The pion form factor from analyticity and unitarity

摘要

Analyticity and unitarity techniques are employed to estimate Taylor coefficients of the pion electromagnetic form factor at e?‘? = 0 by exploiting the recently evaluated two-pion contribution to the muon (e?‘” a?’ 2) and the phase of the pion electromagnetic form factor in the elastic region, known from e??? e??? scattering by Fermia€“Watson theorem and the values of the form factor at several points in the space-like region. Regions in the complex e?‘?-plane are isolated where the form factor cannot have zeros.