DPG Phi
Verhandlungen
Verhandlungen
DPG

Bochum 1998 – wissenschaftliches Programm

Bereiche | Tage | Auswahl | Suche | Downloads | Hilfe

HK: Hadronen und Kerne

HK 36: Electromagnetic Probes V, CERN, HERA Results

HK 36.1: Gruppenbericht

Dienstag, 17. März 1998, 17:00–17:30, B

Spectral functions of Nucleon Form Factors near Threshold — •Norbert Kaiser2, Véronique Bernard1, and Ulf-G. Meißner31Univ. Louis Pasteur, Strasbourg, France — 2Technische Universität München, Physik Department T39 — 3FZ Jülich, IKP (Th)

We investigate the spectral functions of the electromagnetic and axial nucleon form factors near threshold in chiral perturbation theory. From dispersion theory it is known that the spectral functions of the isovector electromagnetic form factors are strongly enhanced near threshold t=4mπ2. This effect originates from a logarithmic singularity at the anomalous threshold tc=4mπ2mπ4/M2=3.98 mπ2 on the second Riemann sheet. We are able to reproduce in one-loop approximation the near threshold part of the isovector electromagnetic spectral functions (after subtracting the ρ(770)-contribution). Then we clarify the up to now open question whether a similar strong enhancement occurs in the isoscalar electromagnetic form factors near t=9mπ2. We calculate the imaginary parts of the corresponding two loop diagrams and find no visible enhancement. The three-body phase space masks the singularity at a nearby anomalous threshold at t=8.9 mπ2. Similarly small is the contribution of the three-pion continuum to the isovector axial form factor.

[1] V. Bernard, N. Kaiser and Ulf-G. Meißner, Nucl. Phys. A611 (1996) 429.

100% | Mobil-Ansicht | English Version | Kontakt/Impressum/Datenschutz
DPG-Physik > DPG-Verhandlungen > 1998 > Bochum