0000000000246349
AUTHOR
R. Tegen
The energy dependence of Zweig-rule-violating couplings. A dynamical calculation of ϕ → ρπ
It has been argued that the violation of the Zweig rule is strongly dependent on the kinematical region, especially that it should decrease for large timeliket (asymptotic planarity). We have calculated thet-dependence of the vertex ϕρπ with two different methods, the first one using partial-wave dispersion relations and unitarity and the second one based on FESR and duality. The decrease in the timelike region is confirmed by both calculations. In the spacelike region the energy dependence of the Zweig-rule-violating coupling depends on the method of continuation to off-shell values. We only find an energy dependence if the full amplitude πρ → K $$\bar K$$ is taken into account.
Isovector and isoscalar meson cloud contributions to the nucleon electromagnetic form factors
We have calculated the nucleon form factors ${G}_{E,M}^{(p,n)}{(q}^{2})$ in the linear \ensuremath{\sigma} model to one-meson-loop order plus (two-loop) $\ensuremath{\gamma}\ensuremath{\pi}\ensuremath{\pi}\ensuremath{\pi}$ anomaly. The previously derived $\ensuremath{\gamma}\ensuremath{\pi}\ensuremath{\pi}\ensuremath{\pi}$ anomaly generally reduces the nucleon radii and produces a shift of the magnetic moments of order 0.1 ${\ensuremath{\mu}}_{N}$ or less. We present analytical results for ${G}_{E,M}^{p,n}(0)$ 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 $(\mathrm{…