Empirical parametrizations of the resonance amplitudes based on the Siegert's theorem

Abstract

We present parametrizations of the ${\gamma }^{\ast }N\to N(1535)1/2^{-}$, ${\gamma }^{\ast }N\to N(1520)3/2^{-}$ and ${\gamma }^{\ast }N\to \Delta (1232)3/2^{+}$ transition amplitudes that are compatible with the analytic constraints at the pseudothreshold (Siegert's theorem). The presented parametrizations also provide a fair description of the experimental data. For the case of the ${\gamma }^{\ast }N\to \Delta (1232)3/2^{+}$ transition, we discuss how the pion cloud parametrizations of the electric and the Coulomb quadrupole form factors can be adjusted according to the Siegert's theorem.

Comments: Proceedings of the "The 14th International Conference on Meson-Nucleon Physics and the Structure of the Nucleon". July 25-30, 2016, Kyoto, Japan. 5 pages, 4 figures