Abstract
We analyze the basic hard exclusive processes, the -transition and the pion and nucleon electromagnetic form factors, and discuss the analytic continuation of QCD formulas from the spacelike to the timelike region of the relevant momentum transfers. We describe the construction of the timelike version of the coupling constant We show that due to the analytic continuation of the collinear logarithms, each eigenfunction of the evolution equation acquires a phase factor and investigate the resulting interference effects which are shown to be very small. We find no sources for the K-factor-type enhancements in the perturbative QCD contribution to the hadronic form factors. To study the soft part of the pion electromagnetic form factor, we use a QCD sum rule inspired model and show that there are noncanceling Sudakov double logarithms which result in a K-factor-type enhancement in the timelike region.
- Received 19 June 2000
DOI:https://doi.org/10.1103/PhysRevD.62.113001
©2000 American Physical Society