The pion form factor from analyticity and unitarity

Abstract

Analyticity and unitarity techniques are employed to estimate Taylor coefficients of the pion electromagnetic form factor at t = 0 by exploiting the recently evaluated two-pion contribution to the muon (g − 2) and the phase of the pion electromagnetic form factor in the elastic region, known from ππ scattering by Fermi–Watson theorem and the values of the form factor at several points in the space-like region. Regions in the complex t-plane are isolated where the form factor cannot have zeros.