A Simple Approximation of the One-Loop Corrected Cross Section for $e^+e^-\to W^+W^-$ at LEP 2

Using the SU(2) gauge coupling, $g_{W^\pm} (M^2_{W^\pm})$, at the high-energy scale of $M_{W^\pm}$, defined by the (theoretical value of the) leptonic W-width, rather than using the low-energy value, defined via the Fermi coupling, $G_\mu$, in the Born approximation, and supplementing with Coulomb corrections and initial state radiation, errors with respect to the exact one-loop results for the differential cross section of $e^+e^-\to W^+W^-$ are below 1% at LEP 2 energies at all $W^+W^-$ production angles. A similar procedure is suggested to incorporate leading bosonic loop effects into four-fermion production in the fermion-loop scheme. The resulting accuracy below 1% is sufficient for LEP 2 experiments.