Hadronic corrections to the muon decay
  We consider the O(alpha^2) hadronic corrections to the energy spectrum of the decay electron in muon decay. We find that the correction can be described, within good approximation, by a linear function in the electron energy. Explicit expressions for the form factors needed in an approach based on dispersion integrals are given. 
A.I. Davydychev, K. Schilcher, H. Spiesberger