Meson cloud corrections to the pion electromagnetic form-factor in the Nambu-Jona-Lasinio model
199526 pages
Published in:
- Nucl.Phys.A 593 (1995) 315-340
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Abstract: (Elsevier)
We have calculated lowest order meson cloud corrections to the pion electromagnetic form factor in the two-flavor NJL model. The complete set of gauge and chirally invariant Feynman diagrams falls naturally into two distinct classes: hadronic tadpole and pion-pole diagrams, respectively. Only their sum respects gauge invariance, Goldstone's theorem, the Goldberger-Treiman relation and conserves the axial current. We demonstrate that hadronic tadpole diagrams can be neglected in the static approximation of infinite quark masses, while only a single pion-pole diagram survives that is, however, too weak to reproduce the strong, ϱ-like vector correlations that are inferred experimentally above the ππ-threshold. The meson cloud contributes less than 10% to the size of the basic NJL electromagnetic form factor of the pion, but drastically alters its gradient at zero momentum transfer. This general feature is in the model due to a singularity introduced by the pion-pole diagram in the chiral limit and contributes the well-known logarithmic term to the pion electromagnetic radius, here at scale μ = m σ given by the sigma mode mass.- pi: form factor
- form factor: pi
- Jona-Lasinio-Nambu model
- Feynman graph
- invariance: gauge
- invariance: chiral
- scalar meson: exchange
- exchange: scalar meson
- postulated particle: f0(600)
- numerical calculations
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