Two-loop form factors in QED Original Research Article

We evaluate the on shell form factors of the electron for arbitrary momentum transfer and finite electron mass, at two loops in QED, by integrating the corresponding dispersion relations, which involve the imaginary parts known since a long time. The infrared divergences are parameterized in terms of a fictitious small photon mass. The result is expressed in terms of harmonic polylogarithms of maximum weight 4. The expansions for small and large momentum transfer are also given.