Form Factors and QCD in Spacelike and Timelike Region

Abstract

We analyze the basic hard exclusive processes: πγ*γ- transition, pion and nucleon electromagnetic form factors, and discuss the analytic continuation of QCD formulas from the spacelike q^2<0 to the timelike region q^2 >0 of the relevant momentum transfers. We describe the construction of the timelike version of the coupling constant α_s. We show that due to the analytic continuation of the collinear logarithms each eigenfunction of the evolution equation acqiures a phase factor and investigate the resulting interference effects which are shown to be very small. We found 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 non-canceling Sudakov double logarithms which result in a K-factor-type enhancement in the timelike region.

12 pages, LaTeX; a few typos corrected, references added

References in corpus (2)

• Pion Form Factor in QCD at Intermediate Momentum Transfers
• Improvement of perturbation theory in QCD for e^+e^- -> hadrons and the problem of α_s freezing

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