Extrapolation of Nucleon Form Factors. II

The magnetic isoscalar form factor is fitted with two poles: the $\omega$ and the $\phi$ resonance. The magnetic isovector form factor $G_{\mathrm{MV}}$ for spacelike and timelike momentum transfers is fitted using the conformal-transformation techniques of Levinger, Peierls, and Wang, and these techniques are tested using artificial data. If we do not assume a contribution from the $\rho$ resonance, we find a spectral function with a broad peak some 100 MeV below the position of the $\rho$, and with a negative dip around 1200 MeV. If we assume that the $\rho$ resonance contributes additively at its known position and width, but with an adjustable coefficient for its strength, we argue that the $\rho$ contributes about 90% of the static moment. The complete spectral function shows a shoulder around 500 MeV, and again a negative dip around 1200 MeV. If we assume that $G_{\mathrm{MV}}$ is a product of the form factor for the $\rho$ and an adjustable function, we find that the spectral function has a high peak near the $\rho$ resonance, and a marked negative dip at 900 MeV. The $\rho$ again contributes some 90% of the static moment. The different phenomenonological fits are in semiquantitative agreement with each other and with the recent field-theoretical calculations of Furuichi et al.