Timelike form factors at high energy

Abstract

The difference between the timelike and spacelike meson form factors is analyzed in the framework of perturbative QCD with Sudakov effects included. It is found that integrable singularities appear but that the asymptotic behavior is the same in the timelike and spacelike regions. The approach to asymptotia is quite slow and a rather constant enhancement of the timelike value is expected at a measurable large ${\mathit{Q}}^{2}$. This is in agreement with the trend shown by experimental data.