Dispersion analysis of the strange vector form factors of the nucleon

Abstract

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 ${(r}_{s}^{2}{)}_{\mathrm{Sachs}}=0.20 {\mathrm{fm}}^{2}$ and a by 20% reduced magnitude of the strangeness magnetic moment ${\ensuremath{\mu}}_{s}=\ensuremath{-}0.26$. 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 $\ensuremath{\varphi}$-meson couplings and are generic in the pole approximation.