TTP08-15 Heavy-Flavor Contribution to Bhabha Scattering

We evaluate the last missing piece of the two-loop QED corrections to the high-energy electron-positron scattering cross section originated from the vacuum polarization by heavy fermions. The calculation is performed within a new approach applicable to a wide class of perturbative problems with mass hierarchy. The result is crucial for the high-precision physics program at existing and future $e^+e^-$ colliders.