Soft contribution to form factors of the gamma *p--> Delta + transition.

Abstract

The purely nonperturbative soft contribution to the ${\ensuremath{\gamma}}^{*}p\ensuremath{\rightarrow}{\ensuremath{\Delta}}^{+}$ transition form factors is estimated using a model based on the local quark-hadron duality. In this approach, the soft contribution is shown to be dominated by the magnetic transition: the ratio $\frac{{G}_{E}^{*}({Q}^{2})}{{G}_{M}^{*}({Q}^{2})}$ is small for all accessible ${Q}^{2}$, in contrast with PQCD expectation that ${G}_{E}^{*}({Q}^{2})\ensuremath{\rightarrow}\ensuremath{-}{G}_{M}^{*}({Q}^{2})$. We also found that the soft contribution to the magnetic form factor is large enough to explain the magnitude of existing experimental data.