Perturbative QCD and electromagnetic form factors

We calculate nucleon magnetic form factors using perturbative QCD for several distribution amplitudes including a general one given in terms of Appell polynomials. We find that the magnitude and sign of both nucleon magnetic form factors can be explained within perturbative QCD. The observed normalization of $G_{\mathrm{Mp}}$ requires that the distribution amplitude be broader than its superhigh-momentum-transfer limit, and the $G_{\mathrm{Mn}}$/$G_{\mathrm{Mp}}$ data may require the distribution amplitude to be asymmetric, in accordance with distribution amplitudes derived from QCD sum rules. Some speculation as to how an asymmetric distribution amplitude can come about is offered. Finally, we show that the soft contributions corresponding to the particular distribution amplitudes we use need not be bigger than the data.