Dispersion analysis of the strange vector form factors of the nucleon

We analyze the nucleon matrix element of the strange quark vector current in a nucleon-model-independent dispersive approach with input from the current world data set for the isoscalar electromagnetic form factors. The update of Jaffe’s minimal three-pole Ansatz for the spectral functions yields a 40% larger (Sachs) strangeness radius ${(r}_s^2{)}_{\mathrm{Sachs}}=0.20\mathrm{}\hspace{0.5em}{\mathrm{fm}}^2$ and a by 20% reduced magnitude of the strangeness magnetic moment ${\mu }_s=-0.26$. In the pole approximation these values are shown to be upper bounds. After extending the Ansatz in order to implement the asymptotic QCD momentum dependence (which the three-pole form factors cannot reproduce), we find the magnitude of the three-pole results reduced by up to a factor of 2.5. The signs of the leading moments originate primarily from the large $\phi$-meson couplings and are generic in the pole approximation.