Pion formfactor at intermediate momentum transfer in QCD

Ioffe, B.L.; Smilga, Andrei

doi:10.1016/0370-2693(82)90361-6

Cited by 180 publications

(214 citation statements)

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“…[6,7]. Their application to the pion form factor, based on axial vector interpolators, leads to a rather good agreement with experiment (in 3 the momentum transfer region 0.5 < Q 2 < 3.0 GeV 2 ) [6,7]. Our calculation will thus also provide a consistency check between the axial vector and pseudoscalar sum rules.…”

supporting

confidence: 70%

“…[6,7]. Their application to the pion form factor, based on axial vector interpolators, leads to a rather good agreement with experiment (in the momentum transfer region 0.5 < Q 2 < 3.0 GeV 2 ) [6,7].…”

supporting

confidence: 59%

“…Furthermore, correlators involving the pseudoscalar interpolators have a simpler tensor structure. This simplifies in particular the calculation of three-point functions.All existing sum rule applications in the pion channel (with the exception of ref.[5], see below), however, are based on axial vector current correlators [1,2,6,7]. The use of the pseudoscalar interpolating field has been avoided, since it is known to receive essential contributions from direct instantons [3].…”

mentioning

confidence: 99%

“…[6], the power corrections to Γ (pert) 1 are small in the Q 2 range under consideration 2 and will be neglected in this letter. A more complete analysis of the OPE can be found in [14].…”

mentioning

confidence: 99%

“…(6), is at present not 2 See also the related discussion for the two-point correlator in [3]. accurately known.…”

mentioning

confidence: 99%

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The electromagnetic pion form factor and instantons

Forkel

Nielsen

1995

Physics Letters B

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We calculate the electromagnetic pion form factor at intermediate spacelike momentum transfer from the QCD sum rule for the correlation function of two pseudoscalar interpolating fields and the electromagnetic current. This correlator receives essential contributions from direct (i.e. small-scale) instantons, which we evaluate under the assumption of an instanton size distribution consistent with instanton liquid and lattice simulations. The resulting form factor is in good agreement both with the sum rule based on the axial-current correlator and with experiment. * Address after Nov. 1, 1994: European Centre for Theoretical Studies in Nuclear Physics and Related Areas, Villa Tambosi, Strada delle Tabarelle 286, I-38050 Villazzano, Italy † Permanent address: Instituto de Física, Universidade de São Paulo, 01498 -SP-Brazil. 1A central goal of strong-interaction physics is the understanding of hadrons on the basis of quantum chromodynamics (QCD). It is very unlikely that this goal can be reached without a thorough understanding of the QCD vacuum. At present, however, direct links between observed hadron properties and the vacuum structure are still rare and rely mostly on extensive numerical simulations. The aim of this letter is to study one such link -between direct instantons, i.e. small-scale topological vacuum fields, and electromagnetic pion propertiesanalytically in the framework of a QCD sum rule [1,2].Due to the Goldstone nature of the pion, sum rule calculations of pionic properties can be based on two in principle (but not in practice!) equally suitable sets of correlation functions, corresponding to the use of pseudoscalar or axial vector interpolating fields. The pion couples strongly to both of these source currents and thus contributes to the correlators in both channels.The pseudoscalar channel has some principal advantages for sum rule calculations. The accuracy of the standard pole-continuum parametrization for the corresponding spectral functions profits from the almost complete dominance of the pion in the low-mass region [3,4]. Furthermore, correlators involving the pseudoscalar interpolators have a simpler tensor structure. This simplifies in particular the calculation of three-point functions.All existing sum rule applications in the pion channel (with the exception of ref.[5], see below), however, are based on axial vector current correlators [1,2,6,7]. The use of the pseudoscalar interpolating field has been avoided, since it is known to receive essential contributions from direct instantons [3]. Like instanton contributions in general, they could initially not be estimated reliably, due to insufficient knowledge of the instanton size distribution in the vacuum. The attempt of an ab initio description in the dilute gas approximation[8], in particular, failed for all but the smallest instanton sizes due to infrared problems with large instantons. The same problems were encountered in the attempt to supplement the conventional operator product expansion (OPE) in QCD sum rules with di...

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supporting

confidence: 70%

supporting

confidence: 59%

mentioning

confidence: 99%

“…[6], the power corrections to Γ (pert) 1 are small in the Q 2 range under consideration 2 and will be neglected in this letter. A more complete analysis of the OPE can be found in [14].…”

mentioning

confidence: 99%

“…(6), is at present not 2 See also the related discussion for the two-point correlator in [3]. accurately known.…”

mentioning

confidence: 99%

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