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Ioffe-time distributions instead of parton momentum distributions in description of deep inelastic scattering

High Energy Physics - Phenomenology · Submitted 19 Oct 1994 · 23 references

Pith's verdict: The framework is borrowed, but the sum rule evaluation is new and the u-quark agreement is a real check — the z ≤ 4 claim just runs past the authors' own convergence bound.

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arXiv IDhep-ph/9410318 (version 2)
Pith IDBIGRCWFV, Pith's permanent record of this paper and its review
CitationL. Mankiewicz, P. G\'ornicki, V. Braun. "Ioffe-time distributions instead of parton momentum distributions in description of deep inelastic scattering." arXiv:hep-ph/9410318 (1994). https://pith.science/paper/BIGRCWFV
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Referee report
The paper

The paper claims

Parton distributions are better computed in coordinate space than in momentum space, and a QCD sum rule shows it for the proton's up quark.

The reading

The paper argues that the usual momentum-fraction parton distributions are the wrong object to hand to a nonperturbative method: a fixed value of Bjorken $x$ mixes physics from short and long longitudinal distances, and that mixing shows up as singular, delta-function-like terms in the operator product expansion. The authors propose instead the Ioffe-time distribution, the Fourier transform of the momentum distribution with respect to the light-cone distance travelled by the struck quark, which is a smooth function given directly by a proton matrix element of a nonlocal quark string operator on the light cone. They derive the evolution equations for these distributions directly in coordinate space, where the scale derivative at separation $z$ involves the distribution only at smaller separations, and then compute the valence distributions with QCD sum rules. The calculation reproduces the fitted up-quark distribution out to Ioffe time $z$ of about 4 and fails for the down quark, which the authors trace to the particular structure of the expansion in that channel rather than to the coordinate-space formulation itself.

What carries the argument

The load-bearing object is the Ioffe-time distribution itself, $Q_{ig!rm val}(z,ig!mu^2) = ig!int_0^1 du, ig!cos(uz), q_V(u,ig!mu^2)$, identified with a proton matrix element of a nonlocal light-cone operator carrying a path-ordered exponential. Two pieces of machinery make it usable. First, the coordinate-space evolution equation $ig!mu^2 ig!partial_{ig!mu^2} Q_{ig!rm val}(z;ig!mu^2) = -ig!frac{ig!alpha_s}{2ig!pi}C_F ig!int_0^1 du, K(u), Q_{ig!rm val}(uz;ig!mu^2)$, which shows that the scale dependence at separation $z$ is fixed entirely by the distribution at smaller separations, so the short-distance expansion is visible in the equation itself, unlike the case for fragmentation functions. Second, the sum rule: a double Borel transform in $p_1^2$ and $p_2^2$ with continuum subtraction, plus a Ward identity relating the three-point correlator at $ig!Delta = 0$ to the derivative of the two-point correlator, which enforces the normalization $ig!int du, q_V(u) = N_u = 2$ and $N_d = 1$. The same Ward identity converts the most important bilocal power corrections into contact terms, that is, into ordinary local condensate contributions.

Extended reading notes

Core claim

The central claim is that coordinate-space (Ioffe-time) parton distributions are the natural target for nonperturbative QCD, and that a standard QCD sum rule can actually deliver them for the proton's valence quarks. Using a three-point correlator of two nucleon interpolating currents with the nonlocal vector operator $P e^{ig!int A}$-dressed $ig!bar{Psi}(ig!Delta)ig!slashed{n}[ig!Delta;0]ig!Psi(0)$, the authors obtain sum rules whose coefficient functions are smooth functions of $z$, in contrast to the momentum-space version where the same terms become $ig!delta(u)$, $ig!delta(1-u)$ and derivatives thereof. Keeping perturbative, dimension-4, dimension-6 and dimension-8 contributions, the up-quark Ioffe-time distribution agrees with the Glück–Reya–Vogt fit up to $z ig!simeq 4$, quoted as light-cone distances of order 1 to 2 fm in the proton rest frame; the abstract says about 1 fm while the text says nearly 2 fm, reflecting a factor-of-two convention between light-cone and physical longitudinal distance that the paper states explicitly. The down-quark distribution comes out much shorter-ranged than the fit. The authors attribute this to a $ig!cos z$ term from the diagram in which one quark carries the whole proton momentum, to the absence of the dimension-6 bilocal correction in that channel, and to strong cancellation between dimension-6 and dimension-8 condensate contributions that makes the result sensitive to the normalization point.

Load-bearing premise

That truncating the operator product expansion at dimension 8, and dropping the bilocal power corrections that contain explicit gluon fields (a neglect the authors state in the Appendix), leaves the up-quark prediction numerically intact at $z$ near 4.

Editorial extensions

If this is right

  • If coordinate-space distributions are the right interface, lattice QCD and instanton-vacuum models can supply parton distributions at moderate $z$ without the singular-term problem that afflicts momentum-space sum rules.
  • The coordinate-space evolution equations give a practical alternative to the usual momentum-space GLAP equations, with the large-$z$ tail being the part that moves most between 4 and 20 GeV$^2$.
  • Matching the calculated small-$z$ region onto the Regge asymptotic form $ig!sim z^{ig!alpha+1}$ at $z ig!sim 5$ to 8 would reconstruct the full Ioffe-time distribution and hence, by Fourier transform, the momentum-space distribution.
  • The same construction applies to the polarized gluon distribution, where knowledge of $ig!Delta G(z)$ up to its maximum at $z ig!sim 6$ would fix the total gluon polarization to roughly 50 percent accuracy.
  • For the down quark, the failure points at the need for a different interpolating current, radiative corrections, or a large bilocal correction behaving as $z^2$ in coordinate space.

Reading between the lines

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

  • The argument is really about conditioning: a Fourier transform turns a delta-function-dominated expansion into a smooth one, so the same operator product expansion is far better behaved in $z$ than in $u$. This could be quantified by comparing the convergence of the two expansions term by term, which the paper does not do.
  • If the finite correlation length of the vacuum is what pushes nonperturbative strength away from $u ig!to 1$, then momentum-space sum rule calculations truncated at local operators will systematically over-weight the endpoint region, a bias that could be checked against existing fits.
  • The paper's own 'matching window' question, whether a region exists where both the small-$z$ expansion and the Regge asymptotics apply, is empirically answerable with present fits; the figures suggest $z ig!sim 5$ to 8, which is already where the sum rule is failing, so the window may be narrow or absent in the down-quark channel.
  • A useful independent test would be to compute the same Ioffe-time distributions with a different nonperturbative method and see whether the up/down asymmetry of agreement persists; if it does, it is a property of the interpolating current rather than of the coordinate-space formulation.
Original abstract

We argue that parton distributions in coordinate space provide a more natural object for nonperturbative methods compared to the usual momentum distributions in which the physics of different longitudinal distances is being mixed. To illustrate the advantages of the coordinate space formulation, we calculate the coordinate space distributions for valence quarks in the proton using the QCD sum rule approach. A remarkable agreement is found between the calculated and the experimentally measured u-quark distribution up to light-cone distances $\Delta^- = \Delta^0 - \Delta^3$ of order $\sim 1$ fm in the proton rest frame. The calculation for valence d quarks gives much worse results; the reasons for this discrepancy are discussed.

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, 3,667 input tokens, $0.0002 reported.

What the abstract itself states, as probabilities: claims first 0.04 · states limitation 0.95 · human participants 0.02 · controlled comparison 0.12 · randomized assignment 0.01 · states quantitative result 0.85 · compares with prior results 0.80 · mentions code or data availability 0.02.

The abstract, sentence by sentence

arXiv listing abstract v2. Results and the main claim are underlined; .

We argue that parton distributions in coordinate space provide a more natural object for nonperturbative methods compared to the usual momentum distributions in which the physics of different longitudinal distances is being mixed. To illustrate the advantages of the coordinate space formulation, we calculate the coordinate space distributions for valence quarks in the proton using the QCD sum rule approach. A remarkable agreement is found between the calculated and the experimentally measured u-quark distribution up to light-cone distances $\Delta^- = \Delta^0 - \Delta^3$ of order $\sim 1$ fm in the proton rest frame. The calculation for valence d quarks gives much worse results; the reasons for this discrepancy are discussed.

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 We argue that parton distributions in coordinate space provide a more natural object for nonperturbative methods compared to the usual momentum distributions in which the physics of different longitudinal distances is being mixed. contribution 0.47 0.26 0.67 asserted 0.60
s1 To illustrate the advantages of the coordinate space formulation, we calculate the coordinate space distributions for valence quarks in the proton using the QCD sum rule approach. method 0.51 0.95 0.07 asserted 0.97
s2 A remarkable agreement is found between the calculated and the experimentally measured u-quark distribution up to light-cone distances $\Delta^- = \Delta^0 - \Delta^3$ of order $\sim 1$ fm in the proton rest frame. result 1.00 0.91 0.37 asserted 1.00
s3 The calculation for valence d quarks gives much worse results; the reasons for this discrepancy are discussed. limitation 0.73 0.90 0.05 asserted 0.99

What kind of paper the classifier reports this is: theoretical result 0.71 · evidence from simulation or computation 0.93.

What was examined, and what was not

sources read
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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 1. Ioffe time distributions for partons at the scale µ 2 = 4 GeV2 . The solid line denotes Gl¨uck, Reya, Vogt (GRV) [3] set of parametrizations, the dashed line denotes CTEQ [4] parametrization. Uval(z) and Dval(z) are the valence quarks distributions, QU (z) and QD(z) are the C-even up and down quark distributions, and G(z) is the gluon distribution
Figure 2. Model of the Ioffe time valence-type distribution corresp
Figure 3. Model of the Ioffe time distributions for polarized gluon den
Figure 4. Evolution of valence Uval(z, Q2 ) and Dval(z, Q2 ), and gluon G(z, Q2 ) Ioffe time distributions. GRV [3] parametrisation has been used. The solid line corresponds to Q2 = 4 GeV2 , the dashed line to Q2 = 20 GeV2 , respectively. 29
Figure 5. Evolution of up and down quark C-even QU (z, Q2 ) and QD(z, Q2 ) Ioffe time distributions. GRV [3] parametrisation has been used. The solid line corresponds to Q2 = 4 GeV2 , the dashed line to Q2 = 20 GeV2 , respectively. 30
Figure 6. Typical diagrams contributing to the OPE of the correlato
Figure 7. Generic form of a bilocal correction in the OPE of the corre
Figure 8. QCD sum rules calculation of the valence u-quark Ioffe time d
Figure 9. Stability of the sum rule for Uval(z) against variation of the Borel parameter t. The upper curve corresponds to t = 1 GeV2 , the lower to t = 1.5 GeV2 . 34
Figure 10. The sum rule prediction for Dval(z), shown as the thick solid line, is rather far from the leading-order GRV [18] parametrisation, and is much more short-range. As 15
Figure 11. The nonlocal condensate contribution to the d-quark sum rule, see Eq.(65). Lines marked as (a) and (b) correspond to the diquark mass parameters MD = 0.7 GeV and 1.0 GeV, respectively. Borel parameter t = 1 GeV2
Figure 12. QCD sum rules calculation of the valence d-quark Ioffe time
Figure 13. Graphical illustration of the Ward identity, Eq.(A.5). Dashed lines denote path￾ordered exponentials. 23

Figures reproduced from arXiv:hep-ph/9410318 by the authors.

References
How the literature uses it

47 arXiv papers cite this in 73 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 · 33 sentences without a confident label

Uses its method or tool 1 paper
Cites it as background 33 papers

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