Dominant NNLO corrections to four-fermion production near the W-pair production threshold

We calculate the parametrically dominant next-to-next-to-leading order corrections to four-fermion production e−e+→μ−ν¯μud¯+X at centre-of-mass energies near the W-pair production threshold employing the method of unstable-particle effective theory. In total the correction is small, leading to a shift of 3 MeV in the W-mass measurement. We also discuss the implementation of realistic cuts and provide a result for the interference of single-Coulomb and soft radiative corrections that can easily be extended to include an arbitrary number of Coulomb photons.