Reading between the lines

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

  • The $theta=pi/5$ choice is justified by the free Dirac spectrum; a direct Monte Carlo measurement of the low-lying spectrum at realistic coupling would test whether the gain survives gauge fluctuations.
  • Because the matching coefficients are small, the Schroedinger-functional coupling may be numerically close to $bar{mathrm{MS}}$ at accessible scales; whether that closeness persists at two loops is an open calculation.
  • The broad threshold behaviour and the $1/z$ tail suggest that omitting a heavy flavour is safe at the quoted precision, but a precision extraction near a flavour threshold may need the full mass dependence.
  • The improvement coefficient is computed at one loop; non-perturbative tuning at stronger coupling may be needed before continuum extrapolations of dynamical simulations are fully controlled.
Original abstract

Starting from the Schr\"odinger functional, we give a non-perturbative definition of the running coupling constant in QCD. The spatial boundary conditions for the quark fields are chosen such that the massless Dirac operator in the classical background field has a large smallest eigenvalue. At one-loop order of perturbation theory, we determine the matching coefficient to the $\MSbar$-scheme and discuss the quark mass effects in the $\beta$-function. To this order, we also compute the Symanzik improvement coefficient necessary to remove the $\Oa$ lattice artefacts originating from the boundaries. For reasonable lattice resolutions and the standard Wilson action, lattice artefacts are found to be only weakly dependent on the lattice spacing $a$, while they vanish quickly with the improved action of Sheikholeslami and Wohlert.

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, 4,328 input tokens, $0.0002 reported.

What the abstract itself states, as probabilities: claims first 0.04 · states limitation 0.43 · human participants 0.01 · controlled comparison 0.09 · randomized assignment 0.01 · states quantitative result 0.11 · compares with prior results 0.37 · mentions code or data availability 0.02.

The abstract, sentence by sentence

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

Starting from the Schr\"odinger functional, we give a non-perturbative definition of the running coupling constant in QCD. The spatial boundary conditions for the quark fields are chosen such that the massless Dirac operator in the classical background field has a large smallest eigenvalue. At one-loop order of perturbation theory, we determine the matching coefficient to the $\MSbar$-scheme and discuss the quark mass effects in the $\beta$-function. To this order, we also compute the Symanzik improvement coefficient necessary to remove the $\Oa$ lattice artefacts originating from the boundaries. For reasonable lattice resolutions and the standard Wilson action, lattice artefacts are found to be only weakly dependent on the lattice spacing $a$, while they vanish quickly with the improved action of Sheikholeslami and Wohlert.

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 Starting from the Schr\"odinger functional, we give a non-perturbative definition of the running coupling constant in QCD. contribution 0.99 0.93 0.34 asserted 1.00
s1 The spatial boundary conditions for the quark fields are chosen such that the massless Dirac operator in the classical background field has a large smallest eigenvalue. method 0.98 0.84 0.03 asserted 0.99
s2 At one-loop order of perturbation theory, we determine the matching coefficient to the $\MSbar$-scheme and discuss the quark mass effects in the $\beta$-function. contribution 0.64 0.96 0.15 asserted 1.00
s3 To this order, we also compute the Symanzik improvement coefficient necessary to remove the $\Oa$ lattice artefacts originating from the boundaries. contribution 0.69 0.95 0.09 asserted 1.00
s4 For reasonable lattice resolutions and the standard Wilson action, lattice artefacts are found to be only weakly dependent on the lattice spacing $a$, while they vanish quickly with the improved action of Sheikholeslami and Wohlert. result 0.99 0.93 0.20 asserted 1.00

What kind of paper the classifier reports this is: theoretical result 0.88 · evidence from proof or derivation 0.92.

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

References
How the literature uses it

44 arXiv papers cite this in 106 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 · 59 sentences without a confident label

Builds on it 2 papers
Uses its method or tool 19 papers
Uses its data or values 5 papers
Compares with it 6 papers
Cites it as background 6 papers

Discussion

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