Isovector and isoscalar meson cloud contributions to the nucleon electromagnetic form factors
- Institut fuer Kernphysik, Johannes Gutenberg--Universitaet Mainz, D-55099 Mainz (Germany)
We have calculated the nucleon form factors G{sub E,M}{sup (p,n)}(q{sup 2}) in the linear {sigma} model to one-meson-loop order plus (two-loop) {gamma}{pi}{pi}{pi} anomaly. The previously derived {gamma}{pi}{pi}{pi} anomaly generally reduces the nucleon radii and produces a shift of the magnetic moments of order 0.1 {mu}{sub N} or less. We present analytical results for G{sub E,M}{sup p,n}(0) which display explicitly their dependence on hadron masses and coupling constants. Analytical results for the radii are also given and the chiral singularities they contain (lnm{sub {pi}} and m{sub {pi}}{sup {minus}1}) are exposed. These come from the {pi}{pi} intermediate state contribution to the form factors and {ital not} from the chiral quark substructure of nucleons or mesons. The leading chiral singularity has a {ital universal} strength while the chiral log (next-to-leading singularity) picks up a model (or approximation) dependence in terms of g{sub A} and the threshold behavior of the {pi}N amplitude A{sup ({minus})}({nu},0). The chiral singularities appear only in the iso{ital vector} nucleon radii {l_angle}r{sub 1,2}{sup 2}{r_angle}{sup I=1}, the leading m{sub {pi}}{sup {minus}1} term appears only in {l_angle}r{sub 2}{sup 2}{r_angle}{sup I=1} due to a peculiar cancellation between two independent form factor combinations {Gamma}{sub 1,3}(q{sup 2}). The isoscalar anomaly {gamma}{pi}{pi}{pi} is finite for m{sub {pi}}{r_arrow}0. {copyright} {ital 1998} {ital The American Physical Society}
- OSTI ID:
- 566019
- Journal Information:
- Physical Review, C, Journal Name: Physical Review, C Journal Issue: 1 Vol. 57; ISSN 0556-2813; ISSN PRVCAN
- Country of Publication:
- United States
- Language:
- English
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