Isovector Electromagnetic Form Factors

Abstract

Isovector electromagnetic form factors are calculated by dispersion-theoretic methods, keeping only the two-pion intermediate states. The pion form factor, which plays a particularly important role, is obtained from effective-range theory and a comparison with data from recent colliding-beam experiments. Annihilation amplitudes ($N\overline{N}\ensuremath{\rightarrow}\ensuremath{\pi}\ensuremath{\pi}$, $K\overline{K}\ensuremath{\rightarrow}\ensuremath{\pi}\ensuremath{\pi}$, etc.) are calculated by a method of pole dominance discussed in a previous paper and a technique for incorporating universality of $\ensuremath{\rho}$-meson couplings. Agreement with experiment is achieved for the two isovector radii of the nucleon, even though the calculated form factors do not fall fast enough at high momentum transfer.