Electromagnetic Form Factors at Large Momentum Transfer

Abstract

Recent improvements of the hard scattering picture for the large $p_{\perp}$ behaviour of electromagnetic form factors, namely the inclusion of both Sudakov corrections and intrinsic transverse momentum dependence of the hadronic wave function, are reviewed. On account of these improvements the perturbative contributions to the pion's and the nucleon's form factor can be calculated in a theoretically self-consistent way for momentum transfers as low as about $2$ and $3\,{\rm GeV}$, respectively. This is achieved at the expense of a substantial suppression of the perturbative contribution in the few GeV region. Eventual higher twist contributions are discussed in some detail.